From: alexlamsl Date: Mon, 1 Feb 2016 17:43:59 +0000 (+0800) Subject: removed es6-draft X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=054741ca0a9ea8b3c85752da496f88029dc1156d;p=html-minifier.git removed es6-draft --- diff --git a/benchmark.js b/benchmark.js index 0456806..7b07d01 100644 --- a/benchmark.js +++ b/benchmark.js @@ -19,15 +19,14 @@ var fileNames = [ 'abc', 'amazon', 'eloquentjavascript', - 'es6-draft', + 'es6', 'es6-table', 'google', 'html-minifier', 'msn', 'newyorktimes', 'stackoverflow', - 'wikipedia', - 'es6' + 'wikipedia' ].sort(); var table = new Table({ diff --git a/benchmarks/es6-draft.html b/benchmarks/es6-draft.html deleted file mode 100644 index deff8ac..0000000 --- a/benchmarks/es6-draft.html +++ /dev/null @@ -1,57030 +0,0 @@ - - - - - ECMAScript Language Specification ECMA-262 6th Edition – DRAFT - - - - -
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This is not the official ECMAScript Language Specification.

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This is a draft of the next edition of the standard. See also:

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For copyright information, see Ecma International’s legal disclaimer in the document itself.

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ECMA-262

-

6th Edition / Draft May 22, 2014

-

Draft

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-

ECMAScript Language Specification

- -

Draft

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Report Errors and Issues at: https://bugs.ecmascript.org

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Product: Draft for 6th Edition

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Component: choose an appropriate one

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Version: Rev 25, May 22, 2014 Draft

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Ecma/TC39/2014/0xx

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Contents

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    -
  1. Introduction
    2. -
  2. 1 Scope
    3. -
  3. 2 Conformance
    4. -
  4. 3 Normative references
    5. -
  5. 4 Overview -
      -
    1. 4.1 Web Scripting
      2. -
    2. 4.2 ECMAScript Overview -
        -
      1. 4.2.1 Objects
        2. -
      2. 4.2.2 The Strict Variant of - ECMAScript
        3. -
      -
      3. -
    3. 4.3 Terms and definitions -
        -
      1. 4.3.1 type
        2. -
      2. 4.3.2 primitive value
        3. -
      3. 4.3.3 object
        4. -
      4. 4.3.4 constructor
        5. -
      5. 4.3.5 prototype
        6. -
      6. 4.3.6 ordinary object
        7. -
      7. 4.3.7 exotic object
        8. -
      8. 4.3.8 standard object
        9. -
      9. 4.3.9 built-in object
        10. -
      10. 4.3.10 undefined value
        11. -
      11. 4.3.11 Undefined type
        12. -
      12. 4.3.12 null value
        13. -
      13. 4.3.13 Null type
        14. -
      14. 4.3.14 Boolean value
        15. -
      15. 4.3.15 Boolean type
        16. -
      16. 4.3.16 Boolean object
        17. -
      17. 4.3.17 String value
        18. -
      18. 4.3.18 String type
        19. -
      19. 4.3.19 String object
        20. -
      20. 4.3.20 Number value
        21. -
      21. 4.3.21 Number type
        22. -
      22. 4.3.22 Number object
        23. -
      23. 4.3.23 Infinity
        24. -
      24. 4.3.24 NaN
        25. -
      25. 4.3.25 Symbol value
        26. -
      26. 4.3.26 Symbol type
        27. -
      27. 4.3.27 Symbol object
        28. -
      28. 4.3.28 function
        29. -
      29. 4.3.29 built-in function
        30. -
      30. 4.3.30 property
        31. -
      31. 4.3.31 method
        32. -
      32. 4.3.32 built-in method
        33. -
      33. 4.3.33 attribute
        34. -
      34. 4.3.34 own property
        35. -
      35. 4.3.35 inherited property
        36. -
      -
      4. -
    4. 4.4 Organization of This - Specification
      5. -
    -
    6. -
  6. 5 Notational Conventions -
      -
    1. 5.1 Syntactic and Lexical Grammars -
        -
      1. 5.1.1 Context-Free Grammars
        2. -
      2. 5.1.2 The Lexical and RegExp - Grammars
        3. -
      3. 5.1.3 The Numeric String Grammar
        4. -
      4. 5.1.4 The Syntactic Grammar
        5. -
      5. 5.1.5 Grammar Notation
        6. -
      -
      2. -
    2. 5.2 Algorithm Conventions
      3. -
    3. 5.3 Static Semantic Rules
      4. -
    -
    7. -
  7. 6 ECMAScript Data Types and Values -
      -
    1. 6.1 ECMAScript Language Types -
        -
      1. 6.1.1 The Undefined - Type
        2. -
      2. 6.1.2 The Null Type
        3. -
      3. 6.1.3 The Boolean Type
        4. -
      4. 6.1.4 The String Type
        5. -
      5. 6.1.5 The Symbol Type
        6. -
      6. 6.1.6 The Number Type
        7. -
      7. 6.1.7 The Object Type
        8. -
      -
      2. -
    2. 6.2 ECMAScript Specification Types -
        -
      1. 6.2.1 The List and Record - Specification Type
        2. -
      2. 6.2.2 The Completion Record - Specification Type
        3. -
      3. 6.2.3 The Reference Specification - Type
        4. -
      4. 6.2.4 The Property - Descriptor Specification Type
        5. -
      5. 6.2.5 The Lexical - Environment and Environment Record Specification Types
        6. -
      6. 6.2.6 Data Blocks
        7. -
      -
      3. -
    -
    8. -
  8. 7 Abstract Operations -
      -
    1. 7.1 Type Conversion and Testing -
        -
      1. 7.1.1 ToPrimitive
        2. -
      2. 7.1.2 ToBoolean
        3. -
      3. 7.1.3 ToNumber
        4. -
      4. 7.1.4 ToInteger
        5. -
      5. 7.1.5 ToInt32: (Signed 32 Bit Integer)
        6. -
      6. 7.1.6 ToUint32: (Unsigned 32 Bit Integer)
        7. -
      7. 7.1.7 ToInt16: (Signed 16 Bit Integer)
        8. -
      8. 7.1.8 ToUint16: (Unsigned 16 Bit Integer)
        9. -
      9. 7.1.9 ToInt8: (Signed 8 Bit Integer)
        10. -
      10. 7.1.10 ToUint8: (Unsigned 8 Bit Integer)
        11. -
      11. 7.1.11 ToUint8Clamp: (Unsigned 8 Bit Integer, - Clamped)
        12. -
      12. 7.1.12 ToString
        13. -
      13. 7.1.13 ToObject
        14. -
      14. 7.1.14 ToPropertyKey
        15. -
      15. 7.1.15 ToLength
        16. -
      16. 7.1.16 - CanonicalNumericIndexString(argument)
        17. -
      -
      2. -
    2. 7.2 Testing and Comparison Operations -
        -
      1. 7.2.1 CheckObjectCoercible ( argument )
        2. -
      2. 7.2.2 IsCallable ( argument )
        3. -
      3. 7.2.3 SameValue(x, y)
        4. -
      4. 7.2.4 SameValueZero(x, y)
        5. -
      5. 7.2.5 IsConstructor ( argument )
        6. -
      6. 7.2.6 IsPropertyKey ( argument )
        7. -
      7. 7.2.7 IsExtensible (O)
        8. -
      8. 7.2.8 IsInteger ( argument )
        9. -
      9. 7.2.9 Abstract Relational - Comparison
        10. -
      10. 7.2.10 Abstract Equality - Comparison
        11. -
      11. 7.2.11 Strict Equality Comparison
        12. -
      -
      3. -
    3. 7.3 Operations on Objects -
        -
      1. 7.3.1 Get (O, P)
        2. -
      2. 7.3.2 Put (O, P, V, Throw)
        3. -
      3. 7.3.3 CreateDataProperty (O, P, V)
        4. -
      4. 7.3.4 CreateDataPropertyOrThrow (O, P, - V)
        5. -
      5. 7.3.5 DefinePropertyOrThrow (O, P, desc)
        6. -
      6. 7.3.6 DeletePropertyOrThrow (O, P)
        7. -
      7. 7.3.7 GetMethod (O, P)
        8. -
      8. 7.3.8 HasProperty (O, P)
        9. -
      9. 7.3.9 HasOwnProperty (O, P)
        10. -
      10. 7.3.10 Invoke(O,P, [args])
        11. -
      11. 7.3.11 SetIntegrityLevel (O, level)
        12. -
      12. 7.3.12 TestIntegrityLevel (O, level)
        13. -
      13. 7.3.13 CreateArrayFromList (elements)
        14. -
      14. 7.3.14 CreateListFromArrayLike (obj)
        15. -
      15. 7.3.15 OrdinaryHasInstance (C, O)
        16. -
      16. 7.3.16 GetPrototypeFromConstructor ( - constructor, intrinsicDefaultProto )
        17. -
      17. 7.3.17 CreateFromConstructor (F)
        18. -
      18. 7.3.18 Construct (F, argumentsList)
        19. -
      19. 7.3.19 GetOption (options, P)
        20. -
      -
      4. -
    4. 7.4 Operations on Iterator Objects -
        -
      1. 7.4.1 CheckIterable ( obj )
        2. -
      2. 7.4.2 GetIterator ( obj, method )
        3. -
      3. 7.4.3 IteratorNext ( iterator, value )
        4. -
      4. 7.4.4 IteratorComplete ( iterResult )
        5. -
      5. 7.4.5 IteratorValue ( iterResult )
        6. -
      6. 7.4.6 IteratorStep ( iterator )
        7. -
      7. 7.4.7 CreateIterResultObject (value, - done)
        8. -
      8. 7.4.8 CreateListIterator (list)
        9. -
      9. 7.4.9 CreateEmptyIterator ( )
        10. -
      10. 7.4.10 CreateCompoundIterator ( iterator1, - iterator2 )
        11. -
      -
      5. -
    5. 7.5 Operations on Promise Objects -
        -
      1. 7.5.1 PromiseNew ( executor ) Abstract Operation
        2. -
      2. 7.5.2 PromiseBuiltinCapability () Abstract - Operation
        3. -
      3. 7.5.3 PromiseOf (value) Abstract Operation
        4. -
      4. 7.5.4 PromiseAll (promiseList) Abstract Operation
        5. -
      5. 7.5.5 PromiseCatch (promise, rejectedAction) Abstract - Operation
        6. -
      6. 7.5.6 PromiseThen (promise, resolvedAction, - rejectedAction) Abstract Operation
        7. -
      -
      6. -
    -
    9. -
  9. 8 Executable Code and Execution - Contexts -
      -
    1. 8.1 Lexical Environments -
        -
      1. 8.1.1 Environment Records
        2. -
      2. 8.1.2 Lexical Environment - Operations
        3. -
      -
      2. -
    2. 8.2 Code Realms -
        -
      1. 8.2.1 CreateRealm ( ) Abstract Operation
        2. -
      2. 8.2.2 CreateIntrinsics ( realmRec ) Abstract - Operation
        3. -
      3. 8.2.3 SetRealmGlobalObj ( realmRec, globalObj ) - Abstract Operation
        4. -
      4. 8.2.4 SetDefaultGlobalBindings ( realmRec - ) Abstract Operation
        5. -
      -
      3. -
    3. 8.3 Execution Contexts -
        -
      1. 8.3.1 ResolveBinding ( name ) Abstract - Operation
        2. -
      2. 8.3.2 GetThisEnvironment ( ) Abstract - Operation
        3. -
      3. 8.3.3 ResolveThisBinding ( ) Abstract - Operation
        4. -
      4. 8.3.4 GetGlobalObject ( ) Abstract Operation
        5. -
      -
      4. -
    4. 8.4 Tasks and Task Queues -
        -
      1. 8.4.1 EnqueueTask ( queueName, task, arguments) - Abstract Operation
        2. -
      2. 8.4.2 NextTask result
        3. -
      -
      5. -
    5. 8.5 Initialization -
        -
      1. 8.5.1 InitializeFirstRealm ( realm ) Abstract - Operation
        2. -
      -
      6. -
    -
    10. -
  10. 9 Ordinary and Exotic Objects - Behaviours -
      -
    1. 9.1 Ordinary Object - Internal Methods and Internal Slots -
        -
      1. 9.1.1 [[GetPrototypeOf]] - ( )
        2. -
      2. 9.1.2 - [[SetPrototypeOf]] (V)
        3. -
      3. 9.1.3 [[IsExtensible]] ( - )
        4. -
      4. 9.1.4 - [[PreventExtensions]] ( )
        5. -
      5. 9.1.5 - [[GetOwnProperty]] (P)
        6. -
      6. 9.1.6 - [[DefineOwnProperty]] (P, Desc)
        7. -
      7. 9.1.7 - [[HasProperty]](P)
        8. -
      8. 9.1.8 [[Get]] (P, - Receiver)
        9. -
      9. 9.1.9 [[Set]] ( P, V, - Receiver)
        10. -
      10. 9.1.10 - [[Delete]] (P)
        11. -
      11. 9.1.11 [[Enumerate]] ()
        12. -
      12. 9.1.12 - [[OwnPropertyKeys]] ( )
        13. -
      13. 9.1.13 ObjectCreate(proto, internalSlotsList) Abstract - Operation
        14. -
      14. 9.1.14 OrdinaryCreateFromConstructor - ( constructor, intrinsicDefaultProto, internalSlotsList )
        15. -
      -
      2. -
    2. 9.2 ECMAScript Function Objects -
        -
      1. 9.2.1 - [[GetOwnProperty]] (P)
        2. -
      2. 9.2.2 - [[Call]] ( thisArgument, argumentsList)
        3. -
      3. 9.2.3 [[Construct]] ( argumentsList)
        4. -
      4. 9.2.4 FunctionAllocate (functionPrototype, strict) - Abstract Operation
        5. -
      5. 9.2.5 FunctionInitialize (F, kind, Strict, - ParameterList, Body, Scope) Abstract Operation
        6. -
      6. 9.2.6 FunctionCreate (kind, ParameterList, Body, - Scope, Strict) Abstract Operation
        7. -
      7. 9.2.7 GeneratorFunctionCreate (kind, - ParameterList, Body, Scope, Strict) Abstract Operation
        8. -
      8. 9.2.8 - AddRestrictedFunctionProperties ( F, realm ) Abstract Operation
        9. -
      9. 9.2.9 MakeConstructor (F, writablePrototype, - prototype) Abstract Operation
        10. -
      10. 9.2.10 MakeMethod ( F, methodName, homeObject) Abstract - Operation
        11. -
      11. 9.2.11 SetFunctionName (F, name, prefix) Abstract - Operation
        12. -
      12. 9.2.12 CloneMethod(function, newHome, newName) Abstract - Operation
        13. -
      13. 9.2.13 - FunctionDeclarationInstantiation(func, argumentsList, env ) Abstract Operation
        14. -
      -
      3. -
    3. 9.3 Built-in Function Objects -
        -
      1. 9.3.1 - [[Call]] ( thisArgument, argumentsList)
        2. -
      2. 9.3.2 CreateBuiltinFunction(realm, steps, - prototype, internalSlotsList) Abstract Operation
        3. -
      -
      4. -
    4. 9.4 Built-in - Exotic Object Internal Methods and Data Fields -
        -
      1. 9.4.1 Bound Function Exotic - Objects
        2. -
      2. 9.4.2 Array Exotic Objects
        3. -
      3. 9.4.3 String Exotic Objects
        4. -
      4. 9.4.4 Arguments Exotic Objects
        5. -
      5. 9.4.5 Integer Indexed Exotic - Objects
        6. -
      6. 9.4.6 Module Exotic Objects
        7. -
      -
      5. -
    5. 9.5 Proxy Object - Internal Methods and Internal Slots -
        -
      1. 9.5.1 [[GetPrototypeOf]] ( - )
        2. -
      2. 9.5.2 [[SetPrototypeOf]] - (V)
        3. -
      3. 9.5.3 - [[IsExtensible]] ( )
        4. -
      4. 9.5.4 - [[PreventExtensions]] ( )
        5. -
      5. 9.5.5 [[GetOwnProperty]] - (P)
        6. -
      6. 9.5.6 - [[DefineOwnProperty]] (P, Desc)
        7. -
      7. 9.5.7 [[HasProperty]] - (P)
        8. -
      8. 9.5.8 [[Get]] (P, - Receiver)
        9. -
      9. 9.5.9 [[Set]] ( P, V, - Receiver)
        10. -
      10. 9.5.10 - [[Delete]] (P)
        11. -
      11. 9.5.11 - [[Enumerate]] ()
        12. -
      12. 9.5.12 [[OwnPropertyKeys]] - ( )
        13. -
      13. 9.5.13 - [[Call]] (thisArgument, argumentsList)
        14. -
      14. 9.5.14 [[Construct]] Internal Method
        15. -
      15. 9.5.15 ProxyCreate(target, handler) Abstract - Operation
        16. -
      -
      6. -
    -
    11. -
  11. 10 ECMAScript Language: Source Code -
      -
    1. 10.1 Source Text -
        -
      1. 10.1.1 Static Semantics: - UTF-16Encoding
        2. -
      2. 10.1.2 Static Semantics: UTF16Decode(lead, trail)
        3. -
      -
      2. -
    2. 10.2 Types of Source Code -
        -
      1. 10.2.1 Strict Mode Code
        2. -
      2. 10.2.2 Non-ECMAScript Functions
        3. -
      -
      3. -
    -
    12. -
  12. 11 ECMAScript Language: Lexical Grammar -
      -
    1. 11.1 Unicode Format-Control - Characters
      2. -
    2. 11.2 White Space
      3. -
    3. 11.3 Line Terminators
      4. -
    4. 11.4 Comments
      5. -
    5. 11.5 Tokens
      6. -
    6. 11.6 Names and Keywords -
        -
      1. 11.6.1 Identifier Names
        2. -
      2. 11.6.2 Reserved Words
        3. -
      -
      7. -
    7. 11.7 Punctuators
      8. -
    8. 11.8 Literals -
        -
      1. 11.8.1 Null Literals
        2. -
      2. 11.8.2 Boolean Literals
        3. -
      3. 11.8.3 Numeric Literals
        4. -
      4. 11.8.4 String Literals
        5. -
      5. 11.8.5 Regular Expression - Literals
        6. -
      6. 11.8.6 Template Literal Lexical - Components
        7. -
      -
      9. -
    9. 11.9 Automatic Semicolon Insertion -
        -
      1. 11.9.1 Rules of Automatic - Semicolon Insertion
        2. -
      2. 11.9.2 Examples of - Automatic Semicolon Insertion
        3. -
      -
      10. -
    -
    13. -
  13. 12 ECMAScript Language: Expressions -
      -
    1. 12.1 Identifiers -
        -
      1. 12.1.1 Static Semantics: - Early Errors
        2. -
      2. 12.1.2 Static Semantics: - BoundNames
        3. -
      3. 12.1.3 Static - Semantics: StringValue
        4. -
      4. 12.1.4 Runtime - Semantics: BindingInitialization
        5. -
      5. 12.1.5 Runtime Semantics: - Evaluation
        6. -
      -
      2. -
    2. 12.2 Primary Expression -
        -
      1. 12.2.0 Semantics
        2. -
      2. 12.2.1 The this Keyword
        3. -
      3. 12.2.2 Identifier Reference
        4. -
      4. 12.2.3 Literals
        5. -
      5. 12.2.4 Array Initializer
        6. -
      6. 12.2.5 Object Initializer
        7. -
      7. 12.2.6 Function Defining - Expressions
        8. -
      8. 12.2.7 Generator Comprehensions
        9. -
      9. 12.2.8 Regular - Expression Literals
        10. -
      10. 12.2.9 Template Literals
        11. -
      11. 12.2.10 The Grouping Operator
        12. -
      -
      3. -
    3. 12.3 Left-Hand-Side Expressions -
        -
      1. 12.3.1 Static - Semantics
        2. -
      2. 12.3.2 Property Accessors
        3. -
      3. 12.3.3 The new Operator
        4. -
      4. 12.3.4 Function Calls
        5. -
      5. 12.3.5 The super Keyword
        6. -
      6. 12.3.6 Argument Lists
        7. -
      7. 12.3.7 Tagged Templates
        8. -
      -
      4. -
    4. 12.4 Postfix Expressions -
        -
      1. 12.4.1 Static - Semantics: Early Errors
        2. -
      2. 12.4.2 - Static Semantics: IsFunctionDefinition
        3. -
      3. 12.4.3 Static Semantics: - IsValidSimpleAssignmentTarget
        4. -
      4. 12.4.4 Postfix Increment Operator
        5. -
      5. 12.4.5 Postfix Decrement Operator
        6. -
      -
      5. -
    5. 12.5 Unary Operators -
        -
      1. 12.5.1 Static - Semantics: Early Errors
        2. -
      2. 12.5.2 Static - Semantics: IsFunctionDefinition
        3. -
      3. 12.5.3 Static Semantics: - IsValidSimpleAssignmentTarget
        4. -
      4. 12.5.4 The delete Operator
        5. -
      5. 12.5.5 The void Operator
        6. -
      6. 12.5.6 The typeof Operator
        7. -
      7. 12.5.7 Prefix Increment Operator
        8. -
      8. 12.5.8 Prefix Decrement Operator
        9. -
      9. 12.5.9 Unary + Operator
        10. -
      10. 12.5.10 Unary - Operator
        11. -
      11. 12.5.11 Bitwise NOT Operator ( ~ - )
        12. -
      12. 12.5.12 Logical NOT Operator ( ! - )
        13. -
      -
      6. -
    6. 12.6 Multiplicative Operators -
        -
      1. 12.6.1 Static Semantics: - IsFunctionDefinition
        2. -
      2. 12.6.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.6.3 - Runtime Semantics: Evaluation
        4. -
      -
      7. -
    7. 12.7 Additive Operators -
        -
      1. 12.7.1 - Static Semantics: IsFunctionDefinition
        2. -
      2. 12.7.2 Static Semantics: - IsValidSimpleAssignmentTarget
        3. -
      3. 12.7.3 The Addition operator ( - + )
        4. -
      4. 12.7.4 The Subtraction Operator ( - - )
        5. -
      5. 12.7.5 Applying the - Additive Operators to Numbers
        6. -
      -
      8. -
    8. 12.8 Bitwise Shift Operators -
        -
      1. 12.8.1 Static Semantics: - IsFunctionDefinition
        2. -
      2. 12.8.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.8.3 The Left Shift Operator ( - << )
        4. -
      4. 12.8.4 The Signed Right Shift Operator - ( >> )
        5. -
      5. 12.8.5 The Unsigned Right Shift - Operator ( >>> )
        6. -
      -
      9. -
    9. 12.9 Relational Operators -
        -
      1. 12.9.1 - Static Semantics: IsFunctionDefinition
        2. -
      2. 12.9.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.9.3 Runtime - Semantics: Evaluation
        4. -
      4. 12.9.4 Runtime Semantics: InstanceofOperator(O, - C)
        5. -
      -
      10. -
    10. 12.10 Equality Operators -
        -
      1. 12.10.1 - Static Semantics: IsFunctionDefinition
        2. -
      2. 12.10.2 Static Semantics: - IsValidSimpleAssignmentTarget
        3. -
      3. 12.10.3 Runtime - Semantics: Evaluation
        4. -
      -
      11. -
    11. 12.11 Binary Bitwise Operators -
        -
      1. 12.11.1 Static Semantics: - IsFunctionDefinition
        2. -
      2. 12.11.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.11.3 - Runtime Semantics: Evaluation
        4. -
      -
      12. -
    12. 12.12 Binary Logical Operators -
        -
      1. 12.12.1 Static Semantics: - IsFunctionDefinition
        2. -
      2. 12.12.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.12.3 - Runtime Semantics: Evaluation
        4. -
      -
      13. -
    13. 12.13 Conditional Operator ( ? : ) -
        -
      1. 12.13.1 - Static Semantics: IsFunctionDefinition
        2. -
      2. 12.13.2 Static - Semantics: IsValidSimpleAssignmentTarget
        3. -
      3. 12.13.3 Runtime - Semantics: Evaluation
        4. -
      -
      14. -
    14. 12.14 Assignment Operators -
        -
      1. 12.14.1 Static - Semantics: Early Errors
        2. -
      2. 12.14.2 - Static Semantics: IsFunctionDefinition
        3. -
      3. 12.14.3 Static - Semantics: IsValidSimpleAssignmentTarget
        4. -
      4. 12.14.4 Runtime - Semantics: Evaluation
        5. -
      5. 12.14.5 Destructuring Assignment
        6. -
      -
      15. -
    15. 12.15 Comma Operator ( , ) -
        -
      1. 12.15.1 Static - Semantics: IsFunctionDefinition
        2. -
      2. 12.15.2 Static Semantics: - IsValidSimpleAssignmentTarget
        3. -
      3. 12.15.3 Runtime - Semantics: Evaluation
        4. -
      -
      16. -
    -
    14. -
  14. 13 ECMAScript Language: - Statements and Declarations -
      -
    1. 13.0 Statement Semantics -
        -
      1. 13.0.1 Static - Semantics: VarDeclaredNames
        2. -
      2. 13.0.2 - Static Semantics: VarScopedDeclarations
        3. -
      3. 13.0.3 - Runtime Semantics: LabelledEvaluation
        4. -
      4. 13.0.4 Runtime - Semantics: Evaluation
        5. -
      -
      2. -
    2. 13.1 Block -
        -
      1. 13.1.1 Static Semantics: Early - Errors
        2. -
      2. 13.1.2 Static - Semantics: LexicallyScopedDeclarations
        3. -
      3. 13.1.3 Static - Semantics: LexicallyDeclaredNames
        4. -
      4. 13.1.4 Static - Semantics: TopLevelLexicallyDeclaredNames
        5. -
      5. 13.1.5 Static - Semantics: TopLevelLexicallyScopedDeclarations
        6. -
      6. 13.1.6 Static Semantics: - TopLevelVarDeclaredNames
        7. -
      7. 13.1.7 Static - Semantics: TopLevelVarScopedDeclarations
        8. -
      8. 13.1.8 Static Semantics: - VarDeclaredNames
        9. -
      9. 13.1.9 Static - Semantics: VarScopedDeclarations
        10. -
      10. 13.1.10 Runtime Semantics: - Evaluation
        11. -
      11. 13.1.11 Runtime Semantics: - BlockDeclarationInstantiation( code, env )
        12. -
      -
      3. -
    3. 13.2 Declarations and the - Variable Statement -
        -
      1. 13.2.1 Let and Const Declarations
        2. -
      2. 13.2.2 Variable Statement
        3. -
      3. 13.2.3 Destructuring Binding - Patterns
        4. -
      -
      4. -
    4. 13.3 Empty Statement -
        -
      1. 13.3.1 Runtime - Semantics: Evaluation
        2. -
      -
      5. -
    5. 13.4 Expression Statement -
        -
      1. 13.4.1 Runtime - Semantics: Evaluation
        2. -
      -
      6. -
    6. 13.5 The if Statement -
        -
      1. 13.5.1 Static - Semantics: VarDeclaredNames
        2. -
      2. 13.5.2 Static - Semantics: VarScopedDeclarations
        3. -
      3. 13.5.3 Runtime Semantics: - Evaluation
        4. -
      -
      7. -
    7. 13.6 Iteration Statements -
        -
      1. 13.6.0 Semantics
        2. -
      2. 13.6.1 The do-while - Statement
        3. -
      3. 13.6.2 The while Statement
        4. -
      4. 13.6.3 The for Statement
        5. -
      5. 13.6.4 The - for-in and for-of Statements
        6. -
      -
      8. -
    8. 13.7 The continue Statement -
        -
      1. 13.7.1 Static - Semantics: Early Errors
        2. -
      2. 13.7.2 Runtime - Semantics: Evaluation
        3. -
      -
      9. -
    9. 13.8 The break Statement -
        -
      1. 13.8.1 Static - Semantics: Early Errors
        2. -
      2. 13.8.2 Runtime - Semantics: Evaluation
        3. -
      -
      10. -
    10. 13.9 The return Statement -
        -
      1. 13.9.1 Runtime - Semantics: Evaluation
        2. -
      -
      11. -
    11. 13.10 The with Statement -
        -
      1. 13.10.1 Static - Semantics: Early Errors
        2. -
      2. 13.10.2 Static - Semantics: VarDeclaredNames
        3. -
      3. 13.10.3 - Static Semantics: VarScopedDeclarations
        4. -
      4. 13.10.4 Runtime - Semantics: Evaluation
        5. -
      -
      12. -
    12. 13.11 The switch Statement -
        -
      1. 13.11.1 Static - Semantics: Early Errors
        2. -
      2. 13.11.2 Static Semantics: - LexicallyScopedDeclarations
        3. -
      3. 13.11.3 - Static Semantics: LexicallyDeclaredNames
        4. -
      4. 13.11.4 Static - Semantics: VarDeclaredNames
        5. -
      5. 13.11.5 - Static Semantics: VarScopedDeclarations
        6. -
      6. 13.11.6 Runtime Semantics: - CaseBlockEvaluation
        7. -
      7. 13.11.7 Runtime Semantics: - CaseSelectorEvaluation
        8. -
      8. 13.11.8 Runtime - Semantics: Evaluation
        9. -
      -
      13. -
    13. 13.12 Labelled Statements -
        -
      1. 13.12.1 Static - Semantics: Early Errors
        2. -
      2. 13.12.2 Static Semantics: - CurrentLabelSet
        3. -
      3. 13.12.3 - Static Semantics: VarDeclaredNames
        4. -
      4. 13.12.4 - Static Semantics: VarScopedDeclarations
        5. -
      5. 13.12.5 - Runtime Semantics: LabelledEvaluation
        6. -
      -
      14. -
    14. 13.13 The throw Statement -
        -
      1. 13.13.1 Runtime - Semantics: Evaluation
        2. -
      -
      15. -
    15. 13.14 The try Statement -
        -
      1. 13.14.1 Static - Semantics: Early Errors
        2. -
      2. 13.14.2 Static - Semantics: VarDeclaredNames
        3. -
      3. 13.14.3 Static - Semantics: VarScopedDeclarations
        4. -
      4. 13.14.4 - Runtime Semantics: BindingInitialization
        5. -
      5. 13.14.5 Runtime Semantics: - CatchClauseEvaluation
        6. -
      6. 13.14.6 Runtime - Semantics: Evaluation
        7. -
      -
      16. -
    16. 13.15 The debugger statement -
        -
      1. 13.15.1 Runtime - Semantics: Evaluation
        2. -
      -
      17. -
    -
    15. -
  15. 14 ECMAScript Language: Functions - and Classes -
      -
    1. 14.1 Function Definitions -
        -
      1. 14.1.1 Directive - Prologues and the Use Strict Directive
        2. -
      2. 14.1.2 Static - Semantics: Early Errors
        3. -
      3. 14.1.3 Static - Semantics: BoundNames
        4. -
      4. 14.1.4 Static - Semantics: Contains
        5. -
      5. 14.1.5 - Static Semantics: ContainsExpression
        6. -
      6. 14.1.6 - Static Semantics: ExpectedArgumentCount
        7. -
      7. 14.1.7 Static - Semantics: HasInitializer
        8. -
      8. 14.1.8 Static - Semantics: HasName
        9. -
      9. 14.1.9 Static Semantics: - IsAnonymousFunctionDefinition ( production) Abstract Operation
        10. -
      10. 14.1.10 - Static Semantics: IsConstantDeclaration
        11. -
      11. 14.1.11 - Static Semantics: IsFunctionDefinition
        12. -
      12. 14.1.12 - Static Semantics: IsSimpleParameterList
        13. -
      13. 14.1.13 Static - Semantics: IsStrict
        14. -
      14. 14.1.14 Static Semantics: - LexicallyScopedDeclarations
        15. -
      15. 14.1.15 Static Semantics: - LexicallyDeclaredNames
        16. -
      16. 14.1.16 - Static Semantics: ReferencesSuper
        17. -
      17. 14.1.17 - Static Semantics: VarDeclaredNames
        18. -
      18. 14.1.18 - Static Semantics: VarScopedDeclarations
        19. -
      19. 14.1.19 Runtime - Semantics: EvaluateBody
        20. -
      20. 14.1.20 Runtime - Semantics: IteratorBindingInitialization
        21. -
      21. 14.1.21 Runtime Semantics: - InstantiateFunctionObject
        22. -
      22. 14.1.22 Runtime - Semantics: Evaluation
        23. -
      -
      2. -
    2. 14.2 Arrow Function Definitions -
        -
      1. 14.2.1 - Static Semantics: Early Errors
        2. -
      2. 14.2.2 - Static Semantics: BoundNames
        3. -
      3. 14.2.3 Static - Semantics: Contains
        4. -
      4. 14.2.4 Static Semantics: - ContainsExpression
        5. -
      5. 14.2.5 Static Semantics: - CoveredFormalsList
        6. -
      6. 14.2.6 Static Semantics: - ExpectedArgumentCount
        7. -
      7. 14.2.7 - Static Semantics: HasInitializer
        8. -
      8. 14.2.8 Static - Semantics: HasName
        9. -
      9. 14.2.9 Static Semantics: - IsSimpleParameterList
        10. -
      10. 14.2.10 Static - Semantics: LexicallyScopedDeclarations
        11. -
      11. 14.2.11 Static - Semantics: LexicallyDeclaredNames
        12. -
      12. 14.2.12 - Static Semantics: ReferencesSuper
        13. -
      13. 14.2.13 Static Semantics: - VarDeclaredNames
        14. -
      14. 14.2.14 Static Semantics: - VarScopedDeclarations
        15. -
      15. 14.2.15 Runtime - Semantics: IteratorBindingInitialization
        16. -
      16. 14.2.16 - Runtime Semantics: EvaluateBody
        17. -
      17. 14.2.17 - Runtime Semantics: Evaluation
        18. -
      -
      3. -
    3. 14.3 Method Definitions -
        -
      1. 14.3.1 Static - Semantics: Early Errors
        2. -
      2. 14.3.2 - Static Semantics: ComputedPropertyContains
        3. -
      3. 14.3.3 - Static Semantics: ExpectedArgumentCount
        4. -
      4. 14.3.4 - Static Semantics: HasComputedPropertyKey
        5. -
      5. 14.3.5 Static - Semantics: PropName
        6. -
      6. 14.3.6 Static - Semantics: ReferencesSuper
        7. -
      7. 14.3.7 Static Semantics: - SpecialMethod
        8. -
      8. 14.3.8 Runtime Semantics: - DefineMethod
        9. -
      9. 14.3.9 Runtime Semantics: - PropertyDefinitionEvaluation
        10. -
      -
      4. -
    4. 14.4 Generator Function Definitions -
        -
      1. 14.4.1 - Static Semantics: Early Errors
        2. -
      2. 14.4.2 - Static Semantics: BoundNames
        3. -
      3. 14.4.3 Static - Semantics: ComputedPropertyContains
        4. -
      4. 14.4.4 - Static Semantics: Contains
        5. -
      5. 14.4.5 Static - Semantics: HasComputedPropertyKey
        6. -
      6. 14.4.6 - Static Semantics: HasName
        7. -
      7. 14.4.7 Static - Semantics: IsConstantDeclaration
        8. -
      8. 14.4.8 Static - Semantics: IsFunctionDefinition
        9. -
      9. 14.4.9 Static - Semantics: LexicallyDeclaredNames
        10. -
      10. 14.4.10 - Static Semantics: PropName
        11. -
      11. 14.4.11 Static Semantics: - ReferencesSuper
        12. -
      12. 14.4.12 Static Semantics: - VarDeclaredNames
        13. -
      13. 14.4.13 Static - Semantics: VarScopedDeclarations
        14. -
      14. 14.4.14 Runtime Semantics: - EvaluateBody
        15. -
      15. 14.4.15 Runtime - Semantics: InstantiateFunctionObject
        16. -
      16. 14.4.16 - Runtime Semantics: PropertyDefinitionEvaluation
        17. -
      17. 14.4.17 - Runtime Semantics: Evaluation
        18. -
      -
      5. -
    5. 14.5 Class Definitions -
        -
      1. 14.5.1 Static - Semantics: Early Errors
        2. -
      2. 14.5.2 Static - Semantics: BoundNames
        3. -
      3. 14.5.3 Static Semantics: - ConstructorMethod
        4. -
      4. 14.5.4 Static - Semantics: Contains
        5. -
      5. 14.5.5 - Static Semantics: ComputedPropertyContains
        6. -
      6. 14.5.6 Static Semantics: - HasName
        7. -
      7. 14.5.7 - Static Semantics: IsConstantDeclaration
        8. -
      8. 14.5.8 - Static Semantics: IsFunctionDefinition
        9. -
      9. 14.5.9 Static Semantics: IsStatic
        10. -
      10. 14.5.10 - Static Semantics: LexicallyDeclaredNames
        11. -
      11. 14.5.11 Static - Semantics: NonConstructorMethodDefinitions
        12. -
      12. 14.5.12 Static - Semantics: PrototypePropertyNameList
        13. -
      13. 14.5.13 Static - Semantics: PropName
        14. -
      14. 14.5.14 Static Semantics: - StaticPropertyNameList
        15. -
      15. 14.5.15 Static - Semantics: VarDeclaredNames
        16. -
      16. 14.5.16 Runtime - Semantics: ClassDefinitionEvaluation
        17. -
      17. 14.5.17 Runtime - Semantics: Evaluation
        18. -
      -
      6. -
    6. 14.6 Tail Position Calls -
        -
      1. 14.6.1 Static Semantics: - IsInTailPosition(nonterminal) Abstract Operation
        2. -
      2. 14.6.2 Static - Semantics: HasProductionInTailPosition
        3. -
      3. 14.6.3 Runtime Semantics: PrepareForTailCall ( - )
        4. -
      -
      7. -
    -
    16. -
  16. 15 ECMAScript Language: Scripts and - Modules -
      -
    1. 15.1 Scripts -
        -
      1. 15.1.1 Static Semantics: - Early Errors
        2. -
      2. 15.1.2 Static Semantics: - IsStrict
        3. -
      3. 15.1.3 Static - Semantics: LexicallyDeclaredNames
        4. -
      4. 15.1.4 Static - Semantics: LexicallyScopedDeclarations
        5. -
      5. 15.1.5 Static Semantics: - VarDeclaredNames
        6. -
      6. 15.1.6 Static - Semantics: VarScopedDeclarations
        7. -
      7. 15.1.7 Runtime Semantics: - ScriptEvaluation
        8. -
      8. 15.1.8 Runtime - Semantics: GlobalDeclarationInstantiation
        9. -
      9. 15.1.9 Runtime Semantics: ScriptEvaluationTask - ( source )
        10. -
      -
      2. -
    2. 15.2 Modules -
        -
      1. 15.2.0 Module Static Semantics
        2. -
      2. 15.2.1 Imports
        3. -
      3. 15.2.2 Exports
        4. -
      4. 15.2.3 Runtime Semantics: Loader - State
        5. -
      5. 15.2.4 Runtime Semantics: Module - Loading
        6. -
      6. 15.2.5 Runtime Semantics: Module - Linking
        7. -
      7. 15.2.6 Runtime Semantics: - Module Evaluation
        8. -
      -
      3. -
    -
    17. -
  17. 16 Error Handling and Language - Extensions
    18. -
  18. 17 ECMAScript Standard Built-in - Objects
    19. -
  19. 18 The Global Object -
      -
    1. 18.1 Value Properties of the - Global Object -
        -
      1. 18.1.1 Infinity
        2. -
      2. 18.1.2 NaN
        3. -
      3. 18.1.3 undefined
        4. -
      -
      2. -
    2. 18.2 Function Properties of - the Global Object -
        -
      1. 18.2.1 eval (x)
        2. -
      2. 18.2.2 isFinite (number)
        3. -
      3. 18.2.3 isNaN (number)
        4. -
      4. 18.2.4 parseFloat (string)
        5. -
      5. 18.2.5 parseInt (string , radix)
        6. -
      6. 18.2.6 URI Handling Functions
        7. -
      -
      3. -
    3. 18.3 Constructor Properties - of the Global Object -
        -
      1. 18.3.1 Array ( . - . . )
        2. -
      2. 18.3.2 - ArrayBuffer ( . . . )
        3. -
      3. 18.3.3 Boolean - ( . . . )
        4. -
      4. 18.3.4 - DataView ( . . . )
        5. -
      5. 18.3.5 Date ( . . - . )
        6. -
      6. 18.3.6 Error ( . - . . )
        7. -
      7. 18.3.7 - EvalError ( . . . )
        8. -
      8. 18.3.8 Float32Array ( . . . )
        9. -
      9. 18.3.9 Float64Array ( . . . )
        10. -
      10. 18.3.10 - Function ( . . . )
        11. -
      11. 18.3.11 Int8Array ( . . . )
        12. -
      12. 18.3.12 Int16Array ( . . . )
        13. -
      13. 18.3.13 Int32Array ( . . . )
        14. -
      14. 18.3.14 Map ( . . . )
        15. -
      15. 18.3.15 Number ( - . . . )
        16. -
      16. 18.3.16 Object ( - . . . )
        17. -
      17. 18.3.17 - RangeError ( . . . )
        18. -
      18. 18.3.18 - ReferenceError ( . . . )
        19. -
      19. 18.3.19 RegExp ( - . . . )
        20. -
      20. 18.3.20 Set ( . . . )
        21. -
      21. 18.3.21 String ( - . . . )
        22. -
      22. 18.3.22 Symbol ( - . . . )
        23. -
      23. 18.3.23 - SyntaxError ( . . . )
        24. -
      24. 18.3.24 - TypeError ( . . . )
        25. -
      25. 18.3.25 Uint8Array ( . . . )
        26. -
      26. 18.3.26 Uint8ClampedArray ( . . . )
        27. -
      27. 18.3.27 Uint16Array ( . . . )
        28. -
      28. 18.3.28 Uint32Array ( . . . )
        29. -
      29. 18.3.29 - URIError ( . . . )
        30. -
      30. 18.3.30 WeakMap - ( . . . )
        31. -
      31. 18.3.31 WeakSet - ( . . . )
        32. -
      -
      4. -
    4. 18.4 Other Properties of the - Global Object -
        -
      1. 18.4.1 JSON
        2. -
      2. 18.4.2 Math
        3. -
      3. 18.4.3 Proxy ( . . . - )
        4. -
      4. 18.4.4 Reflect
        5. -
      5. 18.4.5 System
        6. -
      -
      5. -
    -
    20. -
  20. 19 Fundamental Objects -
      -
    1. 19.1 Object Objects -
        -
      1. 19.1.1 The Object Constructor
        2. -
      2. 19.1.2 Properties of the - Object Constructor
        3. -
      3. 19.1.3 Properties of the - Object Prototype Object
        4. -
      4. 19.1.4 Properties of Object - Instances
        5. -
      -
      2. -
    2. 19.2 Function Objects -
        -
      1. 19.2.1 The Function Constructor
        2. -
      2. 19.2.2 Properties of the - Function Constructor
        3. -
      3. 19.2.3 Properties of - the Function Prototype Object
        4. -
      4. 19.2.4 Function Instances
        5. -
      -
      3. -
    3. 19.3 Boolean Objects -
        -
      1. 19.3.1 The Boolean Constructor
        2. -
      2. 19.3.2 Properties of the - Boolean Constructor
        3. -
      3. 19.3.3 Properties of the - Boolean Prototype Object
        4. -
      4. 19.3.4 Properties of Boolean - Instances
        5. -
      -
      4. -
    4. 19.4 Symbol Objects -
        -
      1. 19.4.1 The Symbol Constructor
        2. -
      2. 19.4.2 Properties of the - Symbol Constructor
        3. -
      3. 19.4.3 Properties of the - Symbol Prototype Object
        4. -
      4. 19.4.4 Properties of Symbol - Instances
        5. -
      -
      5. -
    5. 19.5 Error Objects -
        -
      1. 19.5.1 The Error Constructor
        2. -
      2. 19.5.2 Properties of the Error - Constructor
        3. -
      3. 19.5.3 Properties of the - Error Prototype Object
        4. -
      4. 19.5.4 Properties of Error - Instances
        5. -
      5. 19.5.5 Native Error Types - Used in This Standard
        6. -
      6. 19.5.6 NativeError Object - Structure
        7. -
      -
      6. -
    -
    21. -
  21. 20 Numbers and Dates -
      -
    1. 20.1 Number Objects -
        -
      1. 20.1.1 The Number Constructor
        2. -
      2. 20.1.2 Properties of the - Number Constructor
        3. -
      3. 20.1.3 Properties of the - Number Prototype Object
        4. -
      4. 20.1.4 Properties of Number - Instances
        5. -
      -
      2. -
    2. 20.2 The Math Object -
        -
      1. 20.2.1 Value Properties of the - Math Object
        2. -
      2. 20.2.2 Function Properties - of the Math Object
        3. -
      -
      3. -
    3. 20.3 Date Objects -
        -
      1. 20.3.1 Overview of Date - Objects and Definitions of Abstract Operations
        2. -
      2. 20.3.2 The Date Constructor
        3. -
      3. 20.3.3 Properties of the Date - Constructor
        4. -
      4. 20.3.4 Properties of the - Date Prototype Object
        5. -
      5. 20.3.5 Properties of Date - Instances
        6. -
      -
      4. -
    -
    22. -
  22. 21 Text Processing -
      -
    1. 21.1 String Objects -
        -
      1. 21.1.1 The String Constructor
        2. -
      2. 21.1.2 Properties of the - String Constructor
        3. -
      3. 21.1.3 Properties of the - String Prototype Object
        4. -
      4. 21.1.4 Properties of String - Instances
        5. -
      5. 21.1.5 String Iterator Objects
        6. -
      -
      2. -
    2. 21.2 RegExp (Regular Expression) - Objects -
        -
      1. 21.2.1 Patterns
        2. -
      2. 21.2.2 Pattern Semantics
        3. -
      3. 21.2.3 The RegExp Constructor
        4. -
      4. 21.2.4 Properties of the - RegExp Constructor
        5. -
      5. 21.2.5 Properties of the - RegExp Prototype Object
        6. -
      6. 21.2.6 Properties of RegExp - Instances
        7. -
      -
      3. -
    -
    23. -
  23. 22 Indexed Collections -
      -
    1. 22.1 Array Objects -
        -
      1. 22.1.1 The Array Constructor
        2. -
      2. 22.1.2 Properties of the Array - Constructor
        3. -
      3. 22.1.3 Properties of the - Array Prototype Object
        4. -
      4. 22.1.4 Properties of Array - Instances
        5. -
      5. 22.1.5 Array Iterator Objects
        6. -
      -
      2. -
    2. 22.2 TypedArray Objects -
        -
      1. 22.2.1 The %TypedArray% Intrinsic - Object
        2. -
      2. 22.2.2 Properties - of the %TypedArray% Intrinsic Object
        3. -
      3. 22.2.3 Properties of - the %TypedArrayPrototype% Object
        4. -
      4. 22.2.4 The TypedArray - Constructors
        5. -
      5. 22.2.5 Properties of the - TypedArray Constructors
        6. -
      6. 22.2.6 Properties of - TypedArray Prototype Objects
        7. -
      7. 22.2.7 Properties of - TypedArray Instances
        8. -
      -
      3. -
    -
    24. -
  24. 23 Keyed Collection -
      -
    1. 23.1 Map Objects -
        -
      1. 23.1.1 The Map Constructor
        2. -
      2. 23.1.2 Properties of the Map - Constructor
        3. -
      3. 23.1.3 Properties of the Map - Prototype Object
        4. -
      4. 23.1.4 Properties of Map Instances
        5. -
      5. 23.1.5 Map Iterator Objects
        6. -
      -
      2. -
    2. 23.2 Set Objects -
        -
      1. 23.2.1 The Set Constructor
        2. -
      2. 23.2.2 Properties of the Set - Constructor
        3. -
      3. 23.2.3 Properties of the Set - Prototype Object
        4. -
      4. 23.2.4 Properties of Set Instances
        5. -
      5. 23.2.5 Set Iterator Objects
        6. -
      -
      3. -
    3. 23.3 WeakMap Objects -
        -
      1. 23.3.1 The WeakMap Constructor
        2. -
      2. 23.3.2 Properties of the - WeakMap Constructor
        3. -
      3. 23.3.3 Properties of the - WeakMap Prototype Object
        4. -
      4. 23.3.4 Properties of WeakMap - Instances
        5. -
      -
      4. -
    4. 23.4 WeakSet Objects -
        -
      1. 23.4.1 The WeakSet Constructor
        2. -
      2. 23.4.2 Properties of the - WeakSet Constructor
        3. -
      3. 23.4.3 Properties of the - WeakSet Prototype Object
        4. -
      4. 23.4.4 Properties of WeakSet - Instances
        5. -
      -
      5. -
    -
    25. -
  25. 24 Structured Data -
      -
    1. 24.1 ArrayBuffer Objects -
        -
      1. 24.1.1 Abstract - Operations For ArrayBuffer Objects
        2. -
      2. 24.1.2 The ArrayBuffer Constructor
        3. -
      3. 24.1.3 Properties of the - ArrayBuffer Constructor
        4. -
      4. 24.1.4 Properties of - the ArrayBuffer Prototype Object
        5. -
      5. 24.1.5 Properties of the - ArrayBuffer Instances
        6. -
      -
      2. -
    2. 24.2 DataView Objects -
        -
      1. 24.2.1 Abstract Operations - For DataView Objects
        2. -
      2. 24.2.2 The DataView Constructor
        3. -
      3. 24.2.3 Properties of the - DataView Constructor
        4. -
      4. 24.2.4 Properties of - the DataView Prototype Object
        5. -
      5. 24.2.5 Properties of DataView - Instances
        6. -
      -
      3. -
    3. 24.3 The JSON Object -
        -
      1. 24.3.1 JSON.parse ( text [ , reviver ] )
        2. -
      2. 24.3.2 JSON.stringify ( value [ , replacer [ , space - ] ] )
        3. -
      3. 24.3.3 JSON [ @@toStringTag ]
        4. -
      -
      4. -
    -
    26. -
  26. 25 Control Abstraction Objects -
      -
    1. 25.1 Common Iteration Interfaces -
        -
      1. 25.1.1 The Iterable Interface
        2. -
      2. 25.1.2 The Iterator Interface
        3. -
      3. 25.1.3 The IteratorResult - Interface
        4. -
      -
      2. -
    2. 25.2 GeneratorFunction Objects -
        -
      1. 25.2.1 The GeneratorFunction - Constructor
        2. -
      2. 25.2.2 Properties - of the GeneratorFunction Constructor
        3. -
      3. 25.2.3 - Properties of the GeneratorFunction Prototype Object
        4. -
      4. 25.2.4 GeneratorFunction Instances
        5. -
      -
      3. -
    3. 25.3 Generator Objects -
        -
      1. 25.3.1 Properties of Generator - Prototype
        2. -
      2. 25.3.2 Properties of Generator - Instances
        3. -
      3. 25.3.3 Generator Abstract - Operations
        4. -
      -
      4. -
    4. 25.4 Promise Objects -
        -
      1. 25.4.1 Promise Abstract Operations
        2. -
      2. 25.4.2 Promise Tasks
        3. -
      3. 25.4.3 The Promise Constructor
        4. -
      4. 25.4.4 Properties of the - Promise Constructor
        5. -
      5. 25.4.5 Properties of the - Promise Prototype Object
        6. -
      6. 25.4.6 Properties of Promise - Instances
        7. -
      -
      5. -
    -
    27. -
  27. 26 Reflection -
      -
    1. 26.1 The Reflect Object -
        -
      1. 26.1.1 Reflect.apply ( target, thisArgument, - argumentsList )
        2. -
      2. 26.1.2 Reflect.construct ( target, argumentsList - )
        3. -
      3. 26.1.3 Reflect.defineProperty ( target, - propertyKey, attributes )
        4. -
      4. 26.1.4 Reflect.deleteProperty ( target, - propertyKey )
        5. -
      5. 26.1.5 Reflect.enumerate ( target )
        6. -
      6. 26.1.6 Reflect.get ( target, propertyKey [ , receiver - ])
        7. -
      7. 26.1.7 - Reflect.getOwnPropertyDescriptor ( target, propertyKey )
        8. -
      8. 26.1.8 Reflect.getPrototypeOf ( target - )
        9. -
      9. 26.1.9 Reflect.has ( target, propertyKey )
        10. -
      10. 26.1.10 Reflect.isExtensible (target)
        11. -
      11. 26.1.11 Reflect.ownKeys ( target )
        12. -
      12. 26.1.12 Reflect.preventExtensions ( - target )
        13. -
      13. 26.1.13 Reflect.set ( target, propertyKey, V [ , - receiver ] )
        14. -
      14. 26.1.14 Reflect.setPrototypeOf ( target, - proto )
        15. -
      -
      2. -
    2. 26.2 Realm Objects -
        -
      1. 26.2.1 The Reflect.Realm Constructor
        2. -
      2. 26.2.2 Properties of - the Reflect.Realm Constructor
        3. -
      3. 26.2.3 Properties - of the Reflect.Realm Prototype Object
        4. -
      4. 26.2.4 Properties of - Reflect.Realm Instances
        5. -
      -
      3. -
    3. 26.3 Loader Objects -
        -
      1. 26.3.1 The Reflect.Loader - Constructor
        2. -
      2. 26.3.2 Properties of the - Loader Constructor
        3. -
      3. 26.3.3 Properties - of the Reflect.Loader Prototype Object
        4. -
      4. 26.3.4 Properties of - Reflect.Loader Instances
        5. -
      5. 26.3.5 Loader Iterator Objects
        6. -
      -
      4. -
    4. 26.4 The System Object
      5. -
    5. 26.5 Proxy Objects -
        -
      1. 26.5.1 The Proxy Constructor - Function
        2. -
      2. 26.5.2 Properties of - the Proxy Constructor Function
        3. -
      -
      6. -
    -
    28. -
  28. Annex A (informative) Grammar Summary -
      -
    1. A.1 Lexical Grammar -
        -
      1. Expressions
        2. -
      2. Statements
        3. -
      3. Functions and Scripts
        4. -
      4. Number Conversions
        5. -
      5. Universal Resource Identifier Character Classes
        6. -
      6. Regular Expressions
        7. -
      -
      2. -
    -
    29. -
  29. Annex B (normative) Additional ECMAScript Features for Web Browsers -
      -
    1. B.1 Additional Syntax -
        -
      1. B.1.1 Numeric Literals
        2. -
      2. B.1.2 String Literals
        3. -
      3. B.1.3 HTML-like Comments
        4. -
      4. B.1.4 Regular Expressions - Patterns
        5. -
      -
      2. -
    2. B.2 Additional Built-in Properties -
        -
      1. B.2.1 Additional - Properties of the Global Object
        2. -
      2. B.2.2 - Additional Properties of the Object.prototype Object
        3. -
      3. B.2.3 - Additional Properties of the String.prototype Object
        4. -
      4. B.2.4 Additional - Properties of the Date.prototype Object
        5. -
      5. B.2.5 - Additional Properties of the RegExp.prototype Object
        6. -
      -
      3. -
    3. B.3 Other Additional Features -
        -
      1. B.3.1 __proto__ - Property Names in Object Initializers
        2. -
      2. B.3.2 Web Legacy - Compatibility for Block-Level Function Declarations
        3. -
      3. B.3.3 VariableStatements in - Catch blocks
        4. -
      -
      4. -
    -
    30. -
  30. Annex C (informative) The Strict Mode of ECMAScript
    31. -
  31. Annex D - (informative) Corrections and Clarifications That May Introduce Incompatibilities with - Prior Editions -
      -
    1. D.1 - In the 6th Edition
      2. -
    2. D.2 - In the 5th Edition
      3. -
    -
    32. -
  32. Annex E (informative) Additions and Changes that Introduce Incompatibilities with Prior Editions -
      -
    1. E.1 - In the 6th Edition
      2. -
    2. E.2 - In the 5th Edition
      3. -
    -
    33. -
  33. Bibliography
    34. -
-
- -
-

Introduction

- -

This Ecma Standard is based on several originating technologies, the most well known being JavaScript (Netscape) and JScript - (Microsoft). The language was invented by Brendan Eich at Netscape and first appeared in that company’s Navigator 2.0 - browser. It has appeared in all subsequent browsers from Netscape and in all browsers from Microsoft starting with Internet - Explorer 3.0.

- -

The development of this Standard started in November 1996. The first edition of this Ecma Standard was adopted by the Ecma - General Assembly of June 1997.

- -

That Ecma Standard was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international - standard ISO/IEC 16262, in April 1998. The Ecma General Assembly of June 1998 approved the second edition of ECMA-262 to keep it - fully aligned with ISO/IEC 16262. Changes between the first and the second edition are editorial in nature.

- -

The third edition of the Standard introduced powerful regular expressions, better string handling, new control statements, - try/catch exception handling, tighter definition of errors, formatting for numeric output and minor changes in anticipation of - forthcoming internationalisation facilities and future language growth. The third edition of the ECMAScript standard was adopted - by the Ecma General Assembly of December 1999 and published as ISO/IEC 16262:2002 in June 2002.

- -

After publication of the third edition, ECMAScript achieved massive adoption in conjunction with the World Wide Web where it - has become the programming language that is supported by essentially all web browsers. Significant work was done to develop a - fourth edition of ECMAScript. Although that work was not completed and not published as the fourth edition of ECMAScript, it - informs continuing evolution of the language. The fifth edition of ECMAScript (published as ECMA-262 5th edition) - codified de facto interpretations of the language specification that have become common among browser implementations and added - support for new features that had emerged since the publication of the third edition. Such features include accessor properties, - reflective creation and inspection of objects, program control of property attributes, additional array manipulation functions, - support for the JSON object encoding format, and a strict mode that provides enhanced error checking and program security.

- -

The edition 5.1 of the ECMAScript Standard is fully aligned with the third edition of the international standard ISO/IEC - 16262:2011.

- -

This present sixth edition of the Standard………

- -

ECMAScript is a vibrant language and the evolution of the language is not complete. Significant technical enhancement will - continue with future editions of this specification.

- -

This Ecma Standard has been adopted by the General Assembly of <month> <year>.

- -

"DISCLAIMER

- -

This draft document may be copied and furnished to others, and derivative works that comment on or otherwise explain it or - assist in its implementation may be prepared, copied, published, and distributed, in whole or in part, without restriction of - any kind, provided that the above copyright notice and this section are included on all such copies and derivative works. - However, this document itself may not be modified in any way, including by removing the copyright notice or references to Ecma - International, except as needed for the purpose of developing any document or deliverable produced by Ecma - International.

- -

This disclaimer is valid only prior to final version of this document. After approval all rights on the standard are - reserved by Ecma International.

- -

The limited permissions are granted through the standardization phase and will not be revoked by Ecma International or its - successors or assigns during this time.

- -

This document and the information contained herein is provided on an "AS IS" basis and ECMA INTERNATIONAL DISCLAIMS ALL - WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT - INFRINGE ANY OWNERSHIP RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

-
- -
ECMAScript Language Specification
- -
-

1 Scope

- -

This Standard defines the ECMAScript scripting language.

-
- -
-

2 Conformance

- -

A conforming implementation of ECMAScript must provide and support all the types, values, objects, properties, functions, and - program syntax and semantics described in this specification.

- -

A conforming implementation of ECMAScript must interpret characters in conformance with the Unicode Standard, Version 5.1.0 - or later and ISO/IEC 10646. If the adopted ISO/IEC 10646-1 subset is not otherwise specified, it is presumed to be the Unicode - set, collection 10646.

- -

A conforming implementation of ECMAScript that provides an application programming interface that supports programs that need - to adapt to the linguistic and cultural conventions used by different human languages and countries must implement the interface - defined by the most recent edition of ECMA-402 that is compatible with this specification.

- -

A conforming implementation of ECMAScript may provide additional types, values, objects, properties, and functions beyond - those described in this specification. In particular, a conforming implementation of ECMAScript may provide properties not - described in this specification, and values for those properties, for objects that are described in this specification.

- -

A conforming implementation of ECMAScript may support program and regular expression syntax not described in this - specification. In particular, a conforming implementation of ECMAScript may support program syntax that makes use of the - “future reserved words” listed in subclause 11.6.2.2 of this - specification.

-
- -
-

3 Normative - references

- -

The following referenced documents are indispensable for the application of this document. For dated references, only the - edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) - applies.

- -

IEEE Std 754-2008: IEEE Standard for Floating-Point Arithmetic. Institute of Electrical and - Electronic Engineers, New York (2008)

- -

ISO/IEC 10646:2003: Information Technology – Universal Multiple-Octet Coded Character Set - (UCS) plus Amendment 1:2005, Amendment 2:2006, Amendment 3:2008, and Amendment 4:2008, plus additional amendments and - corrigenda, or successor

- -

The Unicode Standard, Version 5.0, as amended by Unicode 5.1.0, or successor

- -

Unicode Standard Annex #15, Unicode Normalization Forms, version Unicode 5.1.0, or - successor

- -

Unicode Standard Annex #31, Unicode Identifiers and Pattern Syntax, version Unicode 5.1.0, or - successor.

- -

ECMA-402, ECMAScript Internationalization API Specification.
http://www.ecma-international.org/publications/standards/Ecma-402.htm

- -

ECMA-404, The JSON Data Interchange Format.
http://www.ecma-international.org/publications/standards/Ecma-404.htm

-
- -
-
-

4 Overview

- -

This section contains a non-normative overview of the ECMAScript language.

- -

ECMAScript is an object-oriented programming language for performing computations and manipulating computational objects - within a host environment. ECMAScript as defined here is not intended to be computationally self-sufficient; indeed, there are - no provisions in this specification for input of external data or output of computed results. Instead, it is expected that the - computational environment of an ECMAScript program will provide not only the objects and other facilities described in this - specification but also certain environment-specific objects, whose description and behaviour are beyond the scope of this - specification except to indicate that they may provide certain properties that can be accessed and certain functions that can - be called from an ECMAScript program.

- -

A scripting language is a programming language that is used to manipulate, customize, and automate the - facilities of an existing system. In such systems, useful functionality is already available through a user interface, and the - scripting language is a mechanism for exposing that functionality to program control. In this way, the existing system is said - to provide a host environment of objects and facilities, which completes the capabilities of the scripting language. A - scripting language is intended for use by both professional and non-professional programmers. ECMAScript was originally - designed to be used as a scripting language, but has become widely used as a general purpose programming language.

- -

ECMAScript was originally designed to be a Web scripting language, providing a mechanism to enliven Web pages - in browsers and to perform server computation as part of a Web-based client-server architecture. ECMAScript is now used both - as a general propose programming language and to provide core scripting capabilities for a variety of host environments. - Therefore the core language is specified in this document apart from any particular host environment.

- -

Some of the facilities of ECMAScript are similar to those used in other programming languages; in particular C, - Java™, Self, and Scheme as described in:

- -

ISO/IEC 9899:1996, Programming Languages – C.

- -

Gosling, James, Bill Joy and Guy Steele. The Java™ Language - Specification. Addison Wesley Publishing Co., 1996.

- -

Ungar, David, and Smith, Randall B. Self: The Power of Simplicity. - OOPSLA '87 Conference Proceedings, pp. 227–241, Orlando, FL, October 1987.

- -

IEEE Standard for the Scheme Programming Language. IEEE Std - 1178-1990.

-
- -
-

4.1 Web - Scripting

- -

A web browser provides an ECMAScript host environment for client-side computation including, for instance, objects that - represent windows, menus, pop-ups, dialog boxes, text areas, anchors, frames, history, cookies, and input/output. Further, the - host environment provides a means to attach scripting code to events such as change of focus, page and image loading, - unloading, error and abort, selection, form submission, and mouse actions. Scripting code appears within the HTML and the - displayed page is a combination of user interface elements and fixed and computed text and images. The scripting code is - reactive to user interaction and there is no need for a main program.

- -

A web server provides a different host environment for server-side computation including objects representing requests, - clients, and files; and mechanisms to lock and share data. By using browser-side and server-side scripting together, it is - possible to distribute computation between the client and server while providing a customized user interface for a Web-based - application.

- -

Each Web browser and server that supports ECMAScript supplies its own host environment, completing the ECMAScript execution - environment.

-
- -
-
-

4.2 - ECMAScript Overview

- -

The following is an informal overview of ECMAScript—not all parts of the language are described. This overview is - not part of the standard proper.

- -

ECMAScript is object-based: basic language and host facilities are provided by objects, and an ECMAScript program is a - cluster of communicating objects. In ECMAScript, an object is a collection of properties each - with zero or more attributes that determine how each property can be used—for example, when the Writable - attribute for a property is set to false, any attempt by executed ECMAScript code to change the value of the property - fails. Properties are containers that hold other objects, primitive values, or functions. A - primitive value is a member of one of the following built-in types: Undefined, Null, Boolean, - Number, Symbol and String; an object is a member of the remaining built-in type Object; and a - function is a callable object. A function that is associated with an object via a property is a method.

- -

ECMAScript defines a collection of built-in objects that round out the definition of ECMAScript entities. - These built-in objects include the global object, the Object object, the Function object, the Array - object, the String object, the Boolean object, the Number object, the Math object, the - Date object, the RegExp object, the JSON object, and the Error objects Error, EvalError, - RangeError, ReferenceError, SyntaxError, TypeError and URIError.

- -

ECMAScript also defines a set of built-in operators. ECMAScript operators include various unary operations, - multiplicative operators, additive operators, bitwise shift operators, relational operators, equality operators, binary - bitwise operators, binary logical operators, assignment operators, and the comma operator.

- -

ECMAScript syntax intentionally resembles Java syntax. ECMAScript syntax is relaxed to enable it to serve as an - easy-to-use scripting language. For example, a variable is not required to have its type declared nor are types associated - with properties, and defined functions are not required to have their declarations appear textually before calls to - them.

-
- -
-

4.2.1 Objects

- -

ECMAScript objects are not fundamentally class-based such as those in C++, Smalltalk, or Java. Instead objects may be - created in various ways including via a literal notation or via constructors which create objects and then - execute code that initializes all or part of them by assigning initial values to their properties. Each constructor is a - function that has a property named “prototype” that is used to implement prototype-based - inheritance and shared properties. Objects are created by using constructors in new - expressions; for example, new Date(2009,11) creates a new Date object. Invoking a constructor without using - new has consequences that depend on the constructor. For example, Date() produces a string - representation of the current date and time rather than an object.

- -

Every object created by a constructor has an implicit reference (called the object’s prototype) to the value - of its constructor’s “prototype” property. Furthermore, a prototype may have a non-null - implicit reference to its prototype, and so on; this is called the prototype chain. When a reference is made to a - property in an object, that reference is to the property of that name in the first object in the prototype chain that - contains a property of that name. In other words, first the object mentioned directly is examined for such a property; if - that object contains the named property, that is the property to which the reference refers; if that object does not contain - the named property, the prototype for that object is examined next; and so on.

- -
- - An image of lots of boxes and arrows. - -
Figure 1 — Object/Prototype Relationships
-
- -

In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and - inheritance is only of structure and behaviour. In ECMAScript, the state and methods are carried by objects, while - structure, behaviour, and state are all inherited.

- -

All objects that do not directly contain a particular property that their prototype contains share that property and its - value. Figure 1 illustrates this:

- -

CF is a constructor (and also an object). Five objects have been created by using new expressions: - cf1, cf2, cf3, cf4, and cf5. Each - of these objects contains properties named q1 and q2. The dashed lines represent the implicit - prototype relationship; so, for example, cf3’s prototype is CFp. The constructor, - CF, has two properties itself, named P1 and P2, which are not visible to - CFp, cf1, cf2, cf3, cf4, or - cf5. The property named CFP1 in CFp is shared by cf1, - cf2, cf3, cf4, and cf5 (but not by CF), as - are any properties found in CFp’s implicit prototype chain that are not named q1, - q2, or CFP1. Notice that there is no implicit prototype link between CF and - CFp.

- -

Unlike most class-based object languages, properties can be added to objects dynamically by assigning values to them. - That is, constructors are not required to name or assign values to all or any of the constructed object’s properties. - In the above diagram, one could add a new shared property for cf1, cf2, - cf3, cf4, and cf5 by assigning a new value to the property in - CFp.

- -

Although ECMAScript objects are not inherently class-based, it is often convenient to define class-like abstractions - based upon a common pattern of constructor functions, prototype objects, and methods. The ECMAScript built-in object - themselves follow such a class-like pattern. The ECMAScript language includes syntatic class definitions that permit - programmers to concisely define objects that conform to the same class-like abstraction pattern used by the built-in - objects.

-
- -
-

4.2.2 The Strict Variant of ECMAScript

- -

The ECMAScript Language recognizes the possibility that some users of the language may wish to restrict their usage of - some features available in the language. They might do so in the interests of security, to avoid what they consider to be - error-prone features, to get enhanced error checking, or for other reasons of their choosing. In support of this - possibility, ECMAScript defines a strict variant of the language. The strict variant of the language excludes some specific - syntactic and semantic features of the regular ECMAScript language and modifies the detailed semantics of some features. The - strict variant also specifies additional error conditions that must be reported by throwing error exceptions in situations - that are not specified as errors by the non-strict form of the language.

- -

The strict variant of ECMAScript is commonly referred to as the strict mode of the language. Strict mode selection - and use of the strict mode syntax and semantics of ECMAScript is explicitly made at the level of individual ECMAScript code - units. Because strict mode is selected at the level of a syntactic code unit, strict mode only imposes restrictions that - have local effect within such a code unit. Strict mode does not restrict or modify any aspect of the ECMAScript semantics - that must operate consistently across multiple code units. A complete ECMAScript program may be composed for both strict - mode and non-strict mode ECMAScript code units. In this case, strict mode only applies when actually executing code that is - defined within a strict mode code unit.

- -

In order to conform to this specification, an ECMAScript implementation must implement both the full unrestricted - ECMAScript language and the strict mode variant of the ECMAScript language as defined by this specification. In addition, an - implementation must support the combination of unrestricted and strict mode code units - into a single composite program.

-
-
- -
-
-

4.3 Terms - and definitions

- -

For the purposes of this document, the following terms and definitions apply.

-
- -
-

4.3.1 type

- -

set of data values as defined in clause 6 of this specification

-
- -
-

4.3.2 - primitive value

- -

member of one of the types Undefined, Null, Boolean, Number, Symbol, or String as defined in clause 6

- -
-

NOTE A primitive value is a datum that is represented directly at the lowest level of the - language implementation.

-
-
- -
-

4.3.3 object

- -

member of the type Object

- -
-

NOTE An object is a collection of properties and has a single prototype object. The prototype - may be the null value.

-
-
- -
-

4.3.4 - constructor

- -

function object that creates and initializes objects

- -
-

NOTE The value of a constructor’s “prototype” property is a - prototype object that is used to implement inheritance and shared properties.

-
-
- -
-

4.3.5 prototype

- -

object that provides shared properties for other objects

- -
-

NOTE When a constructor creates an object, that object implicitly references the - constructor’s “prototype” property for the purpose of resolving property references. The - constructor’s “prototype” property can be referenced by the program expression - constructor.prototype, and properties added to an object’s prototype are shared, through - inheritance, by all objects sharing the prototype. Alternatively, a new object may be created with an explicitly specified - prototype by using the Object.create built-in function.

-
-
- -
-

4.3.6 - ordinary object

- -

object that has the default behaviour for the essential internal methods that must be supported by all objects.

-
- -
-

4.3.7 exotic - object

- -

object that has some alternative behaviour for one or more of the essential internal methods that must be supported by - all objects.

- -
-

NOTE Any object that is not an ordinary object is an exotic object.

-
-
- -
-

4.3.8 - standard object

- -

object whose semantics are defined by this specification.

-
- -
-

4.3.9 - built-in object

- -

object supplied by an ECMAScript implementation, independent of the host environment, that is present at the start of the - execution of an ECMAScript program

- -
-

NOTE Standard built-in objects are defined in this specification, and an ECMAScript - implementation may specify and define others. A built-in constructor is a built-in object that is also a - constructor.

-
-
- -
-

4.3.10 - undefined value

- -

primitive value used when a variable has not been assigned a value

-
- -
-

4.3.11 Undefined type

- -

type whose sole value is the undefined value

-
- -
-

4.3.12 null - value

- -

primitive value that represents the intentional absence of any object value

-
- -
-

4.3.13 Null type

- -

type whose sole value is the null value

-
- -
-

4.3.14 Boolean value

- -

member of the Boolean type

- -
-

NOTE There are only two Boolean values, true and false.

-
-
- -
-

4.3.15 Boolean type

- -

type consisting of the primitive values true and false

-
- -
-

4.3.16 - Boolean object

- -

member of the Object type that is an instance of the standard built-in Boolean constructor

- -
-

NOTE A Boolean object is created by using the Boolean constructor in a - new expression, supplying a Boolean value as an argument. The resulting object has an internal slot whose value is the Boolean value. A Boolean - object can be coerced to a Boolean value.

-
-
- -
-

4.3.17 String value

- -

primitive value that is a finite ordered sequence of zero or more 16-bit unsigned integer

- -
-

NOTE A String value is a member of the String type. Each integer value in the sequence usually - represents a single 16-bit unit of UTF-16 text. However, ECMAScript does not place any restrictions or requirements on the - values except that they must be 16-bit unsigned integers.

-
-
- -
-

4.3.18 String type

- -

set of all possible String values

-
- -
-

4.3.19 String - object

- -

member of the Object type that is an instance of the standard built-in String constructor

- -
-

NOTE A String object is created by using the String constructor in a - new expression, supplying a String value as an argument. The resulting object has an internal slot whose value is the String value. A String object - can be coerced to a String value by calling the String constructor as a function (21.1.1.1).

-
-
- -
-

4.3.20 Number value

- -

primitive value corresponding to a double-precision 64-bit binary format IEEE 754 value

- -
-

NOTE A Number value is a member of the Number type and is a direct representation of a - number.

-
-
- -
-

4.3.21 Number type

- -

set of all possible Number values including the special “Not-a-Number” (NaN) value, positive infinity, and - negative infinity

-
- -
-

4.3.22 Number - object

- -

member of the Object type that is an instance of the standard built-in Number constructor

- -
-

NOTE A Number object is created by using the Number constructor in a - new expression, supplying a Number value as an argument. The resulting object has an internal slot whose value is the Number value. A Number object - can be coerced to a Number value by calling the Number constructor as a function (20.1.1.1).

-
-
- -
-

4.3.23 Infinity

- -

number value that is the positive infinite Number value

-
- -
-

4.3.24 NaN

- -

number value that is an IEEE 754 “Not-a-Number” value

-
- -
-

4.3.25 Symbol - value

- -

primitive value that represents a unique, non-String Object property key.

-
- -
-

4.3.26 Symbol type

- -

set of all possible Symbol values

-
- -
-

4.3.27 Symbol - object

- -

member of the Object type that is an instance of the standard built-in Symbol constructor

-
- -
-

4.3.28 function

- -

member of the Object type that may be invoked as a subroutine

- -
-

NOTE In addition to its properties, a function contains executable code and state that - determine how it behaves when invoked. A function’s code may or may not be written in ECMAScript.

-
-
- -
-

4.3.29 - built-in function

- -

built-in object that is a function

- -
-

NOTE Examples of built-in functions include parseInt and Math.exp. An implementation may provide implementation-dependent built-in functions that - are not described in this specification.

-
-
- -
-

4.3.30 - property

- -

association between a key and a value that is a part of an object. The key be either a String value or a Symbol - value.

- -
-

NOTE Depending upon the form of the property the value may be represented either directly as a - data value (a primitive value, an object, or a function object) or indirectly by a pair of accessor functions.

-
-
- -
-

4.3.31 method

- -

function that is the value of a property

- -
-

NOTE When a function is called as a method of an object, the object is passed to the function - as its this value.

-
-
- -
-

4.3.32 - built-in method

- -

method that is a built-in function

- -
-

NOTE Standard built-in methods are defined in this specification, and an ECMAScript - implementation may specify and provide other additional built-in methods.

-
-
- -
-

4.3.33 - attribute

- -

internal value that defines some characteristic of a property

-
- -
-

4.3.34 own - property

- -

property that is directly contained by its object

-
- -
-

4.3.35 - inherited property

- -

property of an object that is not an own property but is a property (either own or inherited) of the object’s - prototype

-
-
- -
-

4.4 Organization of This Specification

- -

The remainder of this specification is organized as follows:

- -

Clause 5 defines the notational conventions used throughout the specification.

- -

Clauses 6−8.5.1 define the execution environment within which ECMAScript - programs operate.

- -

Clauses 10−16 define the actual ECMAScript programming language includings its syntactic encoding and the execution - semantics of all language features.

- -

Clauses 17−26 define the ECMAScript standard library. It includes the definitions of all of the standard objects that - are available for use by ECMAScript programs as they execute.

-
-
- -
-
-

5 Notational - Conventions

-
- -
-
-

5.1 Syntactic and Lexical Grammars

-
- -
-

5.1.1 - Context-Free Grammars

- -

A context-free grammar consists of a number of productions. Each production has an abstract symbol called a - nonterminal as its left-hand side, and a sequence of zero or more nonterminal and terminal symbols as - its right-hand side. For each grammar, the terminal symbols are drawn from a specified alphabet.

- -

A chain production is a production that has exactly one nonterminal symbol on its right-hand side along with zero - or more terminal symbols.

- -

Starting from a sentence consisting of a single distinguished nonterminal, called the goal symbol, a given - context-free grammar specifies a language, namely, the (perhaps infinite) set of possible sequences of terminal - symbols that can result from repeatedly replacing any nonterminal in the sequence with a right-hand side of a production for - which the nonterminal is the left-hand side.

-
- -
-

5.1.2 The Lexical and RegExp Grammars

- -

A lexical grammar for ECMAScript is given in clause 11. - This grammar has as its terminal symbols characters (Unicode code points) that conform to the rules for SourceCharacter defined in 10.1. It defines a set of productions, starting - from the goal symbol InputElementDiv or InputElementRegExp, that describe - how sequences of such characters are translated into a sequence of input elements.

- -

Input elements other than white space and comments form the terminal symbols for the syntactic grammar for ECMAScript and - are called ECMAScript tokens. These tokens are the reserved words, identifiers, literals, and punctuators of the - ECMAScript language. Moreover, line terminators, although not considered to be tokens, also become part of the stream of - input elements and guide the process of automatic semicolon insertion (11.9). Simple white space and single-line comments are discarded and do not - appear in the stream of input elements for the syntactic grammar. A MultiLineComment (that is, a - comment of the form “/*…*/” regardless of whether it spans more than one line) - is likewise simply discarded if it contains no line terminator; but if a MultiLineComment contains - one or more line terminators, then it is replaced by a single line terminator, which becomes part of the stream of input - elements for the syntactic grammar.

- -

A RegExp grammar for ECMAScript is given in 21.2.1. This grammar also has as its - terminal symbols the characters as defined by SourceCharacter. It defines a set of productions, - starting from the goal symbol Pattern, that describe how sequences of characters are translated into - regular expression patterns.

- -

Productions of the lexical and RegExp grammars are distinguished by having two colons “::” as - separating punctuation. The lexical and RegExp grammars share some productions.

-
- -
-

5.1.3 - The Numeric String Grammar

- -

Another grammar is used for translating Strings into numeric values. This grammar is similar to the part of the lexical - grammar having to do with numeric literals and has as its terminal symbols SourceCharacter. This - grammar appears in 7.1.3.1.

- -

Productions of the numeric string grammar are distinguished by having three colons “:::” as - punctuation.

-
- -
-

5.1.4 The - Syntactic Grammar

- -

The syntactic grammar for ECMAScript is given in clauses 11, 12, 13, 14, and 15. This grammar has ECMAScript - tokens defined by the lexical grammar as its terminal symbols (5.1.2). It - defines a set of productions, starting from the goal symbol Script, that describe how sequences of - tokens can form syntactically correct independent components of an ECMAScript programs.

- -

When a stream of characters is to be parsed as an ECMAScript script, it is first converted to a stream of input elements - by repeated application of the lexical grammar; this stream of input elements is then parsed by a single application of the - syntactic grammar. The script is syntactically in error if the tokens in the stream of input elements cannot be parsed as a - single instance of the goal nonterminal Script, with no tokens left over.

- -

Productions of the syntactic grammar are distinguished by having just one colon “:” as - punctuation.

- -

The syntactic grammar as presented in clauses 12, 13, 14 and 15 is actually not a complete account of which token - sequences are accepted as correct ECMAScript scripts. Certain additional token sequences are also accepted, namely, those - that would be described by the grammar if only semicolons were added to the sequence in certain places (such as before line - terminator characters). Furthermore, certain token sequences that are described by the grammar are not considered acceptable - if a terminator character appears in certain “awkward” places.

- -

In certain cases in order to avoid ambiguities the syntactic grammar uses generalized productions that permit token - sequences that are not valid ECMAScript scripts. For example, this technique is used for object literals and object - destructuring patterns. In such cases a more restrictive supplemental grammar is provided that further restricts the - acceptable token sequences. In certain contexts, when explicitly specific, the input elements corresponding to such a - production are parsed again using a goal symbol of a supplemental grammar. The script is syntactically in error if the - tokens in the stream of input elements cannot be parsed as a single instance of the supplemental goal symbol, with no tokens - left over.

-
- -
-

5.1.5 - Grammar Notation

- -

Terminal symbols of the lexical, RegExp, and numeric string grammars, and some of the terminal symbols of the other - grammars, are shown in fixed width font, both in the productions of the grammars and throughout this - specification whenever the text directly refers to such a terminal symbol. These are to appear in a script exactly as - written. All terminal symbol characters specified in this way are to be understood as the appropriate Unicode code points - from the Basic Latin range, as opposed to any similar-looking characters from other Unicode ranges.

- -

Nonterminal symbols are shown in italic type. The definition of a nonterminal (also called a - “production”) is introduced by the name of the nonterminal being defined followed by one or more colons. (The - number of colons indicates to which grammar the production belongs.) One or more alternative right-hand sides for the - nonterminal then follow on succeeding lines. For example, the syntactic definition:

- -
-
WhileStatement :
-
while ( Expression ) Statement
-
- -

states that the nonterminal WhileStatement represents the token while, followed by a - left parenthesis token, followed by an Expression, followed by a right parenthesis token, followed - by a Statement. The occurrences of Expression and Statement are themselves nonterminals. As another example, the syntactic definition:

- -
-
ArgumentList :
-
AssignmentExpression
-
ArgumentList , AssignmentExpression
-
- -

states that an ArgumentList may represent either a single AssignmentExpression or an ArgumentList, followed by a comma, followed by an AssignmentExpression. This definition of ArgumentList is recursive, that is, it is - defined in terms of itself. The result is that an ArgumentList may contain any positive number of - arguments, separated by commas, where each argument expression is an AssignmentExpression. Such - recursive definitions of nonterminals are common.

- -

The subscripted suffix “opt”, which may appear after a terminal or nonterminal, indicates an - optional symbol. The alternative containing the optional symbol actually specifies two right-hand sides, one that omits the - optional element and one that includes it. This means that:

- -
-
VariableDeclaration :
-
BindingIdentifier Initializeropt
-
- -

is a convenient abbreviation for:

- -
-
VariableDeclaration :
-
BindingIdentifier
-
BindingIdentifier Initializer
-
- -

and that:

- -
-
IterationStatement :
-
for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
-
- -

is a convenient abbreviation for:

- -
-
IterationStatement :
-
for ( LexicalDeclaration Expressionopt ) Statement
-
for ( LexicalDeclaration Expression ; Expressionopt ) Statement
-
- -

which in turn is an abbreviation for:

- -
-
IterationStatement :
-
for ( LexicalDeclaration ) Statement
-
for ( LexicalDeclaration Expression ) Statement
-
for ( LexicalDeclaration Expression ; ;) Statement
-
for ( LexicalDeclaration Expression ; Expression ) Statement
-
- -

so, in this example, the nonterminal IterationStatement actually has four alternative right-hand - sides.

- -

A production may be parameterized by a subscripted annotation of the form “[parameters]”, which - may appear as a suffix to the nonterminal symbol defined by the production. “parameters” may be - either a single name or a comma separated list of names. A parameterized production is shorthand for a set of productions - defining all combinations of the parameter names, preceeded by an underscore, appended to the parameterized nonterminal - symbol. This means that:

- -
-
StatementList[Return] :
-
ReturnStatement
-
ExpressionStatement
-
- -

is a convenient abbreviation for:

- -
-
StatementList :
-
ReturnStatement
-
ExpressionStatement
-
- -
-
StatementList_Return :
-
ReturnStatement
-
ExpressionStatement
-
- -

and that:

- -
-
StatementList[Return, In] :
-
ReturnStatement
-
ExpressionStatement
-
- -

is an abbreviation for:

- -
-
StatementList :
-
ReturnStatement
-
ExpressionStatement
-
- -
-
StatementList_Return :
-
ReturnStatement
-
ExpressionStatement
-
- -
-
StatementList_In :
-
ReturnStatement
-
ExpressionStatement
-
- -
-
StatementList_Return_In :
-
ReturnStatement
-
ExpressionStatement
-
- -

Multiple parameters produce a combinatory number of productions, not all of which are necessarily referenced in a - complete grammar.

- -

References to nonterminals on the right hand side of a production can also be parameterized. For example:

- -
-
StatementList :
-
ReturnStatement
-
ExpressionStatement[In]
-
- -

is equivalent to saying:

- -
-
StatementList :
-
ReturnStatement
-
ExpressionStatement_In
-
- -

A nonterminal reference may have both a parameter list and an “opt” suffix. For example:

- -
-
VariableDeclaration :
-
BindingIdentifier Initializer[In]opt
-
- -

is an abbreviation for:

- -
-
VariableDeclaration :
-
BindingIdentifier
-
BindingIdentifier Initializer_In
-
- -

Prefixing a parameter name with “?” on a right hand side nonterminal reference makes that - parameter value dependent upon the occurrence of the parameter name on the reference to the current production’s left - hand side symbol. For example:

- -
-
VariableDeclaration[In] :
-
BindingIdentifier Initializer[?In]
-
- -

is an abbreviation for:

- -
-
VariableDeclaration :
-
BindingIdentifier Initializer
-
- -
-
VariableDeclaration_In :
-
BindingIdentifier Initializer_In
-
- -

If a right hand side alternative is prefixed with “[+parameter]” that alternative is only available if the - named parameter was used in referencing the production’s nonterminal symbol. If a right hand side alternative is - prefixed with “[~parameter]” that alternative is only available if the named parameter was not used in - referencing the production’s nonterminal symbol. This means that:

- -
-
StatementList[Return] :
-
[+Return] ReturnStatement
-
ExpressionStatement
-
- -

is an abbreviation for:

- -
-
StatementList :
-
ExpressionStatement
-
- -
-
StatementList_Return :
-
ReturnStatement
-
ExpressionStatement
-
- -

and that

- -
-
StatementList[Return] :
-
[~Return] ReturnStatement
-
ExpressionStatement
-
- -

is an abbreviation for:

- -
-
StatementList :
-
ReturnStatement
-
ExpressionStatement
-
- -
-
StatementList_Return :
-
ExpressionStatement
-
- -

When the words “one of” follow the colon(s) in a grammar definition, they signify that each of the - terminal symbols on the following line or lines is an alternative definition. For example, the lexical grammar for - ECMAScript contains the production:

- -
-
NonZeroDigit :: one of
-
1 2 3 4 5 6 7 8 9
-
- -

which is merely a convenient abbreviation for:

- -
-
NonZeroDigit ::
-
1
-
2
-
3
-
4
-
5
-
6
-
7
-
8
-
9
-
- -

If the phrase “[empty]” appears as the right-hand side of a production, it indicates that the production's - right-hand side contains no terminals or nonterminals.

- -

If the phrase “[lookahead ∉ set]” appears in the right-hand side of a production, it - indicates that the production may not be used if the immediately following input token is a member of the given - set. The set can be written as a list of terminals enclosed in curly braces. For convenience, the set - can also be written as a nonterminal, in which case it represents the set of all terminals to which that nonterminal could - expand. If the set consists of a single terminal the pharse “[lookahead ≠ terminal]” by - be used.

- -

For example, given the definitions

- -
-
DecimalDigit :: one of
-
0 1 2 3 4 5 6 7 8 9
-
- -
-
DecimalDigits ::
-
DecimalDigit
-
DecimalDigits DecimalDigit
-
- -

the definition

- -
-
LookaheadExample ::
-
n [lookahead ∉ {1, 3, 5, 7, 9}] DecimalDigits
-
DecimalDigit [lookahead ∉ DecimalDigit]
-
- -

matches either the letter n followed by one or more decimal digits the first of which is even, or a decimal - digit not followed by another decimal digit.

- -

If the phrase “[no LineTerminator here]” appears in the right-hand side of a - production of the syntactic grammar, it indicates that the production is a restricted production: it may not be used - if a LineTerminator occurs in the input stream at the indicated position. For example, the - production:

- -
-
ThrowStatement :
-
throw [no LineTerminator here] Expression ;
-
- -

indicates that the production may not be used if a LineTerminator occurs in the script between - the throw token and the Expression.

- -

Unless the presence of a LineTerminator is forbidden by a restricted production, any number of - occurrences of LineTerminator may appear between any two consecutive tokens in the stream of input - elements without affecting the syntactic acceptability of the script.

- -

The lexical grammar has multiple goal symbols and the appropriate goal symbol to use depends upon the syntactic grammar - context. If a phrase of the form “[Lexical goal LexicalGoalSymbol]” appears on the - right-hand-side of a syntactic production then the next token must be lexically recognized using the indicated goal symbol. - In the absence of such a phrase the default lexical goal symbol is used.

- -

When an alternative in a production of the lexical grammar or the numeric string grammar appears to be a multi-character - token, it represents the sequence of characters that would make up such a token.

- -

The right-hand side of a production may specify that certain expansions are not permitted by using the phrase - “but not” and then indicating the expansions to be excluded. For example, the production:

- -
-
Identifier ::
-
IdentifierName but not ReservedWord
-
- -

means that the nonterminal Identifier may be replaced by any sequence of characters that could - replace IdentifierName provided that the same sequence of characters could not replace ReservedWord.

- -

Finally, a few nonterminal symbols are described by a descriptive phrase in sans-serif type in cases where it would be - impractical to list all the alternatives:

- -
-
SourceCharacter ::
-
any Unicode code point
-
-
-
- -
-

5.2 - Algorithm Conventions

- -

The specification often uses a numbered list to specify steps in an algorithm. These algorithms are used to precisely - specify the required semantics of ECMAScript language constructs. The algorithms are not intended to imply the use of any - specific implementation technique. In practice, there may be more efficient algorithms available to implement a given - feature.

- -

Algorithms may be explicitly parameterized, in which case the names and usage of the parameters must be provided as part of - the algorithm’s definition. In order to facilitate their use in multiple parts of this specification, some algorithms, - called abstract operations, are named and written in parameterized functional form so that they may be - referenced by name from within other algorithms.

- -

Algorithms may be associated with productions of one of the ECMAScript grammars. A production that has multiple - alternative definitions will typically have a distinct algorithm for each alternative. When an algorithm is associated with a - grammar production, it may reference the terminal and nonterminal symbols of the production alternative as if they were - parameters of the algorithm. When used in this manner, nonterminal symbols refer to the actual alternative definition that is - matched when parsing the script souce code.

- -

When an algorithm is associated with a production alternative, the alternative is typically shown without any “[ - ]” grammar annotations. Such annotations should only affect the syntactic recognition of the alternative and have no - effect on the associated semantics for the alternative.

- -

Unless explicitly specified otherwise, all chain productions have an implicit - associated definition for every algorithm that might be applied to that production’s left-hand side nonterminal. The - implicit definition simply reapplies the same algorithm name with the same parameters, if any, to the chain production’s sole right-hand side nonterminal and then result. For example, - assume there is a production:

- -
-
Block :
-
{ StatementList }
-
- -

but there is no corresponding Evaluation algorithm that is explicitly specified for that production. If in some algorithm - there is a statement of the form: “Return the result of evaluating - Block” it is implicit that an Evaluation algorithm exists of the form:

- -

Runtime Semantics: Evaluation

- -
Block : { StatementList }
-
    -
  1. Return the result of evaluating StatementList.
    2. -
- -

For clarity of expression, algorithm steps may be subdivided into sequential substeps. Substeps are indented and may - themselves be further divided into indented substeps. Outline numbering conventions are used to identify substeps with the - first level of substeps labelled with lower case alphabetic characters and the second level of substeps labelled with lower - case roman numerals. If more than three levels are required these rules repeat with the fourth level using numeric labels. For - example:

- -
    -
  1. Top-level step -
      -
    1. Substep.
      2. -
    2. Substep. -
        -
      1. Subsubstep. -
          -
        1. Subsubsubstep -
            -
          1. Subsubsubsubstep -
              -
            1. Subsubsubsubsubstep
              2. -
            -
            2. -
          -
          2. -
        -
        2. -
      -
      3. -
    -
    2. -
- -

A step or substep may be written as an “if” predicate that conditions its substeps. In this case, the substeps - are only applied if the predicate is true. If a step or substep begins with the word “else”, it is a predicate - that is the negation of the preceding “if” predicate step at the same level.

- -

A step may specify the iterative application of its substeps.

- -

A step may assert an invariant condition of its algorithm. Such assertions are used to make explicit algorithmic invariants - that would otherwise be implicit. Such assertions add no additional semantic requirements and hence need not be checked by an - implementation. They are used simply to clarify algorithms.

- -

Mathematical operations such as addition, subtraction, negation, multiplication, division, and the mathematical functions - defined later in this clause should always be understood as computing exact mathematical results on mathematical real numbers, - which do not include infinities and do not include a negative zero that is distinguished from positive zero. Algorithms in - this standard that model floating-point arithmetic include explicit steps, where necessary, to handle infinities and signed - zero and to perform rounding. If a mathematical operation or function is applied to a floating-point number, it should be - understood as being applied to the exact mathematical value represented by that floating-point number; such a floating-point - number must be finite, and if it is +0 or −0 then the - corresponding mathematical value is simply 0.

- -

The mathematical function abs(x) produces the absolute value of - x, which is −x if x is negative (less - than zero) and otherwise is x itself.

- -

The mathematical function sign(x) produces 1 if x is positive and −1 if x is negative. The sign function is not used in this standard for cases when x - is zero.

- -

The mathematical function min(x1, x2, ..., xn) produces the mathematically - smallest of x1 through xn.

- -

The notation “x modulo y” (y must be - finite and nonzero) computes a value k of the same sign as y (or zero) such that abs(k) < abs(y) and x−k = q × y for some integer q.

- -

The mathematical function floor(x) produces the largest integer - (closest to positive infinity) that is not larger than x.

- -
-

NOTE floor(x) = x−(x modulo 1).

-
-
- -
-

5.3 Static - Semantic Rules

- -

Context-free grammars are not sufficiently powerful to express all the rules that define whether a stream of input elements - form a valid ECMAScript script that may be evaluated. In some situations additional rules are needed that may be expressed - using either ECMAScript algorithm conventions or prose requirements. Such rules are always associated with a production of a - grammar and are called the static semantics of the production.

- -

Static Semantic Rules have names and typically are defined using an algorithm. Named Static Semantic Rules are associated - with grammar productions and a production that has multiple alternative definitions will typically have for each alternative a - distinct algorithm for each applicable named static semantic rule.

- -

Unless otherwise specified every grammar production alternative in this specification implicitly has a definition for a - static semantic rule named Contains which takes an argument named - symbol whose value is a terminal or nonterminal of the grammar that includes the associated production. The default - definition of Contains is:

- -
    -
  1. For each terminal and nonterminal grammar symbol, sym, in the definition of this production do -
      -
    1. If sym is the same grammar symbol as symbol, return true.
      2. -
    2. If sym is a nonterminal, then -
        -
      1. Let contained be the result of sym Contains symbol.
        2. -
      2. If contained is true, return true.
        3. -
      -
      3. -
    -
    2. -
  2. Return false.
    3. -
- -

The above definition is explicitly over-ridden for specific productions.

- -

A special kind of static semantic rule is an Early Error Rule. Early error rules define early error conditions (see clause 16) that are associated with specific grammar productions. - Evaluation of most early error rules are not explicitly invoked within the algorithms of this specification. A conforming - implementation must, prior to the first evaluation of a Script, validate all of the early error rules - of the productions used to parse that Script. If any of the early error rules are violated the Script is invalid and cannot be evaluated.

-
-
- -
-
-

6 - ECMAScript Data Types and Values

- -

Algorithms within this specification manipulate values each of which has an associated type. The possible value types are - exactly those defined in this clause. Types are further subclassified into ECMAScript language types and specification - types.

- -

Within this specification, the notation “Type(x)” is - used as shorthand for “the type of x” where “type” refers to the ECMAScript language and specification types defined in - this clause.

-
- -
-
-

6.1 - ECMAScript Language Types

- -

An ECMAScript language type corresponds to values that are directly manipulated by an ECMAScript programmer using the - ECMAScript language. The ECMAScript language types are Undefined, Null, Boolean, String, Symbol, Number, and Object. An - ECMAScript language value is a value that is characterized by an ECMAScript language type.

-
- -
-

6.1.1 The Undefined Type

- -

The Undefined type has exactly one value, called undefined. Any variable that has not been assigned a value has - the value undefined.

-
- -
-

6.1.2 The Null Type

- -

The Null type has exactly one value, called null.

-
- -
-

6.1.3 The Boolean Type

- -

The Boolean type represents a logical entity having two values, called true and false.

-
- -
-

6.1.4 The String Type

- -

The String type is the set of all finite ordered sequences of zero or more 16-bit unsigned integer values - (“elements”). The String type is generally used to represent textual data in a running ECMAScript program, in - which case each element in the String is treated as a UTF-16 code unit value. Each element is regarded as occupying a - position within the sequence. These positions are indexed with nonnegative integers. The first element (if any) is at index - 0, the next element (if any) at index 1, and so on. The length of a String is the number of elements (i.e., 16-bit values) - within it. The empty String has length zero and therefore contains no elements.

- -

Where ECMAScript operations interpret String values, each element is interpreted as a single UTF-16 code unit. However, - ECMAScript does not place any restrictions or requirements on the sequence of code units in a String value, so they may be - ill-formed when interpreted as UTF-16 code unit sequences. Operations that do not interpret String contents treat them as - sequences of undifferentiated 16-bit unsigned integers. No operations ensure that Strings are in a normalized form. Only - operations that are explicitly specified to be language or locale sensitive produce language-sensitive results

- -
-

NOTE The rationale behind this design was to keep the implementation of Strings as simple and - high-performing as possible. If ECMAScript source code is in Normalized Form C, string literals are guaranteed to also be - normalized, as long as they do not contain any Unicode escape sequences.

-
- -

Some operations interpret String contents as UTF-16 encoded Unicode code points. In that case the interpretation is:

- -
    -
  • -

    A code unit in the range 0 to 0xD7FF or in the range 0xE000 to 0xFFFF is interpreted as a code point with the same value.

    -
    • - -
  • -

    A sequence of two code units, where the first code unit c1 is in the range 0xD800 to 0xDBFF and the second code unit - c2 is in the range 0xDC00 to 0xDFFF, is a surrogate pair and is interpreted as a code point with the value (c1 - - 0xD800) × 0x400 + (c2 – 0xDC00) + 0x10000.

    -
    • - -
  • -

    A code unit that is in the range 0xD800 to 0xDFFF, but is not part of a surrogate pair, is interpreted as a code point - with the same value.

    -
    • -
-
- -
-
-

6.1.5 The Symbol Type

- -

The Symbol type is the set of all non-String values that may be used as the key of an Object property (6.1.7).

- -

Each possible Symbol values is unique and immutable.

- -

Each Symbol value immutably holds an associated value called [[Description]] that is either undefined or a String value.

-
- -
-

6.1.5.1 Well-Known Symbols

- -

Well-known symbols are built-in Symbol values that are explicitly referenced by algorithms of this specification. They - are typically used as the keys of properties whose values serve as extension points of a specification algorithm. Unless - otherwise specified, well-known symbols values are shared by all Code Realms (8.1.2.5).

- -

Within this specification a well-known symbol is referred to by using a notation of the form @@name, where - “name” is one of the values listed in Table 1.

- -
-
Table 1— Well-known Symbols
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Specification Name[[Description]]Value and Purpose
@@create"Symbol.create"A method used to allocate an object. Called from the [[Construct]] internal method.
@@hasInstance"Symbol.hasInstance"A method that determines if a constructor object recognizes an object as one of the constructor’s instances. Called by the semantics of the instanceof operator.
@@isConcatSpreadable"Symbol.isConcatSpreadable"A Boolean value that if true indicates that an object should be flatten to its array elements by Array.prototype.concat.
@@isRegExp"Symbol.isRegExp"A Boolean value that if true indicates that an object may be used as a regular expression.
@@iterator"Symbol.iterator"A method that returns the default iterator for an object. Called by the semantics of the for-of statement.
@@toPrimitive"Symbol.toPrimitive"A method that converts an object to a corresponding primitive value. Called by the ToPrimitive abstract operation.
@@toStringTag"Symbol.toStringTag"A string value that is used in the creation of the default string description of an object. Called by the built-in method Object.prototype.toString.
@@unscopables"Symbol.unscopables"An Array of string values that are property names that are excluded from the with environment bindings of the associated objects.
-
-
-
- -
-

6.1.6 The Number Type

- -

The Number type has exactly 18437736874454810627 (that is, 264−253+3) values, representing the double-precision - 64-bit format IEEE 754 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic, except that the 9007199254740990 (that is, 253−2) distinct “Not-a-Number” values of the IEEE Standard are represented in - ECMAScript as a single special NaN value. (Note that the NaN value is produced by the program expression - NaN.) In some implementations, external code might be able to detect a difference between various Not-a-Number - values, but such behaviour is implementation-dependent; to ECMAScript code, all NaN values are indistinguishable from each - other.

- -

There are two other special values, called positive Infinity and negative Infinity. For brevity, these - values are also referred to for expository purposes by the symbols +∞ and −∞, respectively. (Note that these two infinite Number values are produced by the program - expressions +Infinity (or simply Infinity) and -Infinity.)

- -

The other 18437736874454810624 (that is, 264−253) values are called the finite numbers. Half of these are - positive numbers and half are negative numbers; for every finite positive Number value there is a corresponding negative - value having the same magnitude.

- -

Note that there is both a positive zero and a negative zero. For brevity, these values are also referred to - for expository purposes by the symbols +0 and −0, respectively. - (Note that these two different zero Number values are produced by the program expressions +0 (or simply - 0) and -0.)

- -

The 18437736874454810622 (that is, 264−253−2) finite nonzero values are of two kinds:

- -

18428729675200069632 (that is, 264−254) of them are normalized, having the form

- -
s × m × 2e
- -

where s is +1 or −1, m is a positive integer less than 253 but not less than 252, and - e is an integer ranging from −1074 to 971, inclusive.

- -

The remaining 9007199254740990 (that is, 253−2) values are denormalized, having the form

- -
s × m × 2e
- -

where s is +1 or −1, m is a positive integer less than 252, and e is −1074.

- -

Note that all the positive and negative integers whose magnitude is no greater than 253 are representable in the Number type (indeed, the integer 0 has two representations, +0 and -0).

- -

A finite number has an odd significand if it is nonzero and the integer m used to express it (in one of - the two forms shown above) is odd. Otherwise, it has an even significand.

- -

In this specification, the phrase “the Number value for - x” where x represents an exact nonzero real mathematical quantity (which might even be an - irrational number such as π) means a Number value chosen in the - following manner. Consider the set of all finite values of the Number type, with −0 removed - and with two additional values added to it that are not representable in the Number type, namely 21024 (which is +1 × - 253 × 2971) and −21024 (which is −1 × 253 × 2971). - Choose the member of this set that is closest in value to x. If two values of the set are equally close, then the - one with an even significand is chosen; for this purpose, the two extra values 21024 and −21024 are considered - to have even significands. Finally, if 21024 was chosen, - replace it with +∞; if −21024 was chosen, replace it with −∞; if +0 was chosen, replace it with −0 if and only if x is less - than zero; any other chosen value is used unchanged. The result is the Number value for x. (This procedure - corresponds exactly to the behaviour of the IEEE 754 “round to nearest” mode.)

- -

Some ECMAScript operators deal only with integers in the range −231 through 231−1, - inclusive, or in the range 0 through 232−1, inclusive. These operators accept any value of the Number type but first convert each - such value to one of 232 integer values. See the descriptions - of the ToInt32 and ToUint32 operators in 7.1.5 and 7.1.6, respectively.

-
- -
-
-

6.1.7 The - Object Type

- -

An Object is logically a collection of properties. Each property is either a data property, or an accessor - property:

- -
    -
  • -

    A data property associates a key value with an ECMAScript language - value and a set of Boolean attributes.

    -
    • - -
  • -

    An accessor property associates a key value with one or two accessor functions, and a set of Boolean - attributes. The accessor functions are used to store or retrieve an ECMAScript language value that is associated with the property.

    -
    • -
- -

Properties are identified using key values. A key value is either an ECMAScript String value or a Symbol value. All - String and Symbol values, including the empty string, are valid as property keys.

- -

An integer index is a String-valued property key that is a canonical numeric String (see 7.1.16) and whose numeric value is either +0 or a positive integer. An array index is an integer index whose numeric value i is - in the range 0 ≤ i < 232−1 and i ≠ −0.

- -

Property keys are used to access properties and their values. There are two kinds of access for properties: get - and set, corresponding to value retrieval and assignment, respectively. The properties accessible via get and set - access includes both own properties that are a direct part of an object and inherited properties which are - provided by another associated object via a property inheritance relationship. Inherited properties may be either own or - inherited properties of the associated object. Each own properties of an object must each have a key value that is - distinct from the key values of the other own properties of that object.

- -

All objects are logically collections of properties, but there are multiple forms of objects that differ in their - semantics for accessing and manipulating their properties. Ordinary objects are the most common form of objects - and have the default object semantics. An exotic object is any form of object whose property semantics differ in - any way from the default semantics.

-
- -
-

6.1.7.1 Property Attributes

- -

Attributes are used in this specification to define and explain the state of Object properties. A data property - associates a key value with the attributes listed in Table 2.

- -
-
Table 2 — Attributes of a Data Property
- - - - - - - - - - - - - - - - - - - - - - - - - - -
Attribute NameValue DomainDescription
[[Value]]Any ECMAScript language typeThe value retrieved by a get access of the property.
[[Writable]]BooleanIf false, attempts by ECMAScript code to change the property’s [[Value]] attribute using [[Set]] will not succeed.
[[Enumerable]]BooleanIf true, the property will be enumerated by a for-in enumeration (see 13.6.3.5). Otherwise, the property is said to be non-enumerable.
[[Configurable]]BooleanIf false, attempts to delete the property, change the property to be an accessor property, or change its attributes (other than [[Value]], or changing [[Writable]] to false) will fail.
-
- -

An accessor property associates a key value with the attributes listed in Table 3.

- -
-
Table 3 — Attributes of an Accessor Property
- - - - - - - - - - - - - - - - - - - - - - - - - - -
Attribute NameValue DomainDescription
[[Get]]Object or UndefinedIf the value is an Object it must be a function Object. The function’s [[Call]] internal method (Table 6) is called with an empty arguments list to retrieve the property value each time a get access of the property is performed.
[[Set]]Object or UndefinedIf the value is an Object it must be a function Object. The function’s [[Call]] internal method (Table 6) is called with an arguments list containing the assigned value as its sole argument each time a set access of the property is performed. The effect of a property's [[Set]] internal method may, but is not required to, have an effect on the value returned by subsequent calls to the property's [[Get]] internal method.
[[Enumerable]]BooleanIf true, the property is to be enumerated by a for-in enumeration (see 13.6.3.5). Otherwise, the property is said to be non-enumerable.
[[Configurable]]BooleanIf false, attempts to delete the property, change the property to be a data property, or change its attributes will fail.
-
- -

If the initial values of a property’s attributes are not explicitly specified by this specification, the default - value defined in Table 4 is used.

- -
-
Table 4 — Default Attribute Values
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Attribute NameDefault Value
[[Value]]undefined
[[Get]]undefined
[[Set]]undefined
[[Writable]]false
[[Enumerable]]false
[[Configurable]]false
-
-
- -
-

6.1.7.2 Object Internal Methods and Internal Slots

- -

The actual semantics of objects, in ECMAScript, are specified via algorithms called internal methods. Each - object in an ECMAScript engine is associated with a set of internal methods that defines its runtime behaviour. These - internal methods are not part of the ECMAScript language. They are defined by this specification purely for expository - purposes. However, each object within an implementation of ECMAScript must behave as specified by the internal methods - associated with it. The exact manner in which this is accomplished is determined by the implementation.

- -

Internal method names are polymorphic. This means that different object values may perform different algorithms when a - common internal method name is invoked upon them. If, at runtime, the implementation of an algorithm attempts to use an - internal method of an object that the object does not support, a TypeError exception is thrown.

- -

Internal slots correspond to internal state that is associated with objects and used by various ECMAScript - specification algorithms. Internal slots are not object properties and they are not inherited. Depending upon the specific - internal slot specification, such state may consist of values of any ECMAScript - language type or of specific ECMA specification type values. Unless explicitly specified otherwise, internal slots are - allocated as part of the process of creating an object and may not be dynamically added to an object. Unless specified - otherwise, the initial value of an internal slot is the value undefined. Various algorithms - within this specification create objects that have internal slots. However, the ECMAScript language provides no direct way - to associate internal slots with an object.

- -

Internal methods and internal slots are identified within this specification using names enclosed in double square - brackets [[ ]].

- -

Table 5 summarizes the essential internal methods used by this specification that are - applicable to all objects created or manipulated by ECMAScript code. Every object must have algorithms for all of the - essential internal methods. However, all objects do not necessarily use the same algorithms for those methods.

- -

The “Signature” column of Table 5 and other similar tables describes the invocation - pattern for each internal method. The invocation pattern always includes a parenthesized list of descriptive parameter - names. If a parameter name is the same as an ECMAScript type name then the name describes the required type of the - parameter value. If an internal method explicitly returns a value, its parameter list is followed by the symbol - “→” and the type name of the returned value. The type names used in signatures refer to the types defined - in clause 6 augmented by the following additional names. - “any” means the value may be any ECMAScript language type. - An internal method implicitly returns a Completion Record as - described in 6.2.2. In addition to its parameters, an internal - method always has access to the object upon which it is invoked as a method.

- -
-
Table 5 — Essential Internal Methods
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Internal MethodSignatureDescription
[[GetPrototypeOf]]()→Object or NullDetermine the object that provides inherited properties for this object. A null value indicates that there are no inherited properties.
[[SetPrototypeOf]](Object or Null)→BooleanAssociate with an object another object that provides inherited properties. Passing null indicates that there are no inherited properties. Returns true indicating that the operation was completed successfully or false indicating that the operation was not successful.
[[IsExtensible]]( )→BooleanDetermine whether it is permitted to add additional properties to an object.
[[PreventExtensions]]( )→BooleanControl whether new properties may be added to an object. Returns true indicating that the operation was completed successfully or false indicating that the operation was not successful.
[[GetOwnProperty]] -

(propertyKey) →

- -

Undefined or Property Descriptor

- 		Returns a Property Descriptor for the own property of this object whose key is propertyKey, or undefined if no such property exists.
[[HasProperty]](propertyKey) → BooleanReturns a Boolean value indicating whether the object already has either an own or inherited property whose key is propertyKey.
[[Get]](propertyKey, Receiver) → anyRetrieve the value of an object’s property using the propertyKey parameter. If any ECMAScript code must be executed to retrieve the property value, Receiver is used as the this value when evaluating the code.
[[Set]](propertyKey,value, Receiver) → BooleanTry to set the value of an object’s property indentified by propertyKey to value. If any ECMAScript code must be executed to set the property value, Receiver is used as the this value when evaluating the code. Returns true indicating that the property value was set or false indicating that it could not be set.
[[Delete]](propertyKey) → BooleanRemoves the own property indentified by the propertyKey parameter from the object. Return false if the property was not deleted and is still present. Return true if the property was deleted or was not present.
[[DefineOwnProperty]](propertyKey, PropertyDescriptor) → BooleanCreates or alters the named own property to have the state described by a Property Descriptor. Returns true indicating that the property was successfully created/updated or false indicating that the property could not be created or updated.
[[Enumerate]]()→ObjectReturns an iterator object over the string values of the keys of the enumerable properties of the object.
[[OwnPropertyKeys]]()→Array of propertyKeyReturns an Array object whose elements are all of the own property keys for the object.
-
- -

Table 6 summarizes additional essential internal methods that are supported by objects that may - be called as functions.

- -
-
Table 6 — Additional Essential Internal Methods of Function Objects
- - - - - - - - - - - - - - - - -
Internal MethodSignatureDescription
[[Call]](any, a List of any) → anyExecutes code associated with the object. Invoked via a function call expression. The arguments to the internal method are a this value and a list containing the arguments passed to the function by a call expression. Objects that implement this internal method are callable.
[[Construct]](a List of any) → ObjectCreates an object. Invoked via the new operator. The arguments to the internal method are the arguments passed to the new operator. Objects that implement this internal method are called constructors. A Function object is not necessarily a constructor and such non-constructor Function objects do not have a [[Construct]] internal method.
-
- -

The semantics of the essential internal method for ordinary objects and standard exotic objects are specified in clause 8.5.1. If any specified use of an exotic object's internal methods is not - supported by an implementation, that usage must throw a TypeError exception when attempted.

-
- -
-

6.1.7.3 Invariants of the Essential Internal Methods

- -

The Internal Methods of Objects of an ECMAScript engine must conform to the list of invariants specified below. - Ordinary ECMAScript Objects as well as all standard exotic objects in this specification maintain these invariants. - ECMAScript Proxy objects maintain these invariants by means of runtime checks on the result of traps invoked on the - [[ProxyHandler]] object.

- -

Any implementation provided exotic objects must also maintain these invariants for those objects. Violation of these - invariants may cause ECMAScript code to have unpredictable behaviour and create security issues. However, violation of - these invariants must never compromise the memory safety of an implementation.

- -

Definitions:

- -

● The target of an internal method is the object the internal method is called upon.

- -

● A target is non-extensible if it has been observed to return false from its [[IsExtensible]] - internal method, or true from its [[PreventExtensions]] internal method.

- -

● A non-existent property is a property that does not exist as an own property on a non-extensible - target.

- -

● All references to SameValue are according to the definition of SameValue algorithm specified in 7.2.3.

- -

[[GetPrototypeOf]] ( )

- -

● The Type of the return value must be either Object or Null.

- -

● If target is non-extensible, and [[GetPrototypeOf]] returns a value v, then any future calls to - [[GetPrototypeOf]] should return the SameValue as v.

- -

● An object’s prototype chain must have finite length (that is, starting from any object, recursively - applying the [[GetPrototypeOf]] internal method to its result must eventually lead to the value null.

- -

[[SetPrototypeOf]] (V)

- -

● The Type of the return value must be Boolean.

- -

● If target is non-extensible, [[SetPrototypeOf]] must return false, unless V is the SameValue as the target’s observed [[GetPrototypeOf]] value.

- -

[[PreventExtensions]] ( )

- -

● The Type of the return value must be Boolean.

- -

● If [[PreventExtensions]] returns true, all future calls to [[IsExtensible]] on the target must return - false and the target is now considered non-extensible.

- -

[[GetOwnProperty]] (P)

- -

● The Type of the return value must be either Object or Undefined.

- -

● If the Type of the return value is Object, that object must be a complete property descriptor (see 6.2.4.6).

- -

● If a property is described as a data property and it may return different values over time, then either - or both of the Desc.[[Writable]] and Desc.[[Configurable]] attributes must be true even if no mechanism to change the - value is exposed via the other internal methods.

- -

● If a property P is described as a data property with Desc.[[Value]] equal to v and Desc.[[Writable]] and - Desc.[[Configurable]] are both false, then the SameValue must be returned for the - Desc.[[Value]] attribute of the property on all future calls to [[GetOwnProperty]] ( P ).

- -

● If P’s attributes other than [[Writable]] may change over time or if the property might disappear, - then P’s [[Configurable]] attribute must be true.

- -

● If the [[Writable]] attribute may change from false to true, then the [[Configurable]] attribute must be - true.

- -

● If the target is non-extensible and P is non-existent, then all future calls to [[GetOwnProperty]] (P) - on the target must describe P as non-existent (i.e. [[GetOwnProperty]] (P) must return undefined)

- -

[[DefineOwnProperty]] (P, Desc)

- -

● The Type of the return value must be Boolean.

- -

● [[DefineOwnProperty]] must return false if P has previously been observed as a non-configurable own - property of the target, unless either:

- -

1. P is a non-configurable writable own data property. A non-configurable writable data property can be changed - into a non-configurable non-writable data property.

- -

2. All attributes in Desc are the SameValue as P’s attributes.

- -

● [[DefineOwnProperty]] (P, Desc) must return false if target is non-extensible and P is a non-existent own - property. That is, a non-extensible target object cannot be extended with new properties.

- -

[[HasProperty]] ( P )

- -

● The Type of the return value must be Boolean.

- -

● If P was previously observed as a non-configurable data or accessor own property of the target, - [[HasProperty]] must return true.

- -

[[Get]] (P, Receiver)

- -

● If P was previously observed as a non-configurable, non-writable own data property of the target with - value v, then [[Get]] must return the SameValue.

- -

● If P was previously observed as a non-configurable own accessor property of the target whose [[Get]] - attribute is undefined, the [[Get]] operation must return undefined.

- -

[[Set]] ( P, V, Receiver)

- -

● The Type of the return value must be Boolean.

- -

● If P was previously observed as a non-configurable, non-writable own data property of the target, then - [[Set]] must return false unless V is the SameValue as P’s [[Value]] attribute.

- -

● If P was previously observed as a non-configurable own accessor property of the target whose [[Set]] - attribute is undefined, the [[Set]] operation must return false.

- -

[[Delete]] ( P )

- -

● The Type of the return value must be Boolean.

- -

● If P was previously observed to be a non-configurable own data or accessor property of the target, - [[Delete]] must return false.

- -

[[Enumerate]] ( )

- -

● The Type of the return value must be Object.

- -

[[OwnPropertyKeys]] ( )

- -

● The Type of the return value must be Object.

- -

● The return value must be an exotic Array object.

- -

● The returned array must contain at least the string and symbol-valued names of all own properties of the - target that have previously been observed as non-configurable.

- -

● If the target is non-extensible, it may not claim to have any own properties not observed by - [[OwnPropertyNames]].

- -

[[Construct]] ( )

- -

● The Type of the return value must be Object.

-
- -
-

6.1.7.4 Well-Known Intrinsic Objects

- -

Well-known intrinsics are built-in objects that are explicitly referenced by the algorithms of this specification and - which usually have Realm specific identities. Unless otherwise specified each intrinsic - object actually corresponds to a set of similar objects, one per Realm.

- -

Within this specification a reference such as %name% means the intrinsic object, associated with the current Realm, corresponding to the name. Determination of the current Realm and its intrinsics is described in 8.1.2.5. The well-known intrinsics are listed in Table 7.

- -
-
Table 7 — Well-known Intrinsic Objects
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Intrinsic NameGlobal NameECMAScript Language Association
%ObjectPrototype%The initial value of the "prototype" data property of the intrinsic %Object%. (19.1.3)
%ThrowTypeError%A function that, when called, throws a TypeError exception.
%FunctionPrototype%The initial value of the "prototype" data property of the intrinsic %Function%.
%Object%"Object"The Object constructor (19.1.1)
%ObjProto_toString%The initial value of the "toString" data property of the intrinsic %ObjectPrototype%. (19.1.3.6)
%Function%"Function"The Function constructor (19.2.1)
%Array%"Array"The Array constructor (22.1.1)
%ArrayPrototype%The initial value of the "prototype" data property of the intrinsic %Array%.
%ArrayProto_values%The initial value of the "values" data property of the intrinsic %ArrayPrototype%. (22.1.3.29)
%ArrayIteratorPrototype%The prototype object used for
Iterator objects created by the CreateArrayIterator abstract operation.
%String%"String"The String constructor (21.1.1)
%StringPrototype%The initial value of the "prototype" data property of the intrinsic %String%.
%StringIteratorPrototype%The prototype object used for
Iterator objects created by the CreateStringIterator abstract operation
%Boolean%"Boolean"The initial value of the global object property named "Boolean".
%BooleanPrototype%The initial value of the "prototype" data property of the intrinsic %Boolean%.
%Number%"Number"The initial value of the global object property named "Number".
%NumberPrototype%The initial value of the "prototype" data property of the intrinsic %Number%.
%Date%"Date"The initial value of the global object property named "Date".
%DatePrototype%The initial value of the "prototype" data property of the intrinsic %Date%.
%RegExp%"RegExp"The initial value of the global object property named "RegExp".
%RegExpPrototype%The initial value of the "prototype" data property of the intrinsic %RegExp%.
%Map%"Map"The initial value of the global object property named "Map".
%MapPrototype%The initial value of the "prototype" data property of the intrinsic %Map%.
%MapIteratorPrototype%The prototype object used for
Iterator objects created by the CreateMapIterator abstract operation
%WeakMap%"WeakMap"The initial value of the global object property named "WeakMap".
%WeakMapPrototype%The initial value of the "prototype" data property of the intrinsic %WeakMap%.
%Set%"Set"The initial value of the global object property named "Set".
%SetPrototype%The initial value of the "prototype" data property of the intrinsic %Set%.
%WeakSet%"WeakSet"The initial value of the global object property named "WeakSet".
%WeakSetPrototype%The initial value of the "prototype" data property of the intrinsic %WeakSet%.
%SetIteratorPrototype%The prototype object used for
Iterator objects created by the CreateSetIterator abstract operation
%GeneratorFunction%The constructor of generator functions.
%Generator%The initial value of the prototype property of the %GeneratorFunction intrinsic
%GeneratorPrototype%The initial value of the prototype property of the %Generator% intrinsic
%Error%
%EvalError%
%RangeError%
%ReferenceError%
%SyntaxError%
%TypeError%
%URIError%
%ErrorPrototype%
%EvalErrorPrototype%
%RangeErrorPrototype%
%ReferenceErrorPrototype%
%SyntaxErrorPrototype%
%TypeErrorPrototype%
%URIErrorPrototype%
%ArrayBuffer%
%ArrayBufferPrototype%The initial value of the "prototype" data property of the intrinsic %ArrayBuffer%.
%TypedArray%
%TypedArrayPrototype%The initial value of the "prototype" data property of the intrinsic %TypedArray%.
%Int8Array%
%Int8ArrayPrototype%
%DataView%
%DataViewPrototype%
%ThrowTypeError%A function object that unconditionally throws a new instance of %TypeError%.
%Realm%
%RealmPrototype%
%Promise%
%PromisePrototype%
%Loader%
%LoaderPrototype%
%LoaderIteratorPrototype%
%ReturnUndefined%
%Symbol%
-
-
-
-
- -
-
-

6.2 ECMAScript Specification Types

- -

A specification type corresponds to meta-values that are used within algorithms to describe the semantics of ECMAScript - language constructs and ECMAScript language types. The specification types are Reference, List, Completion, Property Descriptor, Lexical - Environment, Environment Record, and Data Block. - Specification type values are specification artefacts that do not necessarily correspond to any specific entity within an - ECMAScript implementation. Specification type values may be used to describe intermediate results of ECMAScript expression - evaluation but such values cannot be stored as properties of objects or values of ECMAScript language variables.

-
- -
-

6.2.1 The List and Record Specification Type

- -

The List type is used to explain the evaluation of argument lists (see 12.3.6) in - new expressions, in function calls, and in other algorithms where a simple ordered list of values is needed. - Values of the List type are simply ordered sequences of list elements containing the individual values. These sequences may - be of any length. The elements of a list may be randomly accessed using 0-origin indices. For notational convience an - array-like syntax can be used to access List elements. For example, arguments[2] is shorthand for saying the - 3rd element of the List arguments.

- -

The Record type is used to describe data aggregations within the algorithms of this specification. A Record type value - consists of one or more named fields. The value of each field is either an ECMAScript value or an abstract value - represented by a name associated with the Record type. Field names are always enclosed in double brackets, for example - [[value]]

- -

For notational convenience within this specification, an object literal-like syntax can be used to express a Record - value. For example, {[[field1]]: 42, [[field2]]: false, [[field3]]: empty} defines a Record value that has - three fields each of which is initialized to a specific value. Field name order is not significant. Any fields that are not - explicitly listed are considered to be absent.

- -

In specification text and algorithms, dot notation may be used to refer to a specific field of a Record value. For - example, if R is the record shown in the previous paragraph then R.[[field2]] is shorthand for “the field of R named - [[field2]]”.

- -

Schema for commonly used Record field combinations may be named, and that name may be used as a prefix to a literal - Record value to identify the specific kind of aggregations that is being described. For example: - PropertyDescriptor{[[Value]]: 42, [[Writable]]: false, [[Configurable]]: true}.

-
- -
-
-

6.2.2 The Completion Record Specification Type

- -

The Completion type is a Record used to explain the runtime propagation of values and control flow such as the - behaviour of statements (break, continue, return and throw) that - perform nonlocal transfers of control.

- -

Values of the Completion type are Record values whole fields are defined as by Table 8.

- -
-
Table 8 — Completion Record Fields
- - - - - - - - - - - - - - - - - - - - - -
Field NameValueMeaning
[[type]]One of normal, break, continue, return, or throwThe type of completion that occurred.
[[value]]any ECMAScript language value or emptyThe value that was produced.
[[target]]any ECMAScript string or emptyThe target label for directed control transfers.
-
- -

The term “abrupt completion” refers to any completion with a [[type]] value other than normal.

-
- -
-

6.2.2.1 - NormalCompletion

- -

The abstract operation NormalCompletion with a single argument, such as:

- -
    -
  1. Return NormalCompletion(argument).
    2. -
- -

Is a shorthand that is defined as follows:

- -
    -
  1. Return Completion{[[type]]: normal, [[value]]: argument, [[target]]:empty}.
    2. -
-
- -
-

6.2.2.2 Implicit Completion Values

- -

The algorithms of this specification often implicitly return Completion Records whose [[type]] is normal. Unless it is - otherwise obvious from the context, an algorithm statement that returns a value that is not a Completion Record, such as:

- -
    -
  1. Return "Infinity".
    2. -
- -

Generally means the same thing as:

- -
    -
  1. Return NormalCompletion("Infinity").
    2. -
- -

A “return” statement without a value in an algorithm step - means the same thing as:

- -
    -
  1. Return NormalCompletion(undefined).
    2. -
- -

Similarly, any reference to a Completion Record value that is - in a context that does not explicitly require a complete Completion - Record value is equivalent to an explicit reference to the [[value]] field of the Completion Record value unless the Completion Record is an abrupt completion.

-
- -
-

6.2.2.3 Throw an Exception

- -

Algorithms steps that say to throw an exception, such as

- -
    -
  1. Throw a TypeError exception.
    2. -
- -

mean the same things as:

- -
    -
  1. Return Completion{[[type]]: throw, [[value]]: a newly created TypeError object, [[target]]:empty}.
    2. -
-
- -
-

6.2.2.4 - ReturnIfAbrupt

- -

Algorithms steps that say

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
- -

mean the same thing as:

- -
    -
  1. If argument is an abrupt completion, then return - argument.
    2. -
  2. Else if argument is a Completion Record, then let - argument be argument.[[value]].
    3. -
-
-
- -
-
-

6.2.3 The Reference Specification Type

- -
-

NOTE The Reference type is used to explain the behaviour of such operators as - delete, typeof, the assignment operators, the super keyword and other language - features. For example, the left-hand operand of an assignment is expected to produce a reference.

-
- -

A Reference is a resolved name or property binding. A Reference consists of three components, the - base value, the referenced name and the Boolean valued strict reference flag. The - base value is either undefined, an Object, a Boolean, a String, a Symbol, a Number, or an environment - record (8.1.1). A base value of undefined indicates that the - Reference could not be resolved to a binding. The referenced name is a String or Symbol value.

- -

A Super Reference is a Reference that is used to represents a name binding that was expressed using the super keyword. - A Super Reference has an additional thisValue component and its base value will never be an - environment record.

- -

The following abstract operations are used in this specification to access the components of references:

- -
    -
  • -

    GetBase(V). Returns the base value component of the reference V.

    -
    • - -
  • -

    GetReferencedName(V). Returns the referenced name component of the reference V.

    -
    • - -
  • -

    IsStrictReference(V). Returns the strict reference flag component of the reference V.

    -
    • - -
  • -

    HasPrimitiveBase(V). Returns true if Type(base) - is a Boolean, String, Symbol, or Number.

    -
    • - -
  • -

    IsPropertyReference(V). Returns true if either the base value is an object or HasPrimitiveBase(V) is - true; otherwise returns false.

    -
    • - -
  • -

    IsUnresolvableReference(V). Returns true if the base value is undefined and false - otherwise.

    -
    • - -
  • -

    IsSuperReference(V). Returns true if this reference has a thisValue component.

    -
    • -
- -

The following abstract operations are used in this specification to operate on references:

-
- -
-

6.2.3.1 GetValue - (V)

-
    -
  1. ReturnIfAbrupt(V).
    2. -
  2. If Type(V) is not Reference, return V.
    3. -
  3. Let base be GetBase(V).
    4. -
  4. If IsUnresolvableReference(V), throw a ReferenceError - exception.
    5. -
  5. If IsPropertyReference(V), then -
      -
    1. If HasPrimitiveBase(V) is true, then -
        -
      1. Assert: In this case, base will never be null or - undefined.
        2. -
      2. Let base be ToObject(base).
        3. -
      -
      2. -
    2. Return the result of calling the [[Get]] internal method of base passing GetReferencedName(V) and GetThisValue(V) as the arguments.
      3. -
    -
    6. -
  6. Else base must be an environment record, -
      -
    1. Return the result of calling the GetBindingValue (see 8.1.1) concrete - method of base passing GetReferencedName(V) and IsStrictReference(V) as arguments.
      2. -
    -
    7. -
- -
-

NOTE The object that may be created in step 5.a.ii is not accessible outside of the above - abstract operation and the ordinary object [[Get]] internal method. An implementation might choose to avoid the actual - creation of the object.

-
-
- -
-

6.2.3.2 PutValue - (V, W)

-
    -
  1. ReturnIfAbrupt(V).
    2. -
  2. ReturnIfAbrupt(W).
    3. -
  3. If Type(V) is not Reference, throw a ReferenceError exception.
    4. -
  4. Let base be GetBase(V).
    5. -
  5. If IsUnresolvableReference(V), then -
      -
    1. If IsStrictReference(V) is true, then -
        -
      1. Throw ReferenceError exception.
        2. -
      -
      2. -
    2. Let globalObj be the result of the abstract operation GetGlobalObject.
      3. -
    3. Return Put(globalObj,GetReferencedName(V), W, false).
      4. -
    -
    6. -
  6. Else if IsPropertyReference(V), then -
      -
    1. If HasPrimitiveBase(V) is true, then -
        -
      1. Assert: In this case, base will never be null or - undefined.
        2. -
      2. Set base to ToObject(base).
        3. -
      -
      2. -
    2. Let succeeded be the result of calling the [[Set]] internal method of base passing GetReferencedName(V), W, and GetThisValue(V) as arguments.
      3. -
    3. ReturnIfAbrupt(succeeded).
      4. -
    4. If succeeded is false and IsStrictReference(V) is true, then throw a - TypeError exception.
      5. -
    5. Return.
      6. -
    -
    7. -
  7. Else base must be a Reference whose base is an environment - record. -
      -
    1. Return the result of calling the SetMutableBinding (8.1.1) concrete - method of base, passing GetReferencedName(V), - W, and IsStrictReference(V) as arguments.
      2. -
    -
    8. -
- -
-

NOTE The object that may be created in step 6.a.ii is not accessible outside of the above - algorithm and the ordinary object [[Set]] internal method. An implementation might choose to avoid the actual creation - of that object.

-
-
- -
-

6.2.3.3 - GetThisValue (V)

-
    -
  1. Assert: IsPropertyReference(V) is true.
    2. -
  2. If IsSuperReference(V), then -
      -
    1. Return the value of the thisValue component of the reference V.
      2. -
    -
    3. -
  3. Return GetBase(V).
    4. -
-
-
- -
-
-

6.2.4 The Property Descriptor Specification Type

- -

The Property Descriptor type is used to explain the manipulation and reification of Object property attributes. Values - of the Property Descriptor type are Records. Except for the optional [[Origin]] field, each field’s name is an - attribute name and its value is a corresponding attribute value as specified in 6.1.7.1. In addition, any field may be present or absent. The schema name used within - this specification to tag literal descriptions of Property Descriptor records is “PropertyDescriptor”.

- -

Property Descriptor values may be further classified as data Property Descriptors and accessor Property Descriptors - based upon the existence or use of certain fields. A data Property Descriptor is one that includes any fields named either - [[Value]] or [[Writable]]. An accessor Property Descriptor is one that includes any fields named either [[Get]] or - [[Set]]. Any Property Descriptor may have fields named [[Enumerable]] and [[Configurable]]. A Property Descriptor value - may not be both a data Property Descriptor and an accessor Property Descriptor; however, it may be neither. A generic - Property Descriptor is a Property Descriptor value that is neither a data Property Descriptor nor an accessor Property - Descriptor. A fully populated Property Descriptor is one that is either an accessor Property Descriptor or a data Property - Descriptor and that has all of the fields that correspond to the property attributes defined in either Table 2 or Table 3.

- -

A Property Descriptor may be derived from an object that has properties that directly correspond to the fields of a - Property Descriptor. Such a derived Property Descriptor has an additional field named [[Origin]] whose value is the object - from which the Property Descriptor was derived.

- -

The following abstract operations are used in this specification to operate upon Property Descriptor values:

-
- -
-

6.2.4.1 IsAccessorDescriptor ( Desc )

- -

When the abstract operation IsAccessorDescriptor is called with Property Descriptor Desc, the following - steps are taken:

- -
    -
  1. If Desc is undefined, then return false.
    2. -
  2. If both Desc.[[Get]] and Desc.[[Set]] are absent, then return false.
    3. -
  3. Return true.
    4. -
-
- -
-

6.2.4.2 - IsDataDescriptor ( Desc )

- -

When the abstract operation IsDataDescriptor is called with Property Descriptor Desc, the following - steps are taken:

- -
    -
  1. If Desc is undefined, then return false.
    2. -
  2. If both Desc.[[Value]] and Desc.[[Writable]] are absent, then return false.
    3. -
  3. Return true.
    4. -
-
- -
-

6.2.4.3 IsGenericDescriptor ( Desc )

- -

When the abstract operation IsGenericDescriptor is called with Property Descriptor Desc, the following - steps are taken:

- -
    -
  1. If Desc is undefined, then return false.
    2. -
  2. If IsAccessorDescriptor(Desc) and IsDataDescriptor(Desc) are both false, then return true.
    3. -
  3. Return false.
    4. -
-
- -
-

6.2.4.4 FromPropertyDescriptor ( Desc )

- -

When the abstract operation FromPropertyDescriptor is called with Property Descriptor Desc, the following - steps are taken:

- -
    -
  1. If Desc is undefined, then return undefined.
    2. -
  2. If Desc has an [[Origin]] field, then return Desc.[[Origin]].
    3. -
  3. Let obj be ObjectCreate(%ObjectPrototype%).
    4. -
  4. Assert: obj is an extensible ordinary object with no own - properties.
    5. -
  5. If Desc has a [[Value]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj, - "value", and PropertyDescriptor{[[Value]]: Desc.[[Value]], [[Writable]]: true, - [[Enumerable]]: true, [[Configurable]]: true}
      2. -
    -
    6. -
  6. If Desc has a [[Writable]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj, - "writable", and PropertyDescriptor{[[Value]]: Desc.[[Writable]], [[Writable]]: true, - [[Enumerable]]: true, [[Configurable]]: true}.
      2. -
    -
    7. -
  7. If Desc has a [[Get]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj, - "get", and PropertyDescriptor{[[Value]]: Desc.[[Get]], [[Writable]]: true, - [[Enumerable]]: true, [[Configurable]]: true}.
      2. -
    -
    8. -
  8. If Desc has a [[Set]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj, - "set", and PropertyDescriptor{[[Value]]: Desc.[[Set]], [[Writable]]: true, - [[Enumerable]]: true, [[Configurable]]: true}.
      2. -
    -
    9. -
  9. If Desc has an [[Enumerable]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj, - "enumerable", and PropertyDescriptor{[[Value]]: Desc.[[Enumerable]], [[Writable]]: - true, [[Enumerable]]: true, [[Configurable]]: true}.
      2. -
    -
    10. -
  10. If Desc has a [[Configurable]] field, then -
      -
    1. Call OrdinaryDefineOwnProperty with arguments obj , - "configurable", and PropertyDescriptor{[[Value]]: Desc.[[Configurable]], [[Writable]]: - true, [[Enumerable]]: true, [[Configurable]]: true}.
      2. -
    -
    11. -
  11. Return obj.
    12. -
-
- -
-

6.2.4.5 ToPropertyDescriptor ( Obj )

- -

When the abstract operation ToPropertyDescriptor is called with object Obj, the following steps - are taken:

- -
    -
  1. ReturnIfAbrupt(Obj).
    2. -
  2. If Type(Obj) is not Object throw a TypeError - exception.
    3. -
  3. Let desc be a new Property Descriptor that - initially has no fields.
    4. -
  4. If HasProperty(Obj, "enumerable") is true, then -
      -
    1. Let enum be Get(Obj, "enumerable").
      2. -
    2. ReturnIfAbrupt(enum).
      3. -
    3. Set the [[Enumerable]] field of desc to ToBoolean(enum).
      4. -
    -
    5. -
  5. If HasProperty(Obj, "configurable") is true, then -
      -
    1. Let conf be Get(Obj, "configurable").
      2. -
    2. ReturnIfAbrupt(conf).
      3. -
    3. Set the [[Configurable]] field of desc to ToBoolean(conf).
      4. -
    -
    6. -
  6. If HasProperty(Obj, "value") is true, then -
      -
    1. Let value be Get(Obj, "value").
      2. -
    2. ReturnIfAbrupt(value).
      3. -
    3. Set the [[Value]] field of desc to value.
      4. -
    -
    7. -
  7. If HasProperty(Obj, "writable") is true, then -
      -
    1. Let writable be Get(Obj, "writable").
      2. -
    2. ReturnIfAbrupt(writable).
      3. -
    3. Set the [[Writable]] field of desc to ToBoolean(writable).
      4. -
    -
    8. -
  8. If HasProperty(Obj, "get") is true, then -
      -
    1. Let getter be Get(Obj, "get").
      2. -
    2. ReturnIfAbrupt(getter).
      3. -
    3. If IsCallable(getter) is false and getter is not - undefined, then throw a TypeError exception.
      4. -
    4. Set the [[Get]] field of desc to getter.
      5. -
    -
    9. -
  9. If HasProperty(Obj, "set") is true, then -
      -
    1. Let setter be Get(Obj, "set").
      2. -
    2. ReturnIfAbrupt(setter).
      3. -
    3. If IsCallable(setter) is false and setter is not - undefined, then throw a TypeError exception.
      4. -
    4. Set the [[Set]] field of desc to setter.
      5. -
    -
    10. -
  10. If either desc.[[Get]] or desc.[[Set]] are present, then -
      -
    1. If either desc.[[Value]] or desc.[[Writable]] are present, then throw a TypeError - exception.
      2. -
    -
    11. -
  11. Set the [[Origin]] field of desc to Obj.
    12. -
  12. Return desc.
    13. -
-
- -
-

6.2.4.6 CompletePropertyDescriptor ( Desc, LikeDesc )

- -

When the abstract operation CompletePropertyDescriptor is called with Property Descriptors Desc - and LikeDesc the following steps are taken:

- -
    -
  1. Assert: LikeDesc is either a Property Descriptor or undefined.
    2. -
  2. ReturnIfAbrupt(Desc).
    3. -
  3. Assert: Desc is a Property Descriptor
    4. -
  4. If LikeDesc is undefined, then -
      -
    1. Let like be Record{[[Value]]: undefined, [[Writable]]: false, [[Get]]: undefined, - [[Set]]: undefined, [[Enumerable]]: false, [[Configurable]]: false}.
      2. -
    -
    5. -
  5. else, -
      -
    1. Let like be a new Property Descriptor that is a - copy of LikeDesc.
      2. -
    2. Perform CompletePropertyDescriptor(like, undefined).
      3. -
    -
    6. -
  6. If either IsGenericDescriptor(Desc) or IsDataDescriptor(Desc) is true, then -
      -
    1. If Desc does not have a [[Value]] field, then set Desc.[[Value]] to like.[[Value]].
      2. -
    2. If Desc does not have a [[Writable]] field, then set Desc.[[Writable]] to - like.[[Writable]].
      3. -
    -
    7. -
  7. Else, -
      -
    1. If Desc does not have a [[Get]] field, then set Desc.[[Get]] to like.[[Get]].
      2. -
    2. If Desc does not have a [[Set]] field, then set Desc.[[Set]] to like.[[Set]].
      3. -
    -
    8. -
  8. If Desc does not have an [[Enumerable]] field, then set Desc.[[Enumerable]] to - like.[[Enumerable]].
    9. -
  9. If Desc does not have a [[Configurable]] field, then set Desc.[[Configurable]] to - like.[[Configurable]].
    10. -
  10. Return Desc.
    11. -
-
-
- -
-

6.2.5 The Lexical Environment and Environment Record Specification Types

- -

The Lexical Environment and Environment - Record types are used to explain the behaviour of name resolution in nested functions and blocks. These types and the - operations upon them are defined in 8.1.

-
- -
-
-

6.2.6 Data - Blocks

- -

The Data Block specification type is used to describe a distinct and mutable sequence of byte-sized (8 bit) numeric - values. A Data Block value is created with a fixed number of bytes that each have the initial value 0.

- -

For notational convenience within this specification, an array-like syntax can be used to express to the individual - bytes of a Data Block value. This notation presents a Data Block value as a 0-origined integer indexed sequence of bytes. - For example, if db is a 5 byte Data Block value then db[2] can be used to express access to its - 3rd byte.

- -

The following abstract operations are used in this specification to operate upon Data Block values:

-
- -
-

6.2.6.1 CreateByteDataBlock(size)

- -

When the abstract operation CreateByteDataBlock is called with integer argument size, the following steps - are taken:

- -
    -
  1. Assert: size≥0.
    2. -
  2. Let db be a new Data Block value consisting of size bytes. If it is - impossible to create such a Data Block, then throw a RangeError - exception.
    3. -
  3. Set all of the bytes of db to 0.
    4. -
  4. Return db.
    5. -
-
- -
-

6.2.6.2 CopyDataBlockBytes(toBlock, toIndex, fromBlock, fromIndex, count)

- -

When the abstract operation CopyDataBlockBytes is called the following steps are taken:

- -
    -
  1. Assert: fromBlock and toBlock are distinct Data Block values.
    2. -
  2. Assert: fromIndex, toIndex, and count are positive - integer values.
    3. -
  3. Let fromSize be the number of bytes in fromBlock.
    4. -
  4. Assert: fromIndex+count ≤ fromSize.
    5. -
  5. Let toSize be the number of bytes in toBlock.
    6. -
  6. Assert: toIndex+count ≤ toSize.
    7. -
  7. Repeat, while count>0 -
      -
    1. Set toBlock[toIndex] to the value of fromBlock[fromIndex].
      2. -
    2. Increment toIndex and fromIndex each by 1.
      3. -
    3. Decrement count by 1.
      4. -
    -
    8. -
  8. Return NormalCompletion(empty)
    9. -
-
-
-
-
- -
-
-

7 Abstract - Operations

- -

These operations are not a part of the ECMAScript language; they are defined here to solely to aid the specification of the - semantics of the ECMAScript language. Other, more specialized abstract operations are defined throughout this - specification.

-
- -
-
-

7.1 - Type Conversion and Testing

- -

The ECMAScript language implicitly performs automatic type conversion as needed. To clarify the semantics of certain - constructs it is useful to define a set of conversion abstract operations. The conversion abstract operations are - polymorphic; they can accept a value of any ECMAScript language type or of a Completion Record value. But no other specification types are used - with these operations.

-
- -
-

7.1.1 - ToPrimitive

- -

The abstract operation ToPrimitive takes an input argument and an optional argument PreferredType. The abstract operation ToPrimitive converts its input argument to a non-Object - type. If an object is capable of converting to more than one primitive type, it may use the optional hint PreferredType to favour that type. Conversion occurs according to Table 9:

- -
-
Table 9 — ToPrimitive Conversions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Input TypeResult
Completion RecordIf input is an abrupt completion, return input. Otherwise return ToPrimitive(input.[[value]]) also passing the optional hint PreferredType.
UndefinedReturn input (no conversion).
NullReturn input (no conversion).
BooleanReturn input (no conversion).
NumberReturn input (no conversion).
StringReturn input (no conversion).
SymbolReturn input (no conversion).
ObjectPerform the steps following this table.
-
- -

When Type(input) is Object, the following steps are taken:

- -
    -
  1. If PreferredType was not passed, let hint be "default".
    2. -
  2. Else if PreferredType is hint String, let hint be "string".
    3. -
  3. Else PreferredType is hint Number, let hint be "number".
    4. -
  4. Let exoticToPrim be GetMethod(input, @@toPrimitive).
    5. -
  5. ReturnIfAbrupt(exoticToPrim).
    6. -
  6. If exoticToPrim is not undefined, then -
      -
    1. Let result be the result of calling the [[Call]] internal method of exoticToPrim, with input - as thisArgument and (hint) as argumentsList.
      2. -
    2. ReturnIfAbrupt(result).
      3. -
    3. If result is an ECMAScript language value and Type(result) is not Object, then return - result.
      4. -
    4. Else, throw a TypeError exception.
      5. -
    -
    7. -
  7. If hint is "default" then, let hint be "number".
    8. -
  8. Return OrdinaryToPrimitive(input,hint).
    9. -
- -

When the abstract operation OrdinaryToPrimitive is called with arguments O and hint, the following - steps are taken:

- -
    -
  1. Assert: Type(O) is - Object
    2. -
  2. Assert: Type(hint) - is String and its value is either "string" or "number".
    3. -
  3. If hint is "string", then -
      -
    1. Let methodNames be the List ( - "toString", "valueOf").
      2. -
    -
    4. -
  4. Else, -
      -
    1. Let methodNames be the List ( "valueOf", - "toString").
      2. -
    -
    5. -
  5. For each name in methodNames in List order, do -
      -
    1. Let method be Get(O, name).
      2. -
    2. ReturnIfAbrupt(method).
      3. -
    3. If IsCallable(method) is true then, -
        -
      1. Let result be the result of calling the [[Call]] internal method of method, with O as - thisArgument and an empty List as - argumentsList.
        2. -
      2. ReturnIfAbrupt(result).
        3. -
      3. If Type(result) is not Object, then return - result.
        4. -
      -
      4. -
    -
    6. -
  6. Throw a TypeError exception.
    7. -
- -
-

NOTE When ToPrimitive is called with no hint, then it generally behaves as if the hint were - Number. However, objects may over-ride this behaviour by defining a @@toPrimitive method. Of the objects defined in this - specification only Date objects (see 20.3) and Symbol objects (see 19.4.3.4) over-ride the default ToPrimitive behaviour. Date objects - treat no hint as if the hint were String.

-
-
- -
-

7.1.2 - ToBoolean

- -

The abstract operation ToBoolean converts its argument to a value of type Boolean according to Table 10:

- -
-
Table 10 — ToBoolean Conversions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Argument TypeResult
Completion RecordIf argument is an abrupt completion, return the argument. Otherwise return ToBoolean(argument.[[value]])
UndefinedReturn false
NullReturn false
BooleanReturn the input argument (no conversion).
NumberReturn false if the argument is +0, −0, or NaN; otherwise return true.
StringReturn false if the argument is the empty String (its length is zero); otherwise return true.
SymbolReturn true
ObjectReturn true
-
-
- -
-
-

7.1.3 - ToNumber

- -

The abstract operation ToNumber converts its argument to a value of type Number according to Table 11:

- -
-
Table 11 — ToNumber Conversions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Argument TypeResult
Completion RecordIf argument is an abrupt completion, return argument. Otherwise return ToNumber(argument.[[value]])
UndefinedReturn NaN
NullReturn +0
BooleanReturn 1 if argument is true. Return +0 if argument is false.
NumberReturn argument (no conversion).
StringSee grammar and conversion algorithm below.
SymbolReturn NaN
Object -

Apply the following steps:

- -
    -
  1. Let primValue be ToPrimitive(argument, hint Number).
    2. -
  2. Return ToNumber(primValue).
    3. -
-
-
-
- -
-
-

7.1.3.1 ToNumber Applied to the String Type

- -

ToNumber applied to Strings applies the following grammar to the input String. If the - grammar cannot interpret the String as an expansion of StringNumericLiteral, then the result of - ToNumber is NaN.

- -

Syntax

- -
-
StringNumericLiteral :::
-
StrWhiteSpaceopt
-
StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt
-
- -
-
StrWhiteSpace :::
-
StrWhiteSpaceChar StrWhiteSpaceopt
-
- -
-
StrWhiteSpaceChar :::
-
WhiteSpace
-
LineTerminator
-
- -
-
StrNumericLiteral :::
-
StrDecimalLiteral
-
HexIntegerLiteral
-
- -
-
StrDecimalLiteral :::
-
StrUnsignedDecimalLiteral
-
+ StrUnsignedDecimalLiteral
-
- StrUnsignedDecimalLiteral
-
- -
-
StrUnsignedDecimalLiteral :::
-
Infinity
-
DecimalDigits . DecimalDigitsopt ExponentPartopt
-
. DecimalDigits ExponentPartopt
-
DecimalDigits ExponentPartopt
-
- -
-
DecimalDigits :::
-
DecimalDigit
-
DecimalDigits DecimalDigit
-
- -
-
DecimalDigit ::: one of
-
0 1 2 3 4 5 6 7 8 9
-
- -
-
ExponentPart :::
-
ExponentIndicator SignedInteger
-
- -
-
ExponentIndicator ::: one of
-
e E
-
- -
-
SignedInteger :::
-
DecimalDigits
-
+ DecimalDigits
-
- DecimalDigits
-
- -
-
HexIntegerLiteral :::
-
0x HexDigit
-
0X HexDigit
-
HexIntegerLiteral HexDigit
-
- -
-
HexDigit ::: one of
-
0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
-
- -
-

NOTE Some differences should be noted between the syntax of a StringNumericLiteral - and a NumericLiteral (see 11.8.3):

- -
    -
  • -

    A StringNumericLiteral may include leading and/or trailing white space and/or line terminators.

    -
    • - -
  • -

    A StringNumericLiteral that is decimal may have any number of leading 0 digits.

    -
    • - -
  • -

    A StringNumericLiteral that is decimal may include a + or - to indicate its - sign.

    -
    • - -
  • -

    A StringNumericLiteral that is empty or contains only white space is converted to +0.

    -
    • - -
  • -

    Infinity and –Infinity are recognized as a StringNumericLiteral but not - as a NumericLiteral.

    -
    • -
-
-
- -
-

7.1.3.1.1 Runtime Semantics: MV’s

- -

The conversion of a String to a Number value is similar overall to the determination of the Number value for a - numeric literal (see 11.8.3), but some of the details are different, so the - process for converting a String numeric literal to a value of Number type is given here in full. This value is - determined in two steps: first, a mathematical value (MV) is derived from the String numeric literal; second, this - mathematical value is rounded as described below.

- -
    -
  • -

    The MV of StringNumericLiteral ::: [empty] is 0.

    -
    • - -
  • -

    The MV of StringNumericLiteral ::: StrWhiteSpace is 0.

    -
    • - -
  • -

    The MV of StringNumericLiteral ::: StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt is the MV of StrNumericLiteral, no - matter whether white space is present or not.

    -
    • - -
  • -

    The MV of StrNumericLiteral ::: StrDecimalLiteral is the MV of StrDecimalLiteral.

    -
    • - -
  • -

    The MV of StrNumericLiteral ::: HexIntegerLiteral is the MV of HexIntegerLiteral.

    -
    • - -
  • -

    The MV of StrDecimalLiteral ::: StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral.

    -
    • - -
  • -

    The MV of StrDecimalLiteral ::: + StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral.

    -
    • - -
  • -

    The MV of StrDecimalLiteral ::: - StrUnsignedDecimalLiteral is the negative of the MV of StrUnsignedDecimalLiteral. (Note that if the MV of StrUnsignedDecimalLiteral is 0, the negative of this MV is also 0. The rounding rule described - below handles the conversion of this signless mathematical zero to a floating-point +0 or −0 as - appropriate.)

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: Infinity is 1010000 (a value - so large that it will round to +∞).

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits . is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits . DecimalDigits is the MV of - the first DecimalDigits plus (the MV of the second DecimalDigits - times 10−n), where n is the - number of characters in the second DecimalDigits.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits . ExponentPart is the MV of - DecimalDigits times 10e, where e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits . DecimalDigits ExponentPart is (the MV of the first DecimalDigits plus (the MV of the second - DecimalDigits times 10−n)) times 10e, where n is the number - of characters in the second DecimalDigits and e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: . DecimalDigits is the MV of DecimalDigits times - 10−n, where n is the number of characters in DecimalDigits.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: . DecimalDigits ExponentPart is the MV of - DecimalDigits times 10e−n, where n is the number of characters in - DecimalDigits and e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of StrUnsignedDecimalLiteral ::: DecimalDigits ExponentPart is the MV of DecimalDigits times - 10e, where e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of DecimalDigits ::: DecimalDigit is the MV of DecimalDigit.

    -
    • - -
  • -

    The MV of DecimalDigits ::: DecimalDigits DecimalDigit is (the MV of DecimalDigits times - 10) plus the MV of DecimalDigit.

    -
    • - -
  • -

    The MV of ExponentPart ::: ExponentIndicator SignedInteger is the MV of - SignedInteger.

    -
    • - -
  • -

    The MV of SignedInteger ::: DecimalDigits is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of SignedInteger ::: + DecimalDigits is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of SignedInteger ::: - DecimalDigits is the negative of the MV of - DecimalDigits.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 0 or of HexDigit ::: - 0 is 0.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 1 or of HexDigit ::: - 1 is 1.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 2 or of HexDigit ::: - 2 is 2.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 3 or of HexDigit ::: - 3 is 3.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 4 or of HexDigit ::: - 4 is 4.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 5 or of HexDigit ::: - 5 is 5.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 6 or of HexDigit ::: - 6 is 6.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 7 or of HexDigit ::: - 7 is 7.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 8 or of HexDigit ::: - 8 is 8.

    -
    • - -
  • -

    The MV of DecimalDigit ::: 9 or of HexDigit ::: - 9 is 9.

    -
    • - -
  • -

    The MV of HexDigit ::: a or of HexDigit ::: - A is 10.

    -
    • - -
  • -

    The MV of HexDigit ::: b or of HexDigit ::: - B is 11.

    -
    • - -
  • -

    The MV of HexDigit ::: c or of HexDigit ::: - C is 12.

    -
    • - -
  • -

    The MV of HexDigit ::: d or of HexDigit ::: - D is 13.

    -
    • - -
  • -

    The MV of HexDigit ::: e or of HexDigit ::: - E is 14.

    -
    • - -
  • -

    The MV of HexDigit ::: f or of HexDigit ::: - F is 15.

    -
    • - -
  • -

    The MV of HexIntegerLiteral ::: 0x HexDigit is the MV of HexDigit.

    -
    • - -
  • -

    The MV of HexIntegerLiteral ::: 0X HexDigit is the MV of HexDigit.

    -
    • - -
  • -

    The MV of HexIntegerLiteral ::: HexIntegerLiteral HexDigit is (the MV of HexIntegerLiteral - times 16) plus the MV of HexDigit.

    -
    • -
- -

Once the exact MV for a String numeric literal has been determined, it is then rounded to a value of the Number type. - If the MV is 0, then the rounded value is +0 unless the first non white space character in the String numeric literal is - ‘-’, in which case the rounded value is −0. Otherwise, the rounded value must be the - Number value for the MV (in the sense defined in 6.1.6), unless - the literal includes a StrUnsignedDecimalLiteral and the literal has more than 20 significant - digits, in which case the Number value may be either the Number value for the MV of a literal produced by replacing each - significant digit after the 20th with a 0 digit or the Number value for the MV of a literal produced by replacing each - significant digit after the 20th with a 0 digit and then incrementing the literal at the 20th digit position. A digit is - significant if it is not part of an ExponentPart and

- -
    -
  • it is not 0; or
    • -
  • there is a nonzero digit to its left and there is a nonzero digit, not in the ExponentPart, to its right.
    • -
-
-
-
- -
-

7.1.4 - ToInteger

- -

The abstract operation ToInteger converts its argument to an integral numeric value. This abstract operation - functions as follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, return +0.
    4. -
  4. If number is +0, −0, +∞, or −∞, return number.
    5. -
  5. Return the result of computing sign(number) × floor(abs(number)).
    6. -
-
- -
-

7.1.5 ToInt32: - (Signed 32 Bit Integer)

- -

The abstract operation ToInt32 converts its argument to one of 232 integer values in the range −231 through 231−1, - inclusive. This abstract operation functions as follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return - +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int32bit be int modulo 232.
    6. -
  6. If int32bit ≥ 231, return int32bit − 232, otherwise return - int32bit.
    7. -
- -
-

NOTE Given the above definition of ToInt32:

- -
    -
  • -

    The ToInt32 abstract operation is idempotent: if applied to a result that it produced, the second application - leaves that value unchanged.

    -
    • - -
  • -

    ToInt32(ToUint32(x)) is equal to ToInt32(x) for all values of x. - (It is to preserve this latter property that +∞ and −∞ are mapped to +0.)

    -
    • - -
  • -

    ToInt32 maps −0 to +0.

    -
    • -
-
-
- -
-

7.1.6 ToUint32: - (Unsigned 32 Bit Integer)

- -

The abstract operation ToUint32 converts its argument to one of 232 integer values in the range 0 through 232−1, inclusive. This abstract operation functions as - follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int32bit be int modulo 232.
    6. -
  6. Return int32bit.
    7. -
- -
-

NOTE Given the above definition of ToUint32:

- -
    -
  • -

    Step 6 is the only difference between ToUint32 and ToInt32.

    -
    • - -
  • -

    The ToUint32 abstract operation is idempotent: if applied to a result that it produced, the second application - leaves that value unchanged.

    -
    • - -
  • -

    ToUint32(ToInt32(x)) is equal to ToUint32(x) for all values of x. - (It is to preserve this latter property that +∞ and −∞ are mapped to +0.)

    -
    • - -
  • -

    ToUint32 maps −0 to +0.

    -
    • -
-
-
- -
-

7.1.7 ToInt16: - (Signed 16 Bit Integer)

- -

The abstract operation ToInt16 converts its argument to one of 216 integer values in the range −32768 - through 32767, inclusive. This abstract operation functions as - follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return - +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int16bit be int modulo 216.
    6. -
  6. If int16bit ≥ 215, return int16bit − 216, otherwise return - int16bit.
    7. -
-
- -
-

7.1.8 ToUint16: - (Unsigned 16 Bit Integer)

- -

The abstract operation ToUint16 converts its argument to one of 216 integer values in the range 0 through 216−1, inclusive. This abstract operation functions as - follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int16bit be int modulo 216.
    6. -
  6. Return int16bit.
    7. -
- -
-

NOTE Given the above definition of ToUint16:

- -
    -
  • The substitution of 216 for 232 in step 5 is the only difference between ToUint32 and ToUint16.
    • -
  • ToUint16 maps −0 to +0.
    • -
-
-
- -
-

7.1.9 ToInt8: (Signed - 8 Bit Integer)

- -

The abstract operation ToInt8 converts its argument to one of 28 integer values in the range −128 through - 127, inclusive. This abstract operation functions as follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return - +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int8bit be int modulo 28.
    6. -
  6. If int8bit ≥ 27, return int8bit − 28, otherwise return - int8bit.
    7. -
-
- -
-

7.1.10 ToUint8: - (Unsigned 8 Bit Integer)

- -

The abstract operation ToUint8 converts its argument to one of 28 integer values in the range 0 through 255, inclusive. This abstract operation functions as follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, +0, −0, +∞, or −∞, return +0.
    4. -
  4. Let int be sign(number) × floor(abs(number)).
    5. -
  5. Let int8bit be int modulo 28.
    6. -
  6. Return int8bit.
    7. -
-
- -
-

7.1.11 - ToUint8Clamp: (Unsigned 8 Bit Integer, Clamped)

- -

The abstract operation ToUint8Clamp converts its argument to one of 28 integer values in the range 0 through 255, inclusive. This abstract operation functions as follows:

- -
    -
  1. Let number be ToNumber(argument).
    2. -
  2. ReturnIfAbrupt(number).
    3. -
  3. If number is NaN, return +0.
    4. -
  4. If number ≤ 0, return +0.
    5. -
  5. If number ≥ 255, return 255.
    6. -
  6. Let f be floor(number).
    7. -
  7. If f + 0.5 < number, then return f + 1.
    8. -
  8. If number < f + 0.5, then return f.
    9. -
  9. If f is odd, then return f + 1.
    10. -
  10. Return f.
    11. -
- -
-

NOTE Note that unlike the other ECMAScript integer conversion abstract operation, ToUint8Clamp - rounds rather than truncates non-integer values and does not convert +∞ to 0. ToUint8Clamp does “round - half to even” tie-breaking. This differs from Math.round which does - “round half up” tie-breaking.

-
-
- -
-
-

7.1.12 - ToString

- -

The abstract operation ToString converts its argument to a value of type String according to Table 12:

- -
-
Table 12 — ToString Conversions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Argument TypeResult
Completion RecordIf argument is an abrupt completion, return argument. Otherwise return ToString(argument.[[value]])
Undefined"undefined"
Null"null"
Boolean -

If argument is true, then return "true".

- -

If argument is false, then return "false".

-
NumberSee 7.1.12.1.
StringReturn argument (no conversion)
SymbolThrow a TypeError exception.
Object -

Apply the following steps:

- -

1. Let primValue be ToPrimitive(argument, hint String).

- -

2. Return ToString(primValue).

-
-
-
- -
-

7.1.12.1 ToString Applied to the Number Type

- -

The abstract operation ToString converts a Number m to String format as - follows:

- -
    -
  1. If m is NaN, return the String "NaN".
    2. -
  2. If m is +0 or −0, return the String "0".
    3. -
  3. If m is less than zero, return the String concatenation of the String "-" and ToString(−m).
    4. -
  4. If m is +∞, return the String "Infinity".
    5. -
  5. Otherwise, let n, k, and s be integers such that k ≥ 1, 10k−1 - ≤ s < 10k, the Number value for s × 10n−k is - m, and k is as small as possible. Note that k is the number of digits in the decimal - representation of s, that s is not divisible by 10, and that the least significant digit of s - is not necessarily uniquely determined by these criteria.
    6. -
  6. If k ≤ n ≤ 21, return the String consisting of the k digits of the decimal representation - of s (in order, with no leading zeroes), followed by n−k occurrences of the character - ‘0’.
    7. -
  7. If 0 < n ≤ 21, return the String consisting of the most significant n digits of the decimal - representation of s, followed by a decimal point ‘.’, followed by the remaining - k−n digits of the decimal representation of s.
    8. -
  8. If −6 < n ≤ 0, return the String consisting of the character ‘0’, - followed by a decimal point ‘.’, followed by −n occurrences of the character - ‘0’, followed by the k digits of the decimal representation of s.
    9. -
  9. Otherwise, if k = 1, return the String consisting of the single digit of s, followed by lowercase - character ‘e’, followed by a plus sign ‘+’ or minus sign - ‘−’ according to whether n−1 is positive or negative, followed by the - decimal representation of the integer abs(n−1) (with no - leading zeroes).
    10. -
  10. Return the String consisting of the most significant digit of the decimal representation of s, followed by a - decimal point ‘.’, followed by the remaining k−1 digits of the decimal representation of - s, followed by the lowercase character ‘e’, followed by a plus sign - ‘+’ or minus sign ‘−’ according to whether n−1 - is positive or negative, followed by the decimal representation of the integer abs(n−1) (with no leading zeroes).
    11. -
- -
-

NOTE 1 The following observations may be useful as guidelines for implementations, but are - not part of the normative requirements of this Standard:

- -
    -
  • -

    If x is any Number value other than −0, then ToNumber(ToString(x)) is exactly the same Number value as x.

    -
    • - -
  • -

    The least significant digit of s is not always uniquely determined by the requirements listed in step 5.

    -
    • -
-
- -
-

NOTE 2 For implementations that provide more accurate conversions than required by the rules - above, it is recommended that the following alternative version of step 5 be used as a guideline:

- -

Otherwise, let n, k, and s be integers such that k ≥ 1, 10k−1 - ≤ s < 10k, the Number value for s × 10n−k is - m, and k is as small as possible. If there are multiple possibilities for s, choose the value of - s for which s × 10n−k is closest in value to m. If there are - two such possible values of s, choose the one that is even. Note that k is the number of digits in the - decimal representation of s and that s is not divisible by 10.

-
- -
-

NOTE 3 Implementers of ECMAScript may find useful the paper and code written by David M. Gay - for binary-to-decimal conversion of floating-point numbers:

- -

Gay, David M. Correctly Rounded Binary-Decimal and Decimal-Binary Conversions. Numerical Analysis, Manuscript 90-10. - AT&T Bell Laboratories (Murray Hill, New Jersey). November 30, 1990. Available as
http://cm.bell-labs.com/cm/cs/doc/90/4-10.ps.gz. - Associated code available as
http://netlib.sandia.gov/fp/dtoa.c and as
http://netlib.sandia.gov/fp/g_fmt.c and may also be found at the - various netlib mirror sites.

-
-
-
- -
-

7.1.13 - ToObject

- -

The abstract operation ToObject converts its argument to a value of type Object according to Table 13:

- -
-
Table 13 — ToObject Conversions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Argument TypeResult
Completion RecordIf argument is an abrupt completion, return argument. Otherwise return ToObject(argument.[[value]])
UndefinedThrow a TypeError exception.
NullThrow a TypeError exception.
BooleanReturn a new Boolean object whose [[BooleanData]] internal slot is set to the value of argument. See 19.3 for a description of Boolean objects.
NumberReturn a new Number object whose [[NumberData]] internal slot is set to the value of argument. See 20.1 for a description of Number objects.
StringReturn a new String object whose [[StringData]] internal slot is set to the value of argument. See 21.1 for a description of String objects.
SymbolReturn a new Symbol object whose [[SymbolData]] internal slot is set to the value of argument. See 19.4 for a description of Symbol objects.
ObjectReturn argument (no conversion).
-
-
- -
-

7.1.14 - ToPropertyKey

- -

The abstract operation ToPropertyKey converts its argument to a value that can be used as a property key by performing the following steps:

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
  2. If Type(argument) is Symbol, then -
      -
    1. Return argument.
      2. -
    -
    3. -
  3. Return ToString(argument).
    4. -
-
- -
-

7.1.15 - ToLength

- -

The abstract operation ToLength converts its argument to an integer suitable for use as the length of an - array-like object. It performs the following steps:

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
  2. Let len be ToInteger(argument).
    3. -
  3. ReturnIfAbrupt(len).
    4. -
  4. If len ≤ +0, then return +0.
    5. -
  5. Return min(len, 253-1).
    6. -
-
- -
-

7.1.16 CanonicalNumericIndexString(argument)

- -

The abstract operation CanonicalNumericIndexString returns its argument converted to a numeric value if it is - a String representation of a Number that would be produced by ToString, or the string - "-0". Otherwise, it returns undefined. This abstract operation functions as - follows:

- -
    -
  1. Assert: Type(argument) is String.
    2. -
  2. If argument is "-0", then return −0.
    3. -
  3. Let n be ToNumber(argument).
    4. -
  4. If SameValue(ToString(n), argument) is - false, then return undefined.
    5. -
  5. Return n.
    6. -
- -

A canonical numeric string is any String value for which the CanonicalNumericIndexString abstraction operation - does not return undefined.

-
-
- -
-
-

7.2 Testing and Comparison Operations

-
- -
-

7.2.1 - CheckObjectCoercible ( argument )

- -

The abstract operation CheckObjectCoercible throws an error if its argument is a value that cannot be - converted to an Object using ToObject. It is defined by Table 14:

- -
-
Table 14 — CheckObjectCoercible Results
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
argument TypeResult
Completion RecordIf argument is an abrupt completion, return argument. Otherwise return CheckObjectCoercible(argument.[[value]])
UndefinedThrow a TypeError exception.
NullThrow a TypeError exception.
BooleanReturn argument
NumberReturn argument
StringReturn argument
SymbolReturn argument
ObjectReturn argument
-
-
- -
-

7.2.2 IsCallable ( - argument )

- -

The abstract operation IsCallable determines if its argument, which must be an ECMAScript language value or a Completion Record, is a callable function Object according to Table 15:

- -
-
Table 15 — IsCallable Results
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Argument TypeResult
Completion RecordIf argument is an abrupt completion, return argument. Otherwise return IsCallable(argument.[[value]])
UndefinedReturn false.
NullReturn false.
BooleanReturn false.
NumberReturn false.
StringReturn false.
SymbolReturn false.
ObjectIf argument has a [[Call]] internal method, then return true, otherwise return false.
-
-
- -
-

7.2.3 SameValue(x, - y)

- -

The internal comparison abstract operation SameValue(x, y), where x and y are - ECMAScript language values, produces true or false. Such a - comparison is performed as follows:

- -
    -
  1. ReturnIfAbrupt(x).
    2. -
  2. ReturnIfAbrupt(y).
    3. -
  3. If Type(x) is different from Type(y), return false.
    4. -
  4. If Type(x) is Undefined, return true.
    5. -
  5. If Type(x) is Null, return true.
    6. -
  6. If Type(x) is Number, then -
      -
    1. If x is NaN and y is NaN, return true.
      2. -
    2. If x is +0 and y is -0, return false.
      3. -
    3. If x is -0 and y is +0, return false.
      4. -
    4. If x is the same Number value as y, return true.
      5. -
    5. Return false.
      6. -
    -
    7. -
  7. If Type(x) is String, then -
      -
    1. If x and y are exactly the same sequence of code units (same length and same code units in - corresponding positions) return true; otherwise, return false.
      2. -
    -
    8. -
  8. If Type(x) is Boolean, then -
      -
    1. If x and y are both true or both false, then return true; otherwise, return - false.
      2. -
    -
    9. -
  9. If Type(x) is Symbol, then -
      -
    1. If x and y are both the same Symbol value, then return true; otherwise, return - false.
      2. -
    -
    10. -
  10. Return true if x and y are the same Object value. Otherwise, return false.
    11. -
-
- -
-

7.2.4 - SameValueZero(x, y)

- -

The internal comparison abstract operation SameValueZero(x, y), where x and y - are ECMAScript language values, produces true or false. Such a - comparison is performed as follows:

- -
    -
  1. ReturnIfAbrupt(x).
    2. -
  2. ReturnIfAbrupt(y).
    3. -
  3. If Type(x) is different from Type(y), return false.
    4. -
  4. If Type(x) is Undefined, return true.
    5. -
  5. If Type(x) is Null, return true.
    6. -
  6. If Type(x) is Number, then -
      -
    1. If x is NaN and y is NaN, return true.
      2. -
    2. If x is +0 and y is -0, return true.
      3. -
    3. If x is -0 and y is +0, return true.
      4. -
    4. If x is the same Number value as y, return true.
      5. -
    5. Return false.
      6. -
    -
    7. -
  7. If Type(x) is String, then -
      -
    1. If x and y are exactly the same sequence of code units (same length and same code units in - corresponding positions) return true; otherwise, return false.
      2. -
    -
    8. -
  8. If Type(x) is Boolean, then -
      -
    1. If x and y are both true or both false, then return true; otherwise, return - false.
      2. -
    -
    9. -
  9. If Type(x) is Symbol, then -
      -
    1. If x and y are both the same Symbol value, then return true; otherwise, return - false.
      2. -
    -
    10. -
  10. Return true if x and y are the same Object value. Otherwise, return false.
    11. -
- -
-

NOTE SameValueZero differs from SameValue only in its treatment of +0 and -0.

-
-
- -
-

7.2.5 - IsConstructor ( argument )

- -

The abstract operation IsConstructor determines if its argument, which must be an ECMAScript language value or a Completion Record, is a function object with a [[Construct]] internal - method.

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
  2. If Type(argument) is not Object, return false.
    3. -
  3. If argument has a [[Construct]] internal method, return true.
    4. -
  4. Return false.
    5. -
-
- -
-

7.2.6 - IsPropertyKey ( argument )

- -

The abstract operation IsPropertyKey determines if its argument, which must be an ECMAScript language value or a Completion Record, is a value that may be used as a property key.

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
  2. If Type(argument) is String, return true.
    3. -
  3. If Type(argument) is Symbol, return true.
    4. -
  4. Return false.
    5. -
-
- -
-

7.2.7 - IsExtensible (O)

- -

The abstract operation IsExtensible is used to determine whether - additional properties can be added to the object that is O. A Boolean value is returned. This abstract operation - performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Return the result of calling the [[IsExtensible]] internal method of O.
    3. -
-
- -
-

7.2.8 IsInteger ( - argument )

- -

The abstract operation IsInteger determines if its argument is a finite integer numeric value.

- -
    -
  1. ReturnIfAbrupt(argument).
    2. -
  2. If Type(argument) is not Number, return false.
    3. -
  3. If argument is NaN, +∞, or −∞, return false.
    4. -
  4. If floor(abs(argument)) ≠ - abs(argument), then return false.
    5. -
  5. Return true.
    6. -
-
- -
-

7.2.9 Abstract Relational Comparison

- -

The comparison x < y, where x and y are values, produces true, - false, or undefined (which indicates that at least one operand is NaN). In addition to x and - y the algorithm takes a Boolean flag named LeftFirst as a parameter. The flag is used to - control the order in which operations with potentially visible side-effects are performed upon x and - y. It is necessary because ECMAScript specifies left to right evaluation of expressions. The default value of - LeftFirst is true and indicates that the x parameter corresponds to an expression - that occurs to the left of the y parameter’s corresponding expression. If LeftFirst - is false, the reverse is the case and operations must be performed upon y before x. Such a - comparison is performed as follows:

- -
    -
  1. ReturnIfAbrupt(x).
    2. -
  2. ReturnIfAbrupt(y).
    3. -
  3. If the LeftFirst flag is true, then -
      -
    1. Let px be ToPrimitive(x, hint Number).
      2. -
    2. ReturnIfAbrupt(px).
      3. -
    3. Let py be ToPrimitive(y, hint Number).
      4. -
    4. ReturnIfAbrupt(py).
      5. -
    -
    4. -
  4. Else the order of evaluation needs to be reversed to preserve left to right evaluation -
      -
    1. Let py be ToPrimitive(y, hint Number).
      2. -
    2. ReturnIfAbrupt(py).
      3. -
    3. Let px be ToPrimitive(x, hint Number).
      4. -
    4. ReturnIfAbrupt(px).
      5. -
    -
    5. -
  5. If both px and py are Strings, then -
      -
    1. If py is a prefix of px, return false. (A String value p is a prefix of String value - q if q can be the result of concatenating p and some other String r. Note that any - String is a prefix of itself, because r may be the empty String.)
      2. -
    2. If px is a prefix of py, return true.
      3. -
    3. Let k be the smallest nonnegative integer such that the character at position k within px is - different from the character at position k within py. (There must be such a k, for neither - String is a prefix of the other.)
      4. -
    4. Let m be the integer that is the code unit value for the character at position k within - px.
      5. -
    5. Let n be the integer that is the code unit value for the character at position k within - py.
      6. -
    6. If m < n, return true. Otherwise, return false.
      7. -
    -
    6. -
  6. Else, -
      -
    1. Let nx be ToNumber(px). Because px and py are primitive - values evaluation order is not important.
      2. -
    2. Let ny be ToNumber(py).
      3. -
    3. If nx is NaN, return undefined.
      4. -
    4. If ny is NaN, return undefined.
      5. -
    5. If nx and ny are the same Number value, return false.
      6. -
    6. If nx is +0 and ny is −0, return false.
      7. -
    7. If nx is −0 and ny is +0, return false.
      8. -
    8. If nx is +∞, return false.
      9. -
    9. If ny is +∞, return true.
      10. -
    10. If ny is −∞, return false.
      11. -
    11. If nx is −∞, return true.
      12. -
    12. If the mathematical value of nx is less than the mathematical value of ny —note that these - mathematical values are both finite and not both zero—return true. Otherwise, return - false.
      13. -
    -
    7. -
- -
-

NOTE 1 Step 5 differs from step 11 in the algorithm for the addition operator + - (12.7.3) in using “and” instead of “or”.

-
- -
-

NOTE 2 The comparison of Strings uses a simple lexicographic ordering on sequences of code unit - values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and - collating order defined in the Unicode specification. Therefore String values that are canonically equal according to the - Unicode standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form. - Also, note that for strings containing supplementary characters, lexicographic ordering on sequences of UTF-16 code unit - values differs from that on sequences of code point values.

-
-
- -
-

7.2.10 Abstract Equality Comparison

- -

The comparison x == y, where x and y are values, produces true or - false. Such a comparison is performed as follows:

- -
    -
  1. If Type(x) is the same as Type(y), then -
      -
    1. Return the result of performing Strict Equality Comparison x === y.
      2. -
    -
    2. -
  2. If x is null and y is undefined, return true.
    3. -
  3. If x is undefined and y is null, return true.
    4. -
  4. If Type(x) is Number and Type(y) is String,
    return the result of the comparison - x == ToNumber(y).
    5. -
  5. If Type(x) is String and Type(y) is Number,
    return the result of the comparison ToNumber(x) == y.
    6. -
  6. If Type(x) is Boolean, return the result of the comparison - ToNumber(x) == y.
    7. -
  7. If Type(y) is Boolean, return the result of the comparison - x == ToNumber(y).
    8. -
  8. If Type(x) is either String or Number and Type(y) is Object,
    return the result of the comparison - x == ToPrimitive(y).
    9. -
  9. If Type(x) is Object and Type(y) is either String or Number,
    return the result of - the comparison ToPrimitive(x) == y.
    10. -
  10. Return false.
    11. -
-
- -
-

7.2.11 Strict Equality Comparison

- -

The comparison x === y, where x and y are values, produces true or - false. Such a comparison is performed as follows:

- -
    -
  1. If Type(x) is different from Type(y), return false.
    2. -
  2. If Type(x) is Undefined, return true.
    3. -
  3. If Type(x) is Null, return true.
    4. -
  4. If Type(x) is Number, then -
      -
    1. If x is NaN, return false.
      2. -
    2. If y is NaN, return false.
      3. -
    3. If x is the same Number value as y, return true.
      4. -
    4. If x is +0 and y is −0, return true.
      5. -
    5. If x is −0 and y is +0, return true.
      6. -
    6. Return false.
      7. -
    -
    5. -
  5. If Type(x) is String, then -
      -
    1. If x and y are exactly the same sequence of characters (same length and same characters in - corresponding positions), return true.
      2. -
    2. Else, return false.
      3. -
    -
    6. -
  6. If Type(x) is Boolean, then -
      -
    1. If x and y are both true or both false, return true.
      2. -
    2. Else, return false.
      3. -
    -
    7. -
  7. If x and y are the same Symbol value, return true.
    8. -
  8. If x and y are the same Object value, return true.
    9. -
  9. Return false.
    10. -
- -
-

NOTE This algorithm differs from the SameValue Algorithm (7.2.3) in its treatment of signed zeroes and NaNs.

-
-
-
- -
-
-

7.3 - Operations on Objects

-
- -
-

7.3.1 Get (O, P)

- -

The abstract operation Get is used to retrieve the value of a specific - property of an object. The operation is called with arguments O and P where O is the - object and P is the property key. This abstract operation performs the following - steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Return the result of calling the [[Get]] internal method of O passing P and O as the - arguments.
    4. -
-
- -
-

7.3.2 Put (O, - P, V, Throw)

- -

The abstract operation Put is used to set the value of a specific - property of an object. The operation is called with arguments O, P, V, and Throw where O is the object, P is the property key, - V is the new value for the property and Throw is a Boolean flag. This abstract operation - performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Assert: Type(Throw) is Boolean.
    4. -
  4. Let success be the result of calling the [[Set]] internal method of O passing P, V, and - O as the arguments.
    5. -
  5. ReturnIfAbrupt(success).
    6. -
  6. If success is false and Throw is true, then throw a TypeError exception.
    7. -
  7. Return success.
    8. -
-
- -
-

7.3.3 - CreateDataProperty (O, P, V)

- -

The abstract operation CreateDataProperty is used to create a new own - property of an object. The operation is called with arguments O, P, and V where - O is the object, P is the property key, and V is the value - for the property. This abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let newDesc be the PropertyDescriptor{[[Value]]: V, [[Writable]]: true, [[Enumerable]]: - true, [[Configurable]]: true}.
    4. -
  4. Return the result of calling the [[DefineOwnProperty]] internal method of O passing P and newDesc - as arguments.
    5. -
- -
-

NOTE This abstract operation creates a property whose attributes are set to the same defaults - used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. - If it does exist and is not configurable or O is not extensible [[DefineOwnProperty]] will return false.

-
-
- -
-

7.3.4 CreateDataPropertyOrThrow (O, P, V)

- -

The abstract operation CreateDataPropertyOrThrow is used to create a - new own property of an object. It throws a TypeError exception if the requested property update - cannot be performed. The operation is called with arguments O, P, and V where O - is the object, P is the property key, and V is the value for the - property. This abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let success be CreateDataProperty(O, P, V).
    4. -
  4. ReturnIfAbrupt(success).
    5. -
  5. If success is false, then throw a TypeError exception.
    6. -
  6. Return success.
    7. -
- -
-

NOTE This abstract operation creates a property whose attributes are set to the same defaults - used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. - If it does exist and is not configurable or O is not extensible [[DefineOwnProperty]] will return false - causing this operation to throw a TypeError exception.

-
-
- -
-

7.3.5 - DefinePropertyOrThrow (O, P, desc)

- -

The abstract operation DefinePropertyOrThrow is used to call the - [[DefineOwnProperty]] internal method of an object in a manner that will throw a TypeError exception if the requested - property update cannot be performed. The operation is called with arguments O, P, and - desc where O is the object, P is the property key, and - desc is the Property Descriptor for the property. This - abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let success be the result of calling the [[DefineOwnProperty]] internal method of O passing P - and desc as arguments.
    4. -
  4. ReturnIfAbrupt(success).
    5. -
  5. If success is false, then throw a TypeError exception.
    6. -
  6. Return success.
    7. -
-
- -
-

7.3.6 - DeletePropertyOrThrow (O, P)

- -

The abstract operation DeletePropertyOrThrow is used to remove a specific own property of an object. It throws an - exception if the property is not configurable. The operation is called with arguments O and P where - O is the object and P is the property key. This abstract operation - performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let success be the result of calling the [[Delete]] internal method of O passing P as the - argument.
    4. -
  4. ReturnIfAbrupt(success).
    5. -
  5. If success is false, then throw a TypeError exception.
    6. -
  6. Return success.
    7. -
-
- -
-

7.3.7 GetMethod (O, - P)

- -

The abstract operation GetMethod is used to get the value of a specific property of an object when the value of the - property is expected to be a function. The operation is called with arguments O and P where - O is the object, P is the property key. This abstract operation - performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let func be the result of calling the [[Get]] internal method of O passing P and O as the - arguments.
    4. -
  4. ReturnIfAbrupt(func).
    5. -
  5. If func is undefined, then return undefined.
    6. -
  6. If IsCallable(func) is false, then throw a TypeError - exception.
    7. -
  7. Return func.
    8. -
-
- -
-

7.3.8 HasProperty - (O, P)

- -

The abstract operation HasProperty is used to determine whether an object has a property with the specified property key. The property may be either an own or inherited. A Boolean value is returned. The - operation is called with arguments O and P where O is the object and P is the - property key. This abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Return the result of calling the [[HasProperty]] internal method of O with argument P.
    4. -
-
- -
-

7.3.9 - HasOwnProperty (O, P)

- -

The abstract operation HasOwnProperty is used to determine whether an object has an own property with the specified property key. A Boolean value is returned. The operation is called with arguments O - and P where O is the object and P is the property key. This - abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: IsPropertyKey(P) is - true.
    3. -
  3. Let desc be the result of calling the [[GetOwnProperty]] internal method of O passing P as the - argument.
    4. -
  4. ReturnIfAbrupt(desc).
    5. -
  5. If desc is undefined, return false.
    6. -
  6. Return true.
    7. -
-
- -
-

7.3.10 Invoke(O,P, - [args])

- -

The abstract operation Invoke is used to call a method property of an - object. The operation is called with arguments O, P , and optionally args where - O serves as both the lookup point for the property and the this value of the call, P is the property key, and args is the list of arguments values passed to the method. If - args is not present, an empty List is used as its value. - This abstract operation performs the following steps:

- -
    -
  1. Assert: P is a valid property key.
    2. -
  2. If args was not passed, then let args be a new empty List.
    3. -
  3. Let obj be ToObject(O).
    4. -
  4. ReturnIfAbrupt(obj).
    5. -
  5. Let func be the result of calling the [[Get]] internal method of obj passing P and O as - the arguments.
    6. -
  6. ReturnIfAbrupt(func).
    7. -
  7. If IsCallable(func) is false, then throw a TypeError - exception.
    8. -
  8. Return the result of calling the [[Call]] internal method of func passing O as thisArgument and - args as argumentsList.
    9. -
-
- -
-

7.3.11 - SetIntegrityLevel (O, level)

- -

The abstract operation SetIntegrityLevel is used to fix the set of own - properties of an object. This abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: level is either "sealed" or - "frozen".
    3. -
  3. Let keysArray be the result of calling the [[OwnPropertyKeys]] internal method of O.
    4. -
  4. Let keys be CreateListFromArrayLike(keysArray).
    5. -
  5. ReturnIfAbrupt(keys).
    6. -
  6. Let pendingException be undefined.
    7. -
  7. If level is "sealed", then -
      -
    1. Repeat for each element k of keys, -
        -
      1. Let status be DefinePropertyOrThrow(O, k, - PropertyDescriptor{ [[Configurable]]: false}).
        2. -
      2. If status is an abrupt completion, then -
          -
        1. If pendingException is undefined, then set pendingException to status.
          2. -
        -
        3. -
      -
      2. -
    -
    8. -
  8. Else level is "frozen", -
      -
    1. Repeat for each element k of keys, -
        -
      1. Let status be the result of calling the [[GetOwnProperty]] internal method of O with - k.
        2. -
      2. If status is an abrupt completion, then -
          -
        1. If pendingException is undefined, then set pendingException to status.
          2. -
        -
        3. -
      3. Else, -
          -
        1. Let currentDesc be status.[[value]].
          2. -
        2. If currentDesc is not undefined, then -
            -
          1. If IsAccessorDescriptor(currentDesc) is true, - then -
              -
            1. Let desc be the PropertyDescriptor{[[Configurable]]: false}.
              2. -
            -
            2. -
          2. Else, -
              -
            1. Let desc be the PropertyDescriptor { [[Configurable]]: false, [[Writable]]: - false }.
              2. -
            -
            3. -
          3. Let status be DefinePropertyOrThrow(O, - k, desc).
            4. -
          4. If status is an abrupt completion, then -
              -
            1. If pendingException is undefined, then set pendingException to - status.
              2. -
            -
            5. -
          -
          3. -
        -
        4. -
      -
      2. -
    -
    9. -
  9. If pendingException is not undefined, then return pendingException.
    10. -
  10. Return the result of calling the [[PreventExtensions]] internal method of O.
    11. -
-
- -
-

7.3.12 - TestIntegrityLevel (O, level)

- -

The abstract operation TestIntegrityLevel is used to determine if the - set of own properties of an object are fixed. This abstract operation performs the following steps:

- -
    -
  1. Assert: Type(O) is - Object.
    2. -
  2. Assert: level is either "sealed" or - "frozen".
    3. -
  3. Let status be IsExtensible(O).
    4. -
  4. ReturnIfAbrupt(status).
    5. -
  5. If status is true, then return false
    6. -
  6. NOTE If the object is extensible, none of its properties are examined.
    7. -
  7. Let keysArray be the result of calling the [[OwnPropertyKeys]] internal method of O.
    8. -
  8. Let keys be CreateListFromArrayLike(keysArray).
    9. -
  9. ReturnIfAbrupt(keys).
    10. -
  10. Let pendingException be undefined.
    11. -
  11. Let configurable be false.
    12. -
  12. Let writable be false.
    13. -
  13. Repeat for each element k of keys, -
      -
    1. Let status be the result of calling the [[GetOwnProperty]] internal method of O with k.
      2. -
    2. If status is an abrupt completion, then -
        -
      1. If pendingException is undefined, then set pendingException to status.
        2. -
      2. Let configurable be true.
        3. -
      -
      3. -
    3. Else, -
        -
      1. Let currentDesc be status.[[value]].
        2. -
      2. If currentDesc is not undefined, then -
          -
        1. Set configurable to configurable logically ored with - currentDesc.[[Configurable]].
          2. -
        2. If IsDataDescriptor(currentDesc) is true, then -
            -
          1. Set writable to writable logically ored with currentDesc.[[Writable]].
            2. -
          -
          3. -
        -
        3. -
      -
      4. -
    -
    14. -
  14. If pendingException is not undefined, then return pendingException.
    15. -
  15. If level is "frozen" and writable is true, then return false.
    16. -
  16. If configurable is true, then return false.
    17. -
  17. Return true.
    18. -
-
- -
-

7.3.13 - CreateArrayFromList (elements)

- -

The abstract operation CreateArrayFromList is used to create an Array - object whose elements are provided by a List. This abstract operation - performs the following steps:

- -
    -
  1. Assert: elements is a List whose elements are all ECMAScript language values.
    2. -
  2. Let array be ArrayCreate(0) (see 9.4.2.2).
    3. -
  3. Let n be 0.
    4. -
  4. For each element e of elements -
      -
    1. Let status be the result of CreateDataProperty(array, ToString(n), e).
      2. -
    2. Assert: status is true.
      3. -
    3. Increment n by 1.
      4. -
    -
    5. -
  5. Return array.
    6. -
-
- -
-

7.3.14 CreateListFromArrayLike (obj)

- -

The abstract operation CreateListFromArrayLike is used to create a List value whose elements are provided by the indexed properties of an - array-like object. This abstract operation performs the following steps:

- -
    -
  1. ReturnIfAbrupt(obj).
    2. -
  2. If Type(obj) is not Object, then throw a TypeError - exception.
    3. -
  3. Let len be Get(obj, "length").
    4. -
  4. Let n be ToLength(len).
    5. -
  5. ReturnIfAbrupt(n).
    6. -
  6. Let list be an empty List.
    7. -
  7. Let index be 0.
    8. -
  8. Repeat while index < n -
      -
    1. Let indexName be ToString(index).
      2. -
    2. Let next be Get(obj, indexName).
      3. -
    3. ReturnIfAbrupt(next).
      4. -
    4. Append next as the last element of list.
      5. -
    5. Set index to index + 1.
      6. -
    -
    9. -
  9. Return list.
    10. -
-
- -
-

7.3.15 - OrdinaryHasInstance (C, O)

- -

The abstract operation OrdinaryHasInstance implements the default - algorithm for determining if an object O inherits from the instance object inheritance path provided by - constructor C. This abstract operation performs the following steps:

- -
    -
  1. If IsCallable(C) is false, return false.
    2. -
  2. If C has a [[BoundTargetFunction]] internal slot, then -
      -
    1. Let BC be the value of C’s [[BoundTargetFunction]] internal slot.
      2. -
    2. Return InstanceofOperator(O,BC) (see 12.9.4).
      3. -
    -
    3. -
  3. If Type(O) is not Object, return false.
    4. -
  4. Let P be Get(C, "prototype").
    5. -
  5. ReturnIfAbrupt(P).
    6. -
  6. If Type(P) is not Object, throw a TypeError - exception.
    7. -
  7. Repeat -
      -
    1. Set O to the result of calling the [[GetPrototypeOf]] internal method of O with no arguments.
      2. -
    2. ReturnIfAbrupt(O).
      3. -
    3. If O is null, return false.
      4. -
    4. If SameValue(P, O) is true, return true.
      5. -
    -
    8. -
-
- -
-

7.3.16 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto )

- -

The abstract operation GetPrototypeFromConstructor determines the - [[Prototype]] value that should be used to create an object corresponding to a specific constructor. The value is retrieved - from the constructor’s prototype property, if it exists. Otherwise the supplied default is used for - [[Prototype]]. This abstract operation performs the following steps:

- -
    -
  1. Assert: intrinsicDefaultProto is a string value that is this - specification’s name of an intrinsic object. The corresponding object must be an intrinsic that is intended to - be used as the [[Prototype]] value of an object.
    2. -
  2. If IsConstructor (constructor) is false, then throw a TypeError - exception.
    3. -
  3. Let proto be Get(constructor, "prototype").
    4. -
  4. ReturnIfAbrupt(proto).
    5. -
  5. If Type(proto) is not Object, then -
      -
    1. If constructor has a [[Realm]] internal slot, - let realm be constructor’s [[Realm]] internal slot.
      2. -
    2. Else, -
        -
      1. Let ctx be the running execution context.
        2. -
      2. Let realm be ctx’s Realm.
        3. -
      -
      3. -
    3. Let proto be realm’s intrinsic object named intrinsicDefaultProto.
      4. -
    -
    6. -
  6. Return proto.
    7. -
- -
-

NOTE If constructor does not supply a [[Prototype]] value, the default value that is - used is obtained from the Code Realm of the constructor function rather than from the running execution context. This accounts for the possibility that a built-in - @@create method from a different Code Realm might be installed on constructor.

-
-
- -
-

7.3.17 - CreateFromConstructor (F)

- -

When the abstract operation CreateFromConstructor is called with Object F the following steps are taken:

- -
    -
  1. Let creator be GetMethod (F, @@create).
    2. -
  2. ReturnIfAbrupt(creator).
    3. -
  3. If creator is undefined, then return undefined.
    4. -
  4. Let obj be the result of calling the [[Call]] internal method of creator with arguments F and an - empty List.
    5. -
  5. ReturnIfAbrupt(obj).
    6. -
  6. If Type(obj) is not Object, then throw a TypeError - exception.
    7. -
  7. Return obj.
    8. -
- -
-

NOTE This operation is equivalent to: F[Symbol.create]()followed by an error check.

-
-
- -
-

7.3.18 Construct (F, argumentsList)

- -

When the abstract operation Construct is called with Object F and List argumentsList the following steps are taken:

- -
    -
  1. Assert: Type(F) is - Object.
    2. -
  2. Let obj be CreateFromConstructor(F).
    3. -
  3. ReturnIfAbrupt(obj).
    4. -
  4. If obj is undefined, then -
      -
    1. Let obj be OrdinaryCreateFromConstructor(F, - "%ObjectPrototype%").
      2. -
    2. ReturnIfAbrupt(obj).
      3. -
    3. Assert: Type(obj) is Object.
      4. -
    -
    5. -
  5. Let result be the result of calling the [[Call]] internal method of F, providing obj and - argumentsList as the arguments.
    6. -
  6. ReturnIfAbrupt(result).
    7. -
  7. If Type(result) is Object then return result.
    8. -
  8. Return obj.
    9. -
- -
-

NOTE This operation is equivalent to: new F(...argumentsList)

-
-
- -
-

7.3.19 GetOption - (options, P)

- -

The abstract operation GetOption is used to retrieve the value of a - specific property of an object in situation where the object may not be present. The operation is called with arguments - options and P where options is the object and P is the property key. This abstract operation performs the following steps:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. If options is undefined, then return undefined.
    3. -
  3. If Type(options) is not Object, then throw a - TypeError exception.
    4. -
  4. Return the result of calling the [[Get]] internal method of options passing P and options as the - arguments.
    5. -
-
-
- -
-
-

7.4 Operations on Iterator Objects

- -

See Commmon Iteration Interfaces (25.1).

-
- -
-

7.4.1 - CheckIterable ( obj )

- -

The abstract operation CheckIterable with argument obj performs the following steps:

- -
    -
  1. If Type(obj) is not Object, then return - undefined.
    2. -
  2. Let iteratorGetter be Get(obj, @@iterator).
    3. -
  3. Return iteratorGetter.
    4. -
-
- -
-

7.4.2 GetIterator - ( obj, method )

- -

The abstract operation GetIterator with argument obj and - optional argument method performs the following steps:

- -
    -
  1. If method was not passed, then -
      -
    1. Let method be CheckIterable(obj).
      2. -
    2. ReturnIfAbrupt(method).
      3. -
    -
    2. -
  2. If IsCallable(method) is false, then throw a TypeError - exception.
    3. -
  3. Let iterator be the result of calling the [[Call]] internal method of method with obj as - thisArgument and an empty List as - argumentsList.
    4. -
  4. ReturnIfAbrupt(iterator).
    5. -
  5. If Type(iterator) is not Object, then throw a - TypeError exception.
    6. -
  6. Return iterator.
    7. -
-
- -
-

7.4.3 - IteratorNext ( iterator, value )

- -

The abstract operation IteratorNext with argument iterator and optional argument value performs the - following steps:

- -
    -
  1. If value was not passed, -
      -
    1. Let result be Invoke(iterator, "next", ( )).
      2. -
    -
    2. -
  2. Else, -
      -
    1. Let result be Invoke(iterator, "next", (value)).
      2. -
    -
    3. -
  3. ReturnIfAbrupt(result).
    4. -
  4. If Type(result) is not Object, then throw a - TypeError exception.
    5. -
  5. Return result.
    6. -
-
- -
-

7.4.4 - IteratorComplete ( iterResult )

- -

The abstract operation IteratorComplete with argument iterResult performs the following steps:

- -
    -
  1. Assert: Type(iterResult) is Object.
    2. -
  2. Let done be Get(iterResult, "done").
    3. -
  3. Return ToBoolean(done).
    4. -
-
- -
-

7.4.5 - IteratorValue ( iterResult )

- -

The abstract operation IteratorValue with argument iterResult performs the following steps:

- -
    -
  1. Assert: Type(iterResult) is Object.
    2. -
  2. Return Get(iterResult, "value").
    3. -
-
- -
-

7.4.6 - IteratorStep ( iterator )

- -

The abstract operation IteratorStep with argument iterator requests the next value from iterator - and returns either false indicating that the iterator has reached its end or the IteratorResult - object if a next value is available. IteratorStep performs the following steps:

- -
    -
  1. Let result be IteratorNext(iterator).
    2. -
  2. ReturnIfAbrupt(result).
    3. -
  3. Let done be IteratorComplete(result).
    4. -
  4. ReturnIfAbrupt(done).
    5. -
  5. If done is true, then return false.
    6. -
  6. Return result.
    7. -
-
- -
-

7.4.7 - CreateIterResultObject (value, done)

- -

The abstract operation CreateIterResultObject with arguments value and done creates an object that - supports the IteratorResult interface by performing the following steps:

- -
    -
  1. Assert: Type(done) - is Boolean.
    2. -
  2. Let obj be ObjectCreate(%ObjectPrototype%).
    3. -
  3. Perform CreateDataProperty(obj, "value", value).
    4. -
  4. Perform CreateDataProperty(obj, "done", done).
    5. -
  5. Return obj.
    6. -
-
- -
-
-

7.4.8 - CreateListIterator (list)

- -

The abstract operation CreateListIterator with argument list creates an Iterator (25.1.2) object whose next method returns the successive elements of list. It - performs the following steps:

- -
    -
  1. Let iterator be ObjectCreate(%ObjectPrototype%, ([[IteratedList]], - [[ListIteratorNextIndex]])).
    2. -
  2. Set iterator’s [[IteratedList]] internal - slot to list.
    3. -
  3. Set iterator’s [[ListIteratorNextIndex]] internal slot to 0.
    4. -
  4. Define ListIterator next (7.4.8.1) as an own property of - iterator.
    5. -
  5. Return iterator.
    6. -
-
- -
-

7.4.8.1 - ListIterator next( )

- -

The ListIterator next method is a standard built-in function object (clause 17) that performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If O does not have a [[IteratedList]] internal - slot, then throw a TypeError exception.
    3. -
  3. Let list be the value of the [[IteratedList]] internal slot of O.
    4. -
  4. Let index be the value of the [[ListIteratorNextIndex]] internal slot of O.
    5. -
  5. Let len be the number of elements of list.
    6. -
  6. If index ≥ len, then -
      -
    1. Return CreateIterResultObject(undefined, true).
      2. -
    -
    7. -
  7. Set the value of the [[ListIteratorNextIndex]] internal - slot of O to index+1.
    8. -
  8. Return CreateIterResultObject(list[index], - false).
    9. -
-
-
- -
-

7.4.9 - CreateEmptyIterator ( )

- -

The abstract operation CreateEmptyIterator with no arguments creates an Iterator object whose next method always reports - that the iterator is done. It performs the following steps:

- -
    -
  1. Let empty be a List with no elements.
    2. -
  2. Return CreateListIterator(empty).
    3. -
-
- -
-
-

7.4.10 CreateCompoundIterator ( iterator1, iterator2 )

- -

The abstract operation CreateCompoundIterator with arguments iterator1 and iterator2 creates an - Iterator (25.1.2) object whose next method returns the successive elements of - iterator1 followed by the successive elements of iterator2. It performs the following steps:

- -
    -
  1. Let iterator be ObjectCreate(%ObjectPrototype%, ([[Iterator1]], - [[Iterator2]], [[State]])).
    2. -
  2. Set iterator’s [[Iterator1]] internal - slot to iterator1.
    3. -
  3. Set iterator’s [[Iterator2]] internal - slot to iterator2.
    4. -
  4. Set iterator’s [[State]] internal slot to - 1.
    5. -
  5. Define CompundIterator next (7.4.10.1) as an own property of - iterator.
    6. -
  6. Return iterator.
    7. -
-
- -
-

7.4.10.1 CompoundIterator next( )

- -

The CompoundIterator next method is a standard built-in function object that performs the following - steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If O does not have a [[Iterator1]] internal - slot, then throw a TypeError exception.
    3. -
  3. Assert: O is an object created and initialized by CreateCompoundIterator.
    4. -
  4. Let state be the value of O’s [[State] internal slot.
    5. -
  5. If state = 1, then -
      -
    1. Let iterator1 be the value of O’s [[Iterator1] internal slot.
      2. -
    2. Let result1 be IteratorStep(iterator1).
      3. -
    3. If result1 is not false, then, -
        -
      1. Return result1.
        2. -
      -
      4. -
    4. Set O’s [[State] internal slot to - 2.
      5. -
    -
    6. -
  6. Let iterator2 be the value of O’s [[Iterator2] internal slot.
    7. -
  7. Return IteratorNext(iterator2).
    8. -
-
-
-
- -
-
-

7.5 Operations on Promise Objects

- -

Promise Objects (25.4) serve as a placeholder for the eventual result of a deferred - (and possibly asynchronous) computation.

- -

Within this specification the adjective “eventual” mean a value or a Promise object that will ultimately - resolves to the value. For example, “Returns an eventual String” is equivalent to “Returns either a - String or a Promise object that will eventually resolves to a String”. A “resolved value” is the final - value of an “eventual value”.

- -
-

NOTE The Promise related abstract operations defined in this subclause are used by - specification algorithms when they perform or respond to asynchronous operations. They ensure that the actual built-in - Promise operations are used by the algorithms, even if ECMAScript code has modified the properties of %Promise% or - %PromisePrototype%.

-
-
- -
-

7.5.1 PromiseNew ( - executor ) Abstract Operation

- -

The abstract operation PromiseNew allocates and initializes a new promise object for use by specification - algorithm. The executor argument initiates the deferred computation.

- -
    -
  1. Let promise be AllocatePromise(%Promise%).
    2. -
  2. Return InitializePromise(promise, executor).
    3. -
-
- -
-

7.5.2 PromiseBuiltinCapability () Abstract Operation

- -

The abstract operation PromiseBuiltinCapability allocates a PromiseCapability record (25.4.1.1) for a builtin promise object for use by specification - algorithm.

- -
    -
  1. Let promise be AllocatePromise(%Promise%).
    2. -
  2. Return CreatePromiseCapabilityRecord(promise, %Promise%).
    3. -
- -
-

NOTE This abstract operation is the same as the default built-in behaviour of NewPromiseCapability abstract operation (25.4.1.5).

-
-
- -
-

7.5.3 PromiseOf - (value) Abstract Operation

- -

The abstract operation PromiseOf returns a new Promise that resolves to the argument value.

- -
    -
  1. Assert: IsPromise(value) is - false.
    2. -
  2. Let capability be PromiseBuiltinCapability( ).
    3. -
  3. ReturnIfAbrupt(capability).
    4. -
  4. Let resolveResult be the result of calling the [[Call]] internal method of capability.[[Resolve]] with - undefined as thisArgument and (value) as argumentsList.
    5. -
  5. ReturnIfAbrupt(resolveResult).
    6. -
  6. Return capability.[[Promise]].
    7. -
- -
-

NOTE This abstract operation is the same as the default built-in behaviour of the Promise.resolve method (25.4.4.5). However, PromiseOf - does not accept a Promise is its argument.

-
-
- -
-

7.5.4 PromiseAll - (promiseList) Abstract Operation

-
- -
-

7.5.5 - PromiseCatch (promise, rejectedAction) Abstract Operation

-
- -
-

7.5.6 PromiseThen - (promise, resolvedAction, rejectedAction) Abstract Operation

-
-
-
- -
-
-

8 Executable Code and Execution Contexts

-
- -
-
-

8.1 - Lexical Environments

- -

A Lexical Environment is a specification type used to define the association of Identifiers to specific variables and functions based upon the lexical nesting structure of ECMAScript - code. A Lexical Environment consists of an Environment Record and a possibly null - reference to an outer Lexical Environment. Usually a Lexical Environment is associated with some specific syntactic - structure of ECMAScript code such as a FunctionDeclaration, a BlockStatement, or a Catch clause of a TryStatement and a - new Lexical Environment is created each time such code is evaluated.

- -

An Environment Record records the identifier bindings that are created - within the scope of its associated Lexical Environment.

- -

The outer environment reference is used to model the logical nesting of Lexical Environment values. The outer reference - of a (inner) Lexical Environment is a reference to the Lexical Environment that logically surrounds the inner Lexical - Environment. An outer Lexical Environment may, of course, have its own outer Lexical Environment. A Lexical Environment may - serve as the outer environment for multiple inner Lexical Environments. For example, if a FunctionDeclaration contains two nested FunctionDeclarations then the Lexical - Environments of each of the nested functions will have as their outer Lexical Environment the Lexical Environment of the - current evaluation of the surrounding function.

- -

A global environment is a Lexical Environment which does not have an outer environment. The global - environment’s outer environment reference is null. A global environment’s environment record may be - prepopulated with identifier bindings and includes an associated global object whose properties provide some of the global environment’s identifier bindings. This global object is the - value of a global environment’s this binding. As ECMAScript code is executed, additional properties may - be added to the global object and the initial properties may be modified.

- -

A method environment is a Lexical Environment that corresponds to the invocation of an ECMAScript function object that establishes a new this binding. A - method environment also captures the state necessary to support super method invocations.

- -

Lexical Environments and Environment Record values are purely specification - mechanisms and need not correspond to any specific artefact of an ECMAScript implementation. It is impossible for an - ECMAScript program to directly access or manipulate such values.

-
- -
-
-

8.1.1 - Environment Records

- -

There are two primary kinds of Environment Record values used in this specification: declarative environment - records and object environment records. Declarative environment records are used to define the effect of - ECMAScript language syntactic elements such as FunctionDeclarations, VariableDeclarations, and Catch clauses that directly associate identifier - bindings with ECMAScript language values. Object environment records are used - to define the effect of ECMAScript elements such as WithStatement that associate identifier - bindings with the properties of some object. Global Environment Records and - Function Environment Records are specializations that are used for - specifically for Script global declarations and for top-level declarations within functions.

- -

For specification purposes Environment Record values can be thought of as existing in a simple object-oriented - hierarchy where Environment Record is an abstract class with three concrete subclasses, declarative environment record, object environment record, and global - environment record. Function environment records are a subclass of declarative environment record. The abstract class includes the abstract - specification methods defined in Table 16. These abstract methods have distinct concrete - algorithms for each of the concrete subclasses.

- -
-
Table 16 — Abstract Methods of Environment Records
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
MethodPurpose
HasBinding(N)Determine if an environment record has a binding for an identifier. Return true if it does and false if it does not. The String value N is the text of the identifier.
CreateMutableBinding(N, D)Create a new but uninitialized mutable binding in an environment record. The String value N is the text of the bound name. If the optional Boolean argument D is true the binding is may be subsequently deleted.
CreateImmutableBinding(N)Create a new but uninitialized immutable binding in an environment record. The String value N is the text of the bound name.
InitializeBinding(N,V)Set the value of an already existing but uninitialized binding in an environment record. The String value N is the text of the bound name. V is the value for the binding and is a value of any ECMAScript language type.
SetMutableBinding(N,V, S)Set the value of an already existing mutable binding in an environment record. The String value N is the text of the bound name. V is the value for the binding and may be a value of any ECMAScript language type. S is a Boolean flag. If S is true and the binding cannot be set throw a TypeError exception. S is used to identify strict mode references.
GetBindingValue(N,S)Returns the value of an already existing binding from an environment record. The String value N is the text of the bound name. S is used to identify strict mode references. If S is true and the binding does not exist throw a ReferenceError exception. If the binding exists but is uninitialized a ReferenceError is thrown, regardless of the value of S.
DeleteBinding(N)Delete a binding from an environment record. The String value N is the text of the bound name If a binding for N exists, remove the binding and return true. If the binding exists but cannot be removed return false. If the binding does not exist return true.
HasThisBinding()Determine if an environment record establishes a this binding. Return true if it does and false if it does not.
HasSuperBinding()Determine if an environment record establishes a super method binding. Return true if it does and false if it does not.
WithBaseObject ()If this environment record is associated with a with statement, return the with object. Otherwise, return undefined.
-
-
- -
-
-

8.1.1.1 Declarative Environment Records

- -

Each declarative environment record is associated with an ECMAScript program scope containing variable, constant, - let, class, module, import, and/or function declarations. A declarative environment record binds the set of identifiers - defined by the declarations contained within its scope.

- -

The behaviour of the concrete specification methods for Declarative Environment Records is defined by the following - algorithms.

-
- -
-

8.1.1.1.1 HasBinding(N)

- -

The concrete environment record method HasBinding for declarative environment records simply determines if the - argument identifier is one of the identifiers bound by the record:

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. If envRec has a binding for the name that is the value of N, return true.
    3. -
  3. Return false.
    4. -
-
- -
-

8.1.1.1.2 CreateMutableBinding (N, D)

- -

The concrete Environment Record method CreateMutableBinding for declarative - environment records creates a new mutable binding for the name N that is uninitialized. A binding must not - already exist in this Environment Record for N. If Boolean argument - D is provided and has the value true the new binding is marked as being subject to deletion.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. Assert: envRec does not already have a binding for N.
    3. -
  3. Create a mutable binding in envRec for N and record that it is uninitialized. If D is - true record that the newly created binding may be deleted by a subsequent DeleteBinding call.
    4. -
  4. Return NormalCompletion(empty).
    5. -
-
- -
-

8.1.1.1.3 CreateImmutableBinding (N)

- -

The concrete Environment Record method CreateImmutableBinding for declarative - environment records creates a new immutable binding for the name N that is uninitialized. A binding must not - already exist in this environment record for N.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. Assert: envRec does not already have a binding for N.
    3. -
  3. Create an immutable binding in envRec for N and record that it is uninitialized.
    4. -
-
- -
-

8.1.1.1.4 InitializeBinding (N,V)

- -

The concrete Environment Record method InitializeBinding for declarative - environment records is used to set the bound value of the current binding of the identifier whose name is the value of - the argument N to the value of argument V. An uninitialized binding for N must already - exist.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. Assert: envRec must have an uninitialized binding for - N.
    3. -
  3. Set the bound value for N in envRec to V.
    4. -
  4. Record that the binding for N in envRec has been initialized.
    5. -
-
- -
-

8.1.1.1.5 SetMutableBinding (N,V,S)

- -

The concrete Environment Record method SetMutableBinding for declarative - environment records attempts to change the bound value of the current binding of the identifier whose name is the value - of the argument N to the value of argument V. A binding for N must already exist. If - the binding is an immutable binding, a TypeError is thrown if S - is true.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. Assert: envRec must have a binding for N.
    3. -
  3. If the binding for N in envRec has not yet been initialized throw a ReferenceError - exception.
    4. -
  4. Else if the binding for N in envRec is a mutable binding, change its bound value to V.
    5. -
  5. Else this must be an attempt to change the value of an immutable binding so if S is true throw a - TypeError exception.
    6. -
  6. Return NormalCompletion(empty).
    7. -
-
- -
-

8.1.1.1.6 GetBindingValue(N,S)

- -

The concrete Environment Record method GetBindingValue for declarative - environment records simply returns the value of its bound identifier whose name is the value of the argument - N. If the binding exists but is uninitialized a ReferenceError is thrown, regardless of the value of - S.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. Assert: envRec has a binding for N.
    3. -
  3. If the binding for N in envRec is an uninitialized binding, then throw a ReferenceError - exception.
    4. -
  4. Return the value currently bound to N in envRec.
    5. -
-
- -
-

8.1.1.1.7 DeleteBinding (N)

- -

The concrete Environment Record method DeleteBinding for declarative - environment records can only delete bindings that have been explicitly designated as being subject to deletion.

- -
    -
  1. Let envRec be the declarative environment record for - which the method was invoked.
    2. -
  2. If envRec does not have a binding for the name that is the value of N, return true.
    3. -
  3. If the binding for N in envRec cannot be deleted, return false.
    4. -
  4. Remove the binding for N from envRec.
    5. -
  5. Return true.
    6. -
-
- -
-

8.1.1.1.8 HasThisBinding ()

- -

Regular Declarative Environment Records do not provide a this binding.

- -
    -
  1. Return false.
    2. -
-
- -
-

8.1.1.1.9 HasSuperBinding ()

- -

Regular Declarative Environment Records do not provide a super binding.

- -
    -
  1. Return false.
    2. -
-
- -
-

8.1.1.1.10 WithBaseObject()

- -

Declarative Environment Records always return undefined as their WithBaseObject.

- -
    -
  1. Return undefined.
    2. -
-
-
- -
-
-

8.1.1.2 Object Environment Records

- -

Each object environment record is associated with an object called its binding object. An object environment - record binds the set of string identifier names that directly correspond to the property names of its binding object. - Property keys that are not strings in the form of an IdentifierName are not included in the set - of bound identifiers. Both own and inherited properties are included in the set regardless of the setting of their - [[Enumerable]] attribute. Because properties can be dynamically added and deleted from objects, the set of identifiers - bound by an object environment record may potentially change as a side-effect of any operation that adds or deletes - properties. Any bindings that are created as a result of such a side-effect are considered to be a mutable binding even - if the Writable attribute of the corresponding property has the value false. Immutable bindings do not exist for - object environment records.

- -

Object environment records also have a possibly empty List of - strings called unscopables. The strings in this List - are excluded from the environment records set of bound names, regardless of whether or not they exist as property keys - of its binding object.

- -

Object environment records created for with statements (13.10) can - provide their binding object as an implicit this value for use in function calls. The capability is controlled by a - withEnvironment Boolean value that is associated with each object environment record. By default, the value - of withEnvironment is false for any object environment record.

- -

The behaviour of the concrete specification methods for Object Environment Records is defined by the following - algorithms.

-
- -
-

8.1.1.2.1 HasBinding(N)

- -

The concrete Environment Record method HasBinding for object environment - records determines if its associated binding object has a property whose name is the value of the argument - N:

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. If N is an element of envRec’s unscopables, then return false.
    3. -
  3. Let bindings be the binding object for envRec.
    4. -
  4. Return the result of HasProperty(bindings, N).
    5. -
-
- -
-

8.1.1.2.2 CreateMutableBinding (N, D)

- -

The concrete Environment Record method CreateMutableBinding for object - environment records creates in an environment record’s associated binding object a property whose name is the - String value and initializes it to the value undefined. If Boolean argument D is provided and has the - value true the new property’s [[Configurable]] attribute is set to true, otherwise it is set to - false.

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. Let bindings be the binding object for envRec.
    3. -
  3. If D is true then let configValue be true otherwise let configValue be - false.
    4. -
  4. Return DefinePropertyOrThrow(bindings, N, - PropertyDescriptor{[[Value]]:undefined, [[Writable]]: true, [[Enumerable]]: true , - [[Configurable]]: configValue}).
    5. -
- -
-

NOTE Normally envRec will not have a binding for N but if it does, the - semantics of DefinePropertyOrThrow may result in an existing binding being - replaced or shadowed or cause an abrupt completion to be - returned.

-
-
- -
-

8.1.1.2.3 CreateImmutableBinding (N)

- -

The concrete Environment Record method CreateImmutableBinding is never used - within this specification in association with Object environment records.

-
- -
-

8.1.1.2.4 InitializeBinding (N,V)

- -

The concrete Environment Record method InitializeBinding for object - environment records is used to set the bound value of the current binding of the identifier whose name is the value of - the argument N to the value of argument V. An uninitialized binding for N must already - exist.

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. Assert: envRec must have an uninitialized binding for - N.
    3. -
  3. Record that the binding for N in envRec has been initialized.
    4. -
  4. Return the result of calling the SetMutableBinding concrete method of envRec with N, V, and - false as arguments.
    5. -
-
- -
-

8.1.1.2.5 SetMutableBinding (N,V,S)

- -

The concrete Environment Record method SetMutableBinding for object - environment records attempts to set the value of the environment record’s associated binding object’s - property whose name is the value of the argument N to the value of argument V. A property named - N normally already exists but if it does not or is not currently writable, error handling is determined by - the value of the Boolean argument S.

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. Let bindings be the binding object for envRec.
    3. -
  3. Return Put(bindings, N, V, and S).
    4. -
-
- -
-

8.1.1.2.6 GetBindingValue(N,S)

- -

The concrete Environment Record method GetBindingValue for object environment - records returns the value of its associated binding object’s property whose name is the String value of the - argument identifier N. The property should already exist but if it does not the result depends upon the value - of the S argument:

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. Let bindings be the binding object for envRec.
    3. -
  3. Let value be HasProperty(bindings, N).
    4. -
  4. ReturnIfAbrupt(value).
    5. -
  5. If value is false, then -
      -
    1. If S is false, return the value undefined, otherwise throw a ReferenceError - exception.
      2. -
    -
    6. -
  6. Return Get(bindings, N).
    7. -
-
- -
-

8.1.1.2.7 DeleteBinding (N)

- -

The concrete Environment Record method DeleteBinding for object environment - records can only delete bindings that correspond to properties of the environment object whose [[Configurable]] - attribute have the value true.

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. Let bindings be the binding object for envRec.
    3. -
  3. Return the result of calling the [[Delete]] internal method of bindings passing N as the - argument.
    4. -
-
- -
-

8.1.1.2.8 HasThisBinding ()

- -

Regular Object Environment Records do not provide a this binding.

- -
    -
  1. Return false.
    2. -
-
- -
-

8.1.1.2.9 HasSuperBinding ()

- -

Regular Object Environment Records do not provide a super binding.

- -
    -
  1. Return false.
    2. -
-
- -
-

8.1.1.2.10 WithBaseObject()

- -

Object Environment Records return undefined as their WithBaseObject unless their withEnvironment - flag is true.

- -
    -
  1. Let envRec be the object environment record for which the - method was invoked.
    2. -
  2. If the withEnvironment flag of envRec is true, return the binding object for - envRec.
    3. -
  3. Otherwise, return undefined.
    4. -
-
-
- -
-
-

8.1.1.3 Function Environment Records

- -

A function environment record is a declarative environment record - that is used to represent the outer most scope of a function that provides a this binding. In addition to - its identifier bindings, a function environment record contains the this value used within its scope. If such a - function references super, its function environment record also contains the state that is used to perform - super method invocations from within the function.

- -

Function environment records store their this binding as the value of their thisValue. If the - associated function references super, the environment record stores in HomeObject - the object that the function is bound to as a method and in MethodName the property key used for unqualified super invocations from within the function. The default - value for HomeObject and MethodName is undefined.

- -

Methods environment records support all of Declarative Environment - Record methods listed in Table 16 and share the same specifications for all of those methods - except for HasThisBinding and HasSuperBinding. In addition, declarative environment records support the methods listed - in Table 17:

- -
-
Table 17 — Additional Methods of Function Environment Records
- - - - - - - - - - - - - - - - - -
MethodPurpose
GetThisBinding()Return the value of this environment record’s this binding.
GetSuperBase()Return the object that is the base for super property accesses bound in this environment record. The object is derived from this environment record’s HomeObject binding. If the value is Empty, return undefined.
GetMethodName()Return the value of this environment record’s MethodName binding.
-
- -

The behaviour of the additional concrete specification methods for Function Environment Records is defined by the - following algorithms:

-
- -
-

8.1.1.3.1 HasThisBinding ()

- -

Function Environment Records always provide a this - binding.

- -
    -
  1. Return true.
    2. -
-
- -
-

8.1.1.3.2 HasSuperBinding ()

-
    -
  1. If this environment record’s HomeObject has the value Empty, then return false. Otherwise, return true.
    2. -
-
- -
-

8.1.1.3.3 GetThisBinding ()

-
    -
  1. Return the value of this environment record’s thisValue.
    2. -
-
- -
-

8.1.1.3.4 GetSuperBase ()

-
    -
  1. Let home be the value of this environment record’s HomeObject.
    2. -
  2. If home has the value Empty, then return - undefined.
    3. -
  3. Assert: Type(home) is Object.
    4. -
  4. Return the result of calling home’s [[GetPrototypeOf]] internal method.
    5. -
-
- -
-

8.1.1.3.5 GetMethodName ()

-
    -
  1. Return the value of this environment record’s MethodName.
    2. -
-
-
- -
-
-

8.1.1.4 Global Environment Records

- -

A global environment record is used to represent the outer most scope that is shared by all of the ECMAScript Script elements that are processed in a common Realm (8.1.2.5). A global environment record provides the bindings for built-in globals - (clause 18), properties of the global object, and for all declarations that are not - function code and that occur within Script productions.

- -

A global environment record is logically a single record but it is specified as a composite encapsulating an object environment record and a declarative environment record. The object environment record has as its base object the global object of the - associated Realm. This global object is also the value of the global environment - record’s thisValue. The object environment record - component of a global environment record contains the bindings for all built-in globals (clause 18) and all bindings introduced by a FunctionDeclaration, GeneratorDeclaration, or VariableStatement - contained in global code. The bindings for all other ECMAScript declarations in global code are contained in the declarative environment record component of the global environment - record.

- -

Properties may be created directly on a global object. Hence, the object - environment record component of a global environment record may contain both bindings created explicitly by FunctionDeclaration, GeneratorDeclaration, or VariableDeclaration declarations and binding created implicitly as properties of the global object. In - order to identify which bindings were explicitly created using declarations, a global environment record maintains a - list of the names bound using its CreateGlobalVarBindings and CreateGlobalFunctionBindings concrete methods.

- -

Global environment records have the additional state components listed in Table 18 and the - additional methods listed in Table 19.

- -
-
Table 18 — Components of Global Environment Records
- - - - - - - - - - - - - - - - - -
ComponentPurpose
ObjectRecordAn Object Environment Record whose base object is the global object. It contains global built-in bindings as well as FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration bindings in global code for the associated Realm.
DeclarativeRecordA Declarative Environment Record that contains bindings for all declarations in global code for the associated Realm code except for FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration bindings.
VarNamesA List containing the string names bound by FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration declarations in global code for the associated Realm.
-
- -
-
Table 19 — Additional Methods of Global Environment Records
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
MethodPurpose
GetThisBinding()Return the value of this environment record’s this binding.
HasVarDeclaration (N)Determines if the argument identifier has a binding in this environment record that was created using a VariableDeclaration, FunctionDeclaration, or GeneratorDeclaration.
HasLexicalDeclaration (N)Determines if the argument identifier has a binding in this environment record that was created using a lexical declaration such as a LexicalDeclaration or a ClassDeclaration.
CanDeclareGlobalVar (N)Determines if a corresponding CreateGlobalVarBinding call would succeed if called for the same argument N.
CanDeclareGlobalFunction (N)Determines if a corresponding CreateGlobalFunctionBinding call would succeed if called for the same argument N.
CreateGlobalVarBinding(N, D)Used to create global var bindings in the ObjectRecord component of a global environment record. The binding will be a mutable binding. The corresponding global object property will have attribute values approate for a var. The String value N is the text of the bound name. V is the initial value of the binding If the optional Boolean argument D is true the binding is may be subsequently deleted. This is logically equivalent to CreateMutableBinding but it allows var declarations to receive special treatment.
CreateGlobalFunctionBinding(N, V, D)Used to create and initialize global function bindings in the ObjectRecord component of a global environment record. The binding will be a mutable binding. The corresponding global object property will have attribute values approate for a function.The String value N is the text of the bound name. If the optional Boolean argument D is true the binding is may be subsequently deleted. This is logically equivalent to CreateMutableBinding followed by a SetMutableBinding but it allows function declarations to receive special treatment.
-
- -

The behaviour of the concrete specification methods for Global Environment Records is defined by the following - algorithms.

-
- -
-

8.1.1.4.1 HasBinding(N)

- -

The concrete environment record method HasBinding for global environment records simply determines if the argument - identifier is one of the identifiers bound by the record:

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. If the result of calling DclRec’s HasBinding concrete method with argument N is true, - return true.
    4. -
  4. Let ObjRec be envRec’s ObjectRecord.
    5. -
  5. Return the result of calling ObjRec’s HasBinding concrete method with argument N.
    6. -
-
- -
-

8.1.1.4.2 CreateMutableBinding (N, D)

- -

The concrete environment record method CreateMutableBinding for global environment records creates a new mutable - binding for the name N that is uninitialized. The binding is created in the associated DeclarativeRecord. A - binding for N must not already exist in the DeclarativeRecord. If Boolean argument D is provided - and has the value true the new binding is marked as being subject to deletion.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. Assert: DclRec does not already have a binding for N.
    4. -
  4. Return the result of calling the CreateMutableBinding concrete method of DclRec with arguments N and - D.
    5. -
-
- -
-

8.1.1.4.3 CreateImmutableBinding (N)

- -

The concrete Environment Record method CreateImmutableBinding for global - environment records creates a new immutable binding for the name N that is uninitialized. A binding must not - already exist in this environment record for N.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. Assert: DclRec does not already have a binding for N.
    4. -
  4. Return the result of calling the CreateImmutableBinding concrete method of DclRec with argument - N.
    5. -
-
- -
-

8.1.1.4.4 InitializeBinding (N,V)

- -

The concrete Environment Record method InitializeBinding for global - environment records is used to set the bound value of the current binding of the identifier whose name is the value of - the argument N to the value of argument V. An uninitialized binding for N must already - exist.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. If the result of calling DclRec’s HasBinding concrete method with argument N is true, - then -
      -
    1. Return the result of calling DclRec’s InitializeBinding concrete method with arguments N - and V.
      2. -
    -
    4. -
  4. Assert: If the binding exists it must be in the object environment record.
    5. -
  5. Let ObjRec be envRec’s ObjectRecord.
    6. -
  6. Return the result of calling ObjRec’s InitializeBinding concrete method with arguments N and - V.
    7. -
-
- -
-

8.1.1.4.5 SetMutableBinding (N,V,S)

- -

The concrete Environment Record method SetMutableBinding for global - environment records attempts to change the bound value of the current binding of the identifier whose name is the value - of the argument N to the value of argument V. If the binding is an immutable binding, a - TypeError is thrown if S is true. A - property named N normally already exists but if it does not or is not currently writable, error handling is - determined by the value of the Boolean argument S.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. If the result of calling DclRec’s HasBinding concrete method with argument N is true, - then -
      -
    1. Return the result of calling the SetMutableBinding concrete method of DclRec with arguments N, - V, and S.
      2. -
    -
    4. -
  4. Let ObjRec be envRec’s ObjectRecord.
    5. -
  5. Return the result of calling the SetMutableBinding concrete method of ObjRec with arguments N, - V, and S.
    6. -
-
- -
-

8.1.1.4.6 GetBindingValue(N,S)

- -

The concrete Environment Record method GetBindingValue for global environment - records simply returns the value of its bound identifier whose name is the value of the argument N. If the - binding is an uninitialized binding throw a ReferenceError exception. A property named N normally - already exists but if it does not or is not currently writable, error handling is determined by the value of the Boolean - argument S.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. If the result of calling DclRec’s HasBinding concrete method with argument N is true, - then -
      -
    1. Return the result of calling the GetBindingValue concrete method of DclRec with arguments N and - S.
      2. -
    -
    4. -
  4. Let ObjRec be envRec’s ObjectRecord.
    5. -
  5. Return the result of calling the GetBindingValue concrete method of ObjRec with arguments N, and - S.
    6. -
-
- -
-

8.1.1.4.7 DeleteBinding (N)

- -

The concrete Environment Record method DeleteBinding for global environment - records can only delete bindings that have been explicitly designated as being subject to deletion.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. If the result of calling DclRec’s HasBinding concrete method with argument N is true, - then -
      -
    1. Return the result of calling the DeleteBinding concrete method of DclRec with argument N.
      2. -
    -
    4. -
  4. Let ObjRec be envRec’s ObjectRecord.
    5. -
  5. If the result of calling ObjRec’s HasBinding concrete method with argument N is true, - then -
      -
    1. Let status be the result of calling the DeleteBinding concrete method of ObjRec with argument - N.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    3. If status is true, then -
        -
      1. Let varNames be envRec’s VarNames List.
        2. -
      2. If N is an element of varNames, then remove that element from the varNames.
        3. -
      -
      4. -
    4. Return status.
      5. -
    -
    6. -
  6. Return true.
    7. -
-
- -
-

8.1.1.4.8 HasThisBinding ()

- -

Global Environment Records always provide a this binding - whose value is the associated global object.

- -
    -
  1. Return true.
    2. -
-
- -
-

8.1.1.4.9 HasSuperBinding ()

-
    -
  1. Return false.
    2. -
-
- -
-

8.1.1.4.10 WithBaseObject()

- -

Global Environment Records always return undefined as their - WithBaseObject.

- -
    -
  1. Return undefined.
    2. -
-
- -
-

8.1.1.4.11 GetThisBinding ()

-
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let ObjRec be envRec’s ObjectRecord.
    3. -
  3. Let bindings be the binding object for ObjRec.
    4. -
  4. Return bindings.
    5. -
-
- -
-

8.1.1.4.12 HasVarDeclaration (N)

- -

The concrete environment record method HasVarDeclaration for global environment records determines if the argument - identifier has a binding in this record that was created using a VariableStatement or a FunctionDeclaration :

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let varDeclaredNames be envRec’s VarNames List.
    3. -
  3. If varDeclaredNames contains the value of N, return true.
    4. -
  4. Return false.
    5. -
-
- -
-

8.1.1.4.13 HasLexicalDeclaration (N)

- -

The concrete environment record method HasLexicalDeclaration for global environment records determines if the - argument identifier has a binding in this record that was created using a lexical declaration such as a LexicalDeclaration or a ClassDeclaration :

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let DclRec be envRec’s DeclarativeRecord.
    3. -
  3. Return the result of calling DclRec’s HasBinding concrete method with argument N.
    4. -
-
- -
-

8.1.1.4.14 CanDeclareGlobalVar (N)

- -

The concrete environment record method CanDeclareGlobalVar for global environment records determines if a - corresponding CreateGlobalVarBinding call would succeed if called for the same - argument N. Redundent var declarations and var declarations for pre-existing global object properties are - allowed.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let ObjRec be envRec’s ObjectRecord.
    3. -
  3. If the result of calling ObjRec’s HasBinding concrete method with argument N is true, - return true.
    4. -
  4. Let bindings be the binding object for ObjRec.
    5. -
  5. Let extensible be IsExtensible(bindings).
    6. -
  6. Return extensible.
    7. -
-
- -
-

8.1.1.4.15 CanDeclareGlobalFunction (N)

- -

The concrete environment record method CanDeclareGlobalFunction for global environment records determines if a - corresponding CreateGlobalFunctionBinding call would succeed if called - for the same argument N.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let ObjRec be envRec’s ObjectRecord.
    3. -
  3. Let globalObject be the binding object for ObjRec.
    4. -
  4. Let extensible be IsExtensible(globalObject).
    5. -
  5. ReturnIfAbrupt(extensible).
    6. -
  6. If the result of calling ObjRec’s HasBinding concrete method with argument N is false, - then return extensible.
    7. -
  7. Let existingProp be the result of calling the [[GetOwnProperty]] internal method of globalObject - with argument N.
    8. -
  8. ReturnIfAbrupt(existingProp).
    9. -
  9. If existingProp is undefined, then return extensible.
    10. -
  10. If existingProp.[[Configurable]] is true, then return true.
    11. -
  11. If IsDataDescriptor(existingProp) is true and - existingProp has attribute values {[[Writable]]: true, [[Enumerable]]: true}, then return - true.
    12. -
  12. Return false.
    13. -
-
- -
-

8.1.1.4.16 CreateGlobalVarBinding (N, D)

- -

The concrete Environment Record method CreateGlobalVarBinding for global - environment records creates a mutable binding in the associated object - environment record and records the bound name in the associated VarNames List. If a binding already exists, it is reused.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let ObjRec be envRec’s ObjectRecord.
    3. -
  3. If the result of calling ObjRec’s HasBinding concrete method with argument N is false, - then -
      -
    1. Let status be the result of calling the CreateMutableBinding concrete method of ObjRec with - arguments N and D.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    4. -
  4. Let varDeclaredNames be envRec’s VarNames List.
    5. -
  5. If varDeclaredNames does not contain the value of N, then -
      -
    1. Append N to varDeclaredNames.
      2. -
    -
    6. -
  6. Return NormalCompletion(empty).
    7. -
-
- -
-

8.1.1.4.17 CreateGlobalFunctionBinding (N, V, D)

- -

The concrete Environment Record method CreateGlobalFunctionBinding for global - environment records creates a mutable binding in the associated object - environment record and records the bound name in the associated VarNames List. If a binding already exists, it is replaced.

- -
    -
  1. Let envRec be the global environment record for which the - method was invoked.
    2. -
  2. Let ObjRec be envRec’s ObjectRecord.
    3. -
  3. Let globalObject be the binding object for ObjRec.
    4. -
  4. Let existingProp be the result of calling the [[GetOwnProperty]] internal method of globalObject - with argument N.
    5. -
  5. ReturnIfAbrupt(existingProp).
    6. -
  6. If existingProp is undefined or existingProp.[[Configurable]] is true, then -
      -
    1. Let desc be the PropertyDescriptor{[[Value]]:V, [[Writable]]: true, [[Enumerable]]: - true , [[Configurable]]: D}.
      2. -
    -
    7. -
  7. Else, -
      -
    1. Let desc be the PropertyDescriptor{[[Value]]:V }.
      2. -
    -
    8. -
  8. Let status be DefinePropertyOrThrow(globalObject, N, - desc).
    9. -
  9. ReturnIfAbrupt(status).
    10. -
  10. Let varDeclaredNames be envRec’s VarNames List.
    11. -
  11. If varDeclaredNames does not contain the value of N, then -
      -
    1. Append N to varDeclaredNames.
      2. -
    -
    12. -
  12. Return NormalCompletion(empty).
    13. -
- -
-

NOTE Global function declarations are always represented as own properties of the global - object. If possible, an existing own property is reconfigured to have a standard set of attribute values.

-
-
-
-
- -
-
-

8.1.2 Lexical Environment Operations

- -

The following abstract operations are used in this specification to operate upon lexical environments:

-
- -
-

8.1.2.1 GetIdentifierReference (lex, name, strict) Abstract Operation

- -

The abstract operation GetIdentifierReference is called with a Lexical - Environment lex, a String name, and a Boolean flag strict. The value of - lex may be null. When called, the following steps are performed:

- -
    -
  1. If lex is the value null, then -
      -
    1. Return a value of type Reference whose base value is - undefined, whose referenced name is name, and whose strict reference flag is strict.
      2. -
    -
    2. -
  2. Let envRec be lex’s environment record.
    3. -
  3. Let exists be the result of calling the HasBinding concrete method of envRec passing name as - the argument.
    4. -
  4. ReturnIfAbrupt(exists).
    5. -
  5. If exists is true, then -
      -
    1. Return a value of type Reference whose base value is - envRec, whose referenced name is name, and whose strict reference flag is strict.
      2. -
    -
    6. -
  6. Else -
      -
    1. Let outer be the value of lex’s outer environment - reference.
      2. -
    2. Return GetIdentifierReference(outer, name, strict).
      3. -
    -
    7. -
-
- -
-

8.1.2.2 NewDeclarativeEnvironment (E) Abstract Operation

- -

When the abstract operation NewDeclarativeEnvironment is called with either a Lexical Environment or null as argument E the following steps are - performed:

- -
    -
  1. Let env be a new Lexical Environment.
    2. -
  2. Let envRec be a new declarative environment record - containing no bindings.
    3. -
  3. Set env’s environment record to be envRec.
    4. -
  4. Set the outer lexical environment reference of env to E.
    5. -
  5. Return env.
    6. -
-
- -
-

8.1.2.3 NewObjectEnvironment (O, E) Abstract Operation

- -

When the abstract operation NewObjectEnvironment is called with an Object O and a Lexical Environment E (or null) as arguments, the following steps - are performed:

- -
    -
  1. Let env be a new Lexical Environment.
    2. -
  2. Let envRec be a new object environment record containing - O as the binding object.
    3. -
  3. Set envRec’s unscopables to an empty List.
    4. -
  4. Set env’s environment record to envRec.
    5. -
  5. Set the outer lexical environment reference of env to E.
    6. -
  6. Return env.
    7. -
-
- -
-

8.1.2.4 NewFunctionEnvironment (F, T) Abstract Operation

- -

When the abstract operation NewFunctionEnvironment is called with an ECMAScript function Object F and an - ECMAScript value T as arguments, the following steps are performed:

- -
    -
  1. Assert: The value of F’s [[ThisMode]] internal slot is not lexical.
    2. -
  2. Let env be a new Lexical Environment.
    3. -
  3. Let envRec be a new Function environment record containing - containing no bindings.
    4. -
  4. Set envRec’s thisValue to T.
    5. -
  5. If F’s [[NeedsSuper]] internal slot is - true, then -
      -
    1. Let home be the value of F’s [[HomeObject]] internal slot.
      2. -
    2. If home is undefined, then throw a ReferenceError exception.
      3. -
    3. Set envRec’s HomeObject to home.
      4. -
    4. Set envRec’s MethodName to the value of F’s [[MethodName]] internal slot.
      5. -
    -
    6. -
  6. Else, -
      -
    1. Set envRec’s HomeObject to Empty.
      2. -
    -
    7. -
  7. Set env’s environment record to be envRec.
    8. -
  8. Set the outer lexical environment reference of env to the value of - F’s [[Environment]] internal slot.
    9. -
  9. Return env.
    10. -
-
- -
-

8.1.2.5 NewGlobalEnvironment ( G ) Abstract Operation

- -

When the abstract operation NewGlobalEnvironment is called with an ECMAScript Object G as its argument, the - following steps are performed:

- -
    -
  1. Let env be a new Lexical Environment.
    2. -
  2. Let objRec be a new object environment record containing - G as the binding object.
    3. -
  3. Set objRec’s unscopables to an empty List.
    4. -
  4. Let dclRec be a new declarative environment record - containing no bindings.
    5. -
  5. Let globalRec be a new global environment record.
    6. -
  6. Set globalRec’s ObjectRecord to objRec.
    7. -
  7. Set globalRec’s DeclarativeRecord to dclRec.
    8. -
  8. Set globalRec’s VarNames to a new empty List.
    9. -
  9. Set env’s environment record to globalRec.
    10. -
  10. Set the outer lexical environment reference of env to - null
    11. -
  11. Return env.
    12. -
-
-
-
- -
-
-

8.2 Code - Realms

- -

Before it is evaluated, all ECMAScript code must be associated with a Realm. Conceptually, a realm consists of a - set of intrinsic objects, an ECMAScript global environment, all of the ECMAScript code that is loaded within the scope of - that global environment, a Loader object that can associate new ECMAScript code with the realm, and other associated state - and resources.

- -

A Realm is specified as a Record with the fields specified in Table 20:

- -
-
Table 20 — Realm Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValueMeaning
[[intrinsics]]A record whose field names are intrinsic keys and whose values are objectsThese are the intrinsic values used by code associated with this Realm
[[globalThis]]An objectThe global object for this Realm
[[globalEnv]]An ECMAScript environmentThe global environment for this Realm
[[directEvalTranslate]]undefined or an object that is callable as a function.
[[nonEvalFallback]]undefined or an object that is callable as a function.
[[indirectEval]]undefined or an object that is callable as a function.
[[loader]]any ECMAScript identifier or emptyThe Loader object that can associate ECMAScript code with this Realm
-
-
- -
-

8.2.1 CreateRealm - ( ) Abstract Operation

- -

The abstract operation CreateRealm with no arguments performs the following steps:

- -
    -
  1. Let realmRec be a new Record.
    2. -
  2. Let intrinsics be CreateIntrinsics(realmRec).
    3. -
  3. Set realmRec.[[globalThis]] to undefined.
    4. -
  4. Set realmRec.[[globalEnv]] to undefined.
    5. -
  5. Set each of realmRec.[[directEvalTranslate]], realmRec.[[nonEvalFallback]], and - realmRec.[[indirectEval]] to undefined.
    6. -
  6. Return realmRec.
    7. -
-
- -
-

8.2.2 - CreateIntrinsics ( realmRec ) Abstract Operation

- -

When the abstract operation CreateIntrinsics with argument realmRec performs the following:

- -
    -
  1. Let intrinsics be a new Record.
    2. -
  2. Set realmRec.[[intrinsics]] to intrinsics.
    3. -
  3. Let objProto be ObjectCreate(null).
    4. -
  4. Set intrinsics.[[%ObjectPrototype%]] to objProto.
    5. -
  5. Let throwerSteps be the algorithm steps of the %ThrowTypeError% function - (9.2.8.1).
    6. -
  6. Let thrower be a new built-in function object that when called performs the action described by - steps.
    7. -
  7. Call the [[SetPrototypeOf]] internal method of thrower with argument undefined.
    8. -
  8. Set the [[Realm]] internal slot of thrower to - realmRec.
    9. -
  9. Perform DefinePropertyOrThrow(thrower, "caller", - PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false, [[Configurable]]: - false}).
    10. -
  10. Perform DefinePropertyOrThrow(thrower , "arguments", - PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false, [[Configurable]]: - false}).
    11. -
  11. Assert: Defining the above two properties will not result in an abrupt completion.
    12. -
  12. Set intrinsics.[[%ThrowTypeError%]] to thrower.
    13. -
  13. Let noStep be an empty sequence of algorithm steps.
    14. -
  14. Let funcProto be the CreateBuildinFunction(realmRec, noSteps, objProto).
    15. -
  15. Set intrinsics.[[%FunctionPrototype%]] to funcProto.
    16. -
  16. Call the [[SetPrototypeOf]] internal method of thrower with argument funcProto.
    17. -
  17. Set fields of intrinsics with the values listed in Table 7 that have not already been - handled above. The field names are the names listed in column one of the table. The value of each field is a new - object value fully and recursively populated with property values as defined by the specification of each object in - clauses 18-26. All object property values are newly created object values. All values that are built-in function - objects are created by performing CreateBuiltinFunction(realmRec, - <steps>, <prototype>, <slots>) where <steps> is the definition of that function provided by - this specification, <prototype> is the specified value of the function’s [[Prototype]] internal slot and <slots> is a list of the names, if - any, of the functions specified internal slots. The create of the intrinsics and their properties must be ordered to - avoid any dependencies upon objects that have not yet been created.
    18. -
  18. Return intrinsics.
    19. -
-
- -
-

8.2.3 - SetRealmGlobalObj ( realmRec, globalObj ) Abstract Operation

- -

The abstract operation SetRealmGlobalObj with arguments realmRec and globalObj performs the - following steps:

- -
    -
  1. If globalObj is undefined, then -
      -
    1. Let globalObj be ObjectCreate(realmRec.[[instrinsics]].[[%ObjectPrototype%]]).
      2. -
    -
    2. -
  2. Assert: Type(globalObj) is Object.
    3. -
  3. Set realmRec.[[globalThis]] be newGlobal.
    4. -
  4. Let newGlobalEnv be NewGlobalEnvironment(newGlobal).
    5. -
  5. Set realmRec.[[globalEnv]] be newGlobalEnv.
    6. -
  6. Return realmRec.
    7. -
-
- -
-

8.2.4 SetDefaultGlobalBindings ( realmRec ) Abstract Operation

- -

The abstract operation SetDefaultGlobalBindings with argument realmRec performs the following steps:

- -
    -
  1. Let global be realmRec.[[globalThis]].
    2. -
  2. For each property of the Global Object specified in clause 18, do -
      -
    1. Let name be the string value of the property name.
      2. -
    2. Let desc be the fully populated data property descriptor for the property containing the specified - attributes for the property. For properties whose values are functions, the value of the [[Value]] attribute is - the corresponding intrinsic function object from realmRec.
      3. -
    3. Let status be DefinePropertyOrThrow(global, name, - desc).
      4. -
    4. ReturnIfAbrupt(status).
      5. -
    -
    3. -
  3. Return global.
    4. -
-
-
- -
-
-

8.3 - Execution Contexts

- -

An execution context is a specification device that is used to track the runtime evaluation of code by an - ECMAScript implementation. At any point in time, there is at most one execution context that is actually executing code. - This is known as the running execution context. A stack is used to track execution contexts. The running execution - context is always the top element of this stack. A new execution context is created whenever control is transferred from the - executable code associated with the currently running execution context to executable code that is not associated with that - execution context. The newly created execution context is pushed onto the stack and becomes the running execution - context.

- -

An execution context contains whatever implementation specific state is necessary to track the execution progress of its - associated code. Each execution context has at least the state components listed in Table 21.

- -
-
Table 21 —State Components for All Execution Contexts
- - - - - - - - - - - - - -
ComponentPurpose
code evaluation stateAny state needed to perform, suspend, and resume evaluation of the code associated with this execution context.
RealmThe Realm from which associated code accesses ECMAScript resources.
-
- -

Evaluation of code by the running execution context may be suspended at various points defined within this specification. - Once the running execution context has been suspended a different execution context may become the running execution context - and commence evaluating its code. At some later time a suspended execution context may again become the running execution - context and continue evaluating its code at the point where it had previously been suspended. Transition of the running - execution context status among execution contexts usually occurs in stack-like last-in/first-out manner. However, some - ECMAScript features require non-LIFO transitions of the running execution context.

- -

The value of the Realm component of the running execution context is also called the - current Realm.

- -

Execution contexts for ECMAScript code have the additional state components listed in Table - 22.

- -
-
Table 22 — Additional State Components for ECMAScript Code Execution Contexts
- - - - - - - - - - - - - -
ComponentPurpose
LexicalEnvironmentIdentifies the Lexical Environment used to resolve identifier references made by code within this execution context.
VariableEnvironmentIdentifies the Lexical Environment whose environment record holds bindings created by VariableStatements within this execution context.
-
- -

The LexicalEnvironment and VariableEnvironment components of an execution context are always Lexical Environments. When - an execution context is created its LexicalEnvironment and VariableEnvironment components initially have the same value. The - value of the VariableEnvironment component never changes while the value of the LexicalEnvironment component may change - during execution of code within an execution context.

- -

Execution contexts representing the evaluation of generator objects have the additional state components listed in Table 23.

- -
-
Table 23 — Additional State Components for Generator Execution Contexts
- - - - - - - - - -
ComponentPurpose
GeneratorThe GeneratorObject that this execution context is evaluating.
-
- -

In most situations only the running execution context (the top of the execution context stack) is directly manipulated by - algorithms within this specification. Hence when the terms “LexicalEnvironment”, and - “VariableEnvironment” are used without qualification they are in reference to those components of the running - execution context.

- -

An execution context is purely a specification mechanism and need not correspond to any particular artefact of an - ECMAScript implementation. It is impossible for ECMAScript code to directly access or observe an execution context.

-
- -
-

8.3.1 - ResolveBinding ( name ) Abstract Operation

- -

The ResolveBinding abstract operation is used to determine the binding of name passed as a string value using - the LexicalEnvironment of the running execution - context. During execution of ECMAScript code, ResolveBinding is performed using the following algorithm:

- -
    -
  1. Let env be the running execution context’s LexicalEnvironment.
    2. -
  2. If the syntactic production that is being evaluated is contained in strict mode - code, then let strict be true, else let strict be false.
    3. -
  3. Return GetIdentifierReference(env, name, strict ).
    4. -
- -
-

NOTE The result of ResolveBinding is always a Reference value with its referenced name component equal to the name - argument.

-
-
- -
-

8.3.2 - GetThisEnvironment ( ) Abstract Operation

- -

The abstract operation GetThisEnvironment finds the lexical environment that currently supplies the binding of the keyword - this. GetThisEnvironment performs the following steps:

- -
    -
  1. Let lex be the running execution context’s LexicalEnvironment.
    2. -
  2. Repeat -
      -
    1. Let envRec be lex’s environment record.
      2. -
    2. Let exists be the result of calling the HasThisBinding concrete method of envRec.
      3. -
    3. If exists is true, then return envRec.
      4. -
    4. Let outer be the value of lex’s outer environment - reference.
      5. -
    5. Let lex be outer.
      6. -
    -
    3. -
- -
-

NOTE The loop in step 2 will always terminate because the llst of environments always ends with - the global environment which has a this binding.

-
-
- -
-

8.3.3 - ResolveThisBinding ( ) Abstract Operation

- -

The abstract operation ResolveThisBinding determines the binding of the keyword this using the LexicalEnvironment of the running execution - context. ResolveThisBinding performs the following steps:

- -
    -
  1. Let env be GetThisEnvironment( ).
    2. -
  2. Return the result of calling the GetThisBinding concrete method of env.
    3. -
-
- -
-

8.3.4 - GetGlobalObject ( ) Abstract Operation

- -

The abstract operation GetGlobalObject returns the global object used - by the currently running execution context. GetGlobalObject performs the following steps:

- -
    -
  1. Let ctx be the running execution context.
    2. -
  2. Let currentRealm be ctx’s Realm.
    3. -
  3. Return currentRealm.[[globalThis]].
    4. -
-
-
- -
-
-

8.4 Tasks - and Task Queues

- -

A Task is an abstract operation that initiates an ECAMScript computation when no other ECMAScript computation is - currently in progress. A Task abstract operation may be defined to accept an arbitrary set of task parameters.

- -

Execution of a Task can be initiated only when there is no running execution - context and the execution context stack is empty. A PendingTask is a request for - the future execution of a Task. A PendingTask is an internal Record whose fields are specified in Table - 24.

- -
-
Table 24 — PendingTask Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValueMeaning
[[Task]]The name of a Task abstract operationThis is the abstract operation that is performed when execution of this PendingTask is initiated. Tasks are abstract operations that use NextTask rather than Return to indicate that they have completed.
[[Arguments]]A List.The List of argument values that are to be passed to [[Task]] when it is activated.
[[Realm]]A Realm RecordThe Realm for the initial execution context when this Pending Task is initiated.
[[HostDefined]]Any, default value is undefined.Field reserved for use by host environment that need to associate additional information with a pending Task
-
- -

A Task Queue is a FIFO queue of PendingTask records. Each Task Queue has a name and the full set of available Task Queues - are defined by an ECMAScript implementation. Every ECMAScript implementation has at least the task queues defined in Table 25.

- -
-
Table 25 — Required Task Queues
- - - - - - - - - - - - - -
NamePurpose
ScriptTasksTasks that validate and evaluate ECMAScript Script and Module code units. See clauses 10 and 15.
PromiseTasksTasks that are responses to the settlement of a Promise (see 25.4).
-
- -

A request for the future execution of a Task is made by enqueueing, on a Task Queue, a PendingTask record that includes a - Task abstract operation name and any necessary argument values. When there is no running execution context and the execution context stack - is empty, the ECMAScript implementation removes the first PendingTask from a Task Queue and uses the information contained - in it to create an execution context and starts execution of the associated Task - abstract operation.

- -

The PendingTask records from a single Task Queue are always initiated in FIFO order. This specification does not define - the order in which multiple Task Queues are serviced. An ECMAScript implementation may interweave the FIFO evaluation of the - PendingTask records of a Task Queue with the evaluation of the PendingTask records of one or more other Task Queues. An - implementation must define what occurs when there are no running execution context and - all Task Queues are empty.

- -
-

NOTE Typically an ECMAScript implementation will have its Task Queues are pre-initialized with - at least one PendingTask and one of those Tasks will be the first to be executed. An implementation might choose to free - all resources and terminate if the current Task completes and all Task Queues are empty. Alternatively, it might choose to - wait for a some implementation specific agent or mechanism to enqueue new PendingTask requests.

-
- -

The following abstract operations are used to create and manage Tasks and Task Queues:

-
- -
-

8.4.1 EnqueueTask - ( queueName, task, arguments) Abstract Operation

- -

The abstract operation requires three arguments: queueName, task, and arguments. It - performs the following steps:

- -
    -
  1. Assert: Type(queueName) is String and its value is the name of a Task - Queue recognized by this implementation.
    2. -
  2. Assert: task is the name of a Task.
    3. -
  3. Assert: arguments is a List that has the same number of elements as the number of - parameters required by task.
    4. -
  4. Let callerContext be the running execution context.
    5. -
  5. Let callerRealm be callerContext’s Realm.
    6. -
  6. Let pending be PendingTask{ [[Task]]: task, [[Arguments]]: arguments, [[Realm]]: - callerRealm, [[HostDefined]]: undefined }.
    7. -
  7. Perform any implementation or host environment defined processing of pending. This may including modify the - [[HostDefined]] field or any other field of pending.
    8. -
  8. Add pending at the back of the Task Queue named by queueName.
    9. -
  9. Return NormalCompletion(empty).
    10. -
-
- -
-

8.4.2 - NextTask result

- -

An algorithm step such as:

- -
    -
  1. NextTask result.
    2. -
- -

is used in Task abstract operations in place of:

- -
    -
  1. Return result.
    2. -
- -

Task abstract operations must not contain a Return step or a ReturnIfAbrupt step. The - NextTask result operation is equivalent to the following steps:

- -
    -
  1. If result is an abrupt completion, then perform - implementation defined unhandled exception processing.
    2. -
  2. Suspend the running execution - context.
    3. -
  3. Assert: The execution context stack is - now empty.
    4. -
  4. Let nextQueue be a non-empty Task Queue chosen in an implementation defined manner. If all Task Queues are - empty, the result is implementation defined.
    5. -
  5. Let nextPending be the PendingTask record at the front of nextQueue. Remove that record from - nextQueue.
    6. -
  6. Let newContext be a new execution context.
    7. -
  7. Set newContext’s Realm to nextPending.[[Realm]].
    8. -
  8. Push newContext onto the execution context stack; newContext is - now the running execution context.
    9. -
  9. Perform any implementation or host environment defined task initialization using nextPending.
    10. -
  10. Perform the abstract operation named by nextPending.[[Task]] using the elements of - nextPending.[[Arguments]] as its arguments.
    11. -
-
-
- -
-
-

8.5 - Initialization

- -

An ECMAScript implementation performs the following steps prior to the execution of any Tasks or the evaluation of any - ECMAScript code:

- -
    -
  1. Let realm be CreateRealm().
    2. -
  2. Let newContext be a new exeution context.
    3. -
  3. Set newContext’s Realm to realm.
    4. -
  4. Push newContext onto the execution context stack; newContext is - now the running execution context.
    5. -
  5. Let status be InitializeFirstRealm(realm).
    6. -
  6. If status is an abrupt completion, then -
      -
    1. Assert: The first realm could not be created.
      2. -
    2. Terminate ECMAScript execution.
      3. -
    -
    7. -
  7. In an implementation dependent manner, obtain the SourceCharacter sequence (see 10) for one or more ECMAScript - scripts. For each such sequence source do, -
      -
    1. EnqueueTask("ScriptTasks", ScriptEvaluationTask, (source)).
      2. -
    -
    8. -
  8. NextTask NormalCompletion(undefined).
    9. -
-
- -
-

8.5.1 - InitializeFirstRealm ( realm ) Abstract Operation

- -

The abstract operation InitializeFirstRealm with parameter realm performs the following steps:

- -
    -
  1. Let intrinsics be CreateIntrinsics(realm).
    2. -
  2. If this implementation requires use of an exotic object object to serve as realm’s global object, then - let global be such an object created in an implementation defined manner. Otherwise, let global be - undefined indicating that an ordinary object should be created as the global object.
    3. -
  3. Perfrom SetRealmGlobalObject(realm, global).
    4. -
  4. Let globalObj be SetDefaultGlobalBindings(realm).
    5. -
  5. ReturnIfAbrupt(globalObj).
    6. -
  6. Create any implementation defined global object properties on globalObj.
    7. -
  7. Return NormalCompletion(undefined).
    8. -
-
-
-
- -
-
-

9 Ordinary and Exotic Objects Behaviours

-
- -
-
-

9.1 Ordinary Object Internal Methods and Internal Slots

- -

All ordinary objects have an internal slot called - [[Prototype]]. The value of this internal slot is either - null or an object and is used for implementing inheritance. Data properties of the [[Prototype]] object are inherited - (are visible as properties of the child object) for the purposes of get access, but not for set access. Accessor properties - are inherited for both get access and set access.

- -

Every ordinary object has a Boolean-valued [[Extensible]] internal slot that controls whether or not properties may be - added to the object. If the value of the [[Extensible]] internal - slot is false then additional properties may not be added to the object. In addition, if [[Extensible]] is - false the value of the [[Prototype]] internal slot of - the object may not be modified. Once the value of an object’s [[Extensible]] internal slot has been set to false it may not be - subsequently changed to true.

- -

In the following algorithm descriptions, assume O is an ordinary object, P is a property key value, V is any ECMAScript - language value, and Desc is a Property - Descriptor record.

-
- -
-

9.1.1 [[GetPrototypeOf]] ( )

- -

When the [[GetPrototypeOf]] internal method of O is called the following steps are taken:

- -
    -
  1. Return the value of the [[Prototype]] internal slot of - O.
    2. -
-
- -
-

9.1.2 [[SetPrototypeOf]] (V)

- -

When the [[SetPrototypeOf]] internal method of O is called with argument V the following steps are - taken:

- -
    -
  1. Assert: Either Type(V) is Object or Type(V) is Null.
    2. -
  2. Let extensible be the value of the [[Extensible]] internal slot of O.
    3. -
  3. Let current be the value of the [[Prototype]] internal slot of O.
    4. -
  4. If SameValue(V, current), then return true.
    5. -
  5. If extensible is false, then return false.
    6. -
  6. If V is not null, then -
      -
    1. Let p be V.
      2. -
    2. Repeat, while p is not null -
        -
      1. If SameValue(p, O) is true, then return false.
        2. -
      2. Let nextp be the result of calling the [[GetPrototypeOf]] internal method of p with no - arguments.
        3. -
      3. ReturnIfAbrupt(nextp).
        4. -
      4. Let p be nextp.
        5. -
      -
      3. -
    -
    7. -
  7. Let extensible be the value of the [[Extensible]] internal slot of O.
    8. -
  8. If extensible is false, then -
      -
    1. Let current2 be the value of the [[Prototype]] internal slot of O.
      2. -
    2. If SameValue(V, current2) is true, then return true.
      3. -
    3. Return false.
      4. -
    -
    9. -
  9. Set the value of the [[Prototype]] internal slot of - O to V.
    10. -
  10. Return true.
    11. -
-
- -
-

9.1.3 [[IsExtensible]] ( )

- -

When the [[IsExtensible]] internal method of O is called the following steps are taken:

- -
    -
  1. Return the value of the [[Extensible]] internal slot of - O.
    2. -
-
- -
-

9.1.4 [[PreventExtensions]] ( )

- -

When the [[PreventExtensions]] internal method of O is called the following steps are taken:

- -
    -
  1. Set the value of the [[Extensible]] internal slot of - O to false.
    2. -
  2. Return true.
    3. -
-
- -
-
-

9.1.5 [[GetOwnProperty]] (P)

- -

When the [[GetOwnProperty]] internal method of O is called with property key - P, the following steps are taken:

- -
    -
  1. Return OrdinaryGetOwnProperty(O, P).
    2. -
-
- -
-

9.1.5.1 OrdinaryGetOwnProperty (O, P)

- -

When the abstract operation OrdinaryGetOwnProperty is called with Object O and with property key P, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. If O does not have an own property with key P, return undefined.
    3. -
  3. Let D be a newly created Property Descriptor with - no fields.
    4. -
  4. Let X be O’s own property whose key is P.
    5. -
  5. If X is a data property, then -
      -
    1. Set D.[[Value]] to the value of X’s [[Value]] attribute.
      2. -
    2. Set D.[[Writable]] to the value of X’s [[Writable]] attribute
      3. -
    -
    6. -
  6. Else X is an accessor property, so -
      -
    1. Set D.[[Get]] to the value of X’s [[Get]] attribute.
      2. -
    2. Set D.[[Set]] to the value of X’s [[Set]] attribute.
      3. -
    -
    7. -
  7. Set D.[[Enumerable]] to the value of X’s [[Enumerable]] attribute.
    8. -
  8. Set D.[[Configurable]] to the value of X’s [[Configurable]] attribute.
    9. -
  9. Return D.
    10. -
-
-
- -
-
-

9.1.6 [[DefineOwnProperty]] (P, Desc)

- -

When the [[DefineOwnProperty]] internal method of O is called with property - key P and Property Descriptor Desc, the following steps are taken:

- -
    -
  1. Return OrdinaryDefineOwnProperty(O, P, Desc).
    2. -
-
- -
-

9.1.6.1 OrdinaryDefineOwnProperty (O, P, Desc)

- -

When the abstract operation OrdinaryDefineOwnProperty is called with - Object O, property key P, and Property Descriptor Desc the following steps are taken:

- -
    -
  1. Let current be the result of calling the [[GetOwnProperty]] internal method of O with argument - P.
    2. -
  2. ReturnIfAbrupt(current).
    3. -
  3. Let extensible be the value of the [[Extensible]] internal slot of O.
    4. -
  4. Return ValidateAndApplyPropertyDescriptor(O, P, - extensible, Desc, current).
    5. -
-
- -
-

9.1.6.2 IsCompatiblePropertyDescriptor (Extensible, Desc, Current)

- -

When the abstract operation IsCompatiblePropertyDescriptor is called - with Boolean value Extensible, and Property Descriptors Desc, and Current the following steps are taken:

- -
    -
  1. Return ValidateAndApplyPropertyDescriptor(undefined, - undefined, Extensible, Desc, Current).
    2. -
-
- -
-

9.1.6.3 ValidateAndApplyPropertyDescriptor (O, P, extensible, Desc, - current)

- -

When the abstract operation ValidateAndApplyPropertyDescriptor is - called with Object O, property key P, Boolean value extensible, and Property Descriptors Desc, and - current the following steps are taken:

- -

This algorithm contains steps that test various fields of the Property Descriptor Desc for specific - values. The fields that are tested in this manner need not actually exist in Desc. If a field is - absent then its value is considered to be false.

- -
-

NOTE If undefined is passed as the O argument only validation is performed and - no object updates are performed.

-
- -
    -
  1. Assert: If O is not undefined then P is a valid property key.
    2. -
  2. If current is undefined, then -
      -
    1. If extensible is false, then return false.
      2. -
    2. Assert: extensible is true.
      3. -
    3. If IsGenericDescriptor(Desc) or IsDataDescriptor(Desc) is true, then -
        -
      1. If O is not undefined, then create an own data property named P of object O - whose [[Value]], [[Writable]], [[Enumerable]] and [[Configurable]] attribute values are described by - Desc. If the value of an attribute field of Desc is absent, the attribute of the newly created - property is set to its default value.
        2. -
      -
      4. -
    4. Else Desc must be an accessor Property - Descriptor, -
        -
      1. If O is not undefined, then create an own accessor property named P of object O - whose [[Get]], [[Set]], [[Enumerable]] and [[Configurable]] attribute values are described by Desc. - If the value of an attribute field of Desc is absent, the attribute of the newly created property is - set to its default value.
        2. -
      -
      5. -
    5. Return true.
      6. -
    -
    3. -
  3. Return true, if every field in Desc is absent.
    4. -
  4. Return true, if every field in Desc also occurs in current and the value of every field in - Desc is the same value as the corresponding field in current when compared using the SameValue algorithm.
    5. -
  5. If the [[Configurable]] field of current is false then -
      -
    1. Return false, if the [[Configurable]] field of Desc is true.
      2. -
    2. Return false, if the [[Enumerable]] field of Desc is present and the [[Enumerable]] fields of - current and Desc are the Boolean negation of each other.
      3. -
    -
    6. -
  6. If IsGenericDescriptor(Desc) is true, then no further - validation is required.
    7. -
  7. Else if IsDataDescriptor(current) and IsDataDescriptor(Desc) have different results, then -
      -
    1. Return false, if the [[Configurable]] field of current is false.
      2. -
    2. If IsDataDescriptor(current) is true, then -
        -
      1. If O is not undefined, then convert the property named P of object O from a data - property to an accessor property. Preserve the existing values of the converted property’s - [[Configurable]] and [[Enumerable]] attributes and set the rest of the property’s attributes to their - default values.
        2. -
      -
      3. -
    3. Else, -
        -
      1. If O is not undefined, then convert the property named P of object O from an - accessor property to a data property. Preserve the existing values of the converted property’s - [[Configurable]] and [[Enumerable]] attributes and set the rest of the property’s attributes to their - default values.
        2. -
      -
      4. -
    -
    8. -
  8. Else if IsDataDescriptor(current) and IsDataDescriptor(Desc) are both true, then -
      -
    1. If the [[Configurable]] field of current is false, then -
        -
      1. Return false, if the [[Writable]] field of current is false and the [[Writable]] field - of Desc is true.
        2. -
      2. If the [[Writable]] field of current is false, then -
          -
        1. Return false, if the [[Value]] field of Desc is present and SameValue(Desc.[[Value]], current.[[Value]]) is - false.
          2. -
        -
        3. -
      -
      2. -
    2. Else the [[Configurable]] field of current is true, so any change is acceptable.
      3. -
    -
    9. -
  9. Else IsAccessorDescriptor(current) and IsAccessorDescriptor(Desc) are both true, -
      -
    1. If the [[Configurable]] field of current is false, then -
        -
      1. Return false, if the [[Set]] field of Desc is present and SameValue(Desc.[[Set]], current.[[Set]]) is false.
        2. -
      2. Return false, if the [[Get]] field of Desc is present and SameValue(Desc.[[Get]], current.[[Get]]) is false.
        3. -
      -
      2. -
    -
    10. -
  10. If O is not undefined, then -
      -
    1. For each field of Desc that is present, set the corresponding attribute of the property named P of - object O to the value of the field. The [[Origin]] field, if present, is ignored.
      2. -
    -
    11. -
  11. Return true.
    12. -
- -
-

NOTE Step 8.b allows any field of Desc to be different from the corresponding field of - current if current’s [[Configurable]] field is true. This even permits changing the [[Value]] of a property - whose [[Writable]] attribute is false. This is allowed because a true [[Configurable]] attribute would - permit an equivalent sequence of calls where [[Writable]] is first set to true, a new [[Value]] is set, and then - [[Writable]] is set to false.

-
-
-
- -
-

9.1.7 [[HasProperty]](P)

- -

When the [[HasProperty]] internal method of O is called with property key - P, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let hasOwn be the result of calling the [[GetOwnProperty]] internal method of O with argument - P.
    3. -
  3. ReturnIfAbrupt(hasOwn).
    4. -
  4. If hasOwn is not undefined, then return true.
    5. -
  5. Let parent be the result of calling the [[GetPrototypeOf]] internal method of O.
    6. -
  6. ReturnIfAbrupt(parent).
    7. -
  7. If parent is not null, then -
      -
    1. Return the result of calling the [[HasProperty]] internal method of parent with argument P.
      2. -
    -
    8. -
  8. Return false.
    9. -
-
- -
-

9.1.8 [[Get]] (P, Receiver)

- -

When the [[Get]] internal method of O is called with property key P - and ECMAScript language value Receiver the following - steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let desc be the result of calling the [[GetOwnProperty]] internal method of O with argument - P.
    3. -
  3. ReturnIfAbrupt(desc).
    4. -
  4. If desc is undefined, then -
      -
    1. Let parent be the result of calling the [[GetPrototypeOf]] internal method of O.
      2. -
    2. ReturnIfAbrupt(parent).
      3. -
    3. If parent is null, then return undefined.
      4. -
    4. Return the result of calling the [[Get]] internal method of parent with arguments P and - Receiver.
      5. -
    -
    5. -
  5. If IsDataDescriptor(desc) is true, return - desc.[[Value]].
    6. -
  6. Otherwise, IsAccessorDescriptor(desc) must be true so, let - getter be desc.[[Get]].
    7. -
  7. If getter is undefined, return undefined.
    8. -
  8. Return the result of calling the [[Call]] internal method of getter with Receiver as the - thisArgument and an empty List as - argumentsList.
    9. -
-
- -
-

9.1.9 [[Set]] ( P, V, Receiver)

- -

When the [[Set]] internal method of O is called with property key P, - value V, and ECMAScript language value Receiver, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let ownDesc be the result of calling the [[GetOwnProperty]] internal method of O with argument - P.
    3. -
  3. ReturnIfAbrupt(ownDesc).
    4. -
  4. If ownDesc is undefined, then -
      -
    1. Let parent be the result of calling the [[GetPrototypeOf]] internal method of O.
      2. -
    2. ReturnIfAbrupt(parent).
      3. -
    3. If parent is not null, then -
        -
      1. Return the result of calling the [[Set]] internal method of parent with arguments P, V, - and Receiver.
        2. -
      -
      4. -
    4. Else, -
        -
      1. Let ownDesc be the PropertyDescriptor{[[Value]]: undefined, [[Writable]]: true, - [[Enumerable]]: true, [[Configurable]]: true}.
        2. -
      -
      5. -
    -
    5. -
  5. If IsDataDescriptor(ownDesc) is true, then -
      -
    1. If ownDesc.[[Writable]] is false, return false.
      2. -
    2. If Type(Receiver) is not Object, return - false.
      3. -
    3. Let existingDescriptor be the result of calling the [[GetOwnProperty]] internal method of Receiver - with argument P.
      4. -
    4. ReturnIfAbrupt(existingDescriptor).
      5. -
    5. If existingDescriptor is not undefined, then -
        -
      1. Let valueDesc be the PropertyDescriptor{[[Value]]: V}.
        2. -
      2. Return the result of calling the [[DefineOwnProperty]] internal method of Receiver with arguments - P and valueDesc.
        3. -
      -
      6. -
    6. Else Receiver does not currently have a property P, -
        -
      1. Return CreateDataProperty(Receiver, P, V).
        2. -
      -
      7. -
    -
    6. -
  6. If IsAccessorDescriptor(ownDesc) is true, then -
      -
    1. Let setter be ownDesc.[[Set]].
      2. -
    2. If setter is undefined, return false.
      3. -
    3. Let setterResult be the result of calling the [[Call]] internal method of setter providing - Receiver as thisArgument and a new List - containing V as argumentsList.
      4. -
    4. ReturnIfAbrupt(setterResult).
      5. -
    5. Return true.
      6. -
    -
    7. -
-
- -
-

9.1.10 [[Delete]] (P)

- -

When the [[Delete]] internal method of O is called with property key - P the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let desc be the result of calling the [[GetOwnProperty]] internal method of O with argument - P.
    3. -
  3. ReturnIfAbrupt(desc).
    4. -
  4. If desc is undefined, then return true.
    5. -
  5. If desc.[[Configurable]] is true, then -
      -
    1. Remove the own property with name P from O.
      2. -
    2. Return true.
      3. -
    -
    6. -
  6. Return false.
    7. -
-
- -
-

9.1.11 [[Enumerate]] ()

- -

When the [[Enumerate]] internal method of O is called the following steps are taken:

- -
    -
  1. Return an Iterator object (25.1.2) whose next method iterates over all the - String-valued keys of enumerable properties of O. The mechanics and order of enumerating the properties is not - specified but must conform to the rules specified below.
    2. -
- -

Enumerated properties do not include properties whose property key is a Symbol. Properties - of the object being enumerated may be deleted during enumeration. If a property that has not yet been visited during - enumeration is deleted, then it will not be visited. If new properties are added to the object being enumerated during - enumeration, the newly added properties are not guaranteed to be visited in the active enumeration. A property name must not - be visited more than once in any enumeration.

- -

Enumerating the properties of an object includes enumerating properties of its prototype, and the prototype of the - prototype, and so on, recursively; but a property of a prototype is not enumerated if it is “shadowed” because - some previous object in the prototype chain has a property with the same name. The values of [[Enumerable]] attributes are - not considered when determining if a property of a prototype object is shadowed by a previous object on the prototype - chain.

- -

The following is an informative algorithm that conforms to these rules

- -
    -
  1. Let proto be the result of calling the [[GetPrototypeOf]] internal method of O with no arguments.
    2. -
  2. ReturnIfAbrupt(proto).
    3. -
  3. If proto is the value null, then -
      -
    1. Let propList be a new empty List.
      2. -
    -
    4. -
  4. Else -
      -
    1. Let propList be the result of calling the [[Enumerate]] internal method of proto.
      2. -
    -
    5. -
  5. ReturnIfAbrupt(propList).
    6. -
  6. For each name that is the property key of an own property of O -
      -
    1. If Type(name) is String, then -
        -
      1. Let desc be the result of calling the [[GetOwnProperty]] internal method of O with argument - name.
        2. -
      2. ReturnIfAbrupt(desc).
        3. -
      3. If name is an element of propList, then remove name as an element of - propList.
        4. -
      4. If desc.[[Enumerable]] is true, then add name as an element of propList.
        5. -
      -
      2. -
    -
    7. -
  7. Order the elements of propList in an implementation defined order.
    8. -
  8. Return propList.
    9. -
-
- -
-

9.1.12 [[OwnPropertyKeys]] ( )

- -

When the [[OwnPropertyKeys]] internal method of O is called the following steps are taken:

- -
    -
  1. Let keys be a new empty List.
    2. -
  2. For each own property key P of O that is an integer index, in ascending - numeric index order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    3. -
  3. For each own property key P of O that is a String but is not an integer - index, in property creation order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    4. -
  4. For each own property key P of O that is a Symbol, in property creation - order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    5. -
  5. Return CreateArrayFromList(keys).
    6. -
-
- -
-

9.1.13 - ObjectCreate(proto, internalSlotsList) Abstract Operation

- -

The abstract operation ObjectCreate with argument proto (an object or null) is used to specify the runtime - creation of new ordinary objects. The optional argument internalSlotsList is a List of the names of additional internal slots that must be defined as - part of the object. If the list is not provided, an empty List is - used. This abstract operation performs the following steps:

- -
    -
  1. If internalSlotsList was not provided, let internalSlotsList be an empty List.
    2. -
  2. Let obj be a newly created object with an internal - slot for each name in internalSlotsList.
    3. -
  3. Set obj’s essential internal methods to the default ordinary object definitions specified in 9.1.
    4. -
  4. Set the [[Prototype]] internal slot of obj to - proto.
    5. -
  5. Set the [[Extensible]] internal slot of obj to - true.
    6. -
  6. Return obj.
    7. -
-
- -
-

9.1.14 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto, - internalSlotsList )

- -

The abstract operation OrdinaryCreateFromConstructor creates an ordinary object whose [[Prototype]] value is retrieved - from a constructor’s prototype property, if it exists. Otherwise the supplied default is used for - [[Prototype]]. The optional internalSlotsList is a List of - the names of additional internal slots that must be defined as part of the object. If the list is not provided, an empty List is used. This abstract operation performs the following steps:

- -
    -
  1. Assert: intrinsicDefaultProto is a string value that is this - specification’s name of an intrinsic object. The corresponding object must be an intrinsic that is intended to - be used as the [[Prototype]] value of an object.
    2. -
  2. Let proto be GetPrototypeFromConstructor(constructor, - intrinsicDefaultProto).
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Return ObjectCreate(proto, internalSlotsList).
    5. -
-
-
- -
-
-

9.2 - ECMAScript Function Objects

- -

ECMAScript function objects encapsulate parameterized ECMAScript code closed over a lexical environment and support the dynamic evaluation of that code. An ECMAScript - function object is an ordinary object and has the same internal slots and (except as noted below) and the same internal - methods as other ordinary objects. The code of an ECMAScript function object may be either strict mode code (10.2.1) or non-strict mode code.

- -

ECMAScript function objects have the additional internal slots listed in Table 26.

- -

ECMAScript function objects whose code is not strict mode code (10.2.1) provide an alternative definition for the [[GetOwnProperty]] internal method. This - alternative prevents the value of strict mode function from being revealed as the value of a function object property named - "caller". The alternative definition exist solely to preclude a non-standard legacy feature of some ECMAScript - implementations from revealing information about strict mode callers. If an implementation does not provide such a feature, - it need not implement this alternative internal method for ECMAScript function objects. ECMAScript function objects are - considered to be ordinary objects even though they may use the alternative definition of [[GetOwnProperty]].

- -
-
Table 26 — Internal Slots of ECMAScript Function Objects
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Internal SlotTypeDescription
[[Environment]]Lexical EnvironmentThe Lexical Environment that the function was closed over. Used as the outer environment when evaluating the code of the function.
[[FormalParameters]]Parse NodeThe root parse node of the source code that defines the function’s formal parameter list.
[[FunctionKind]]StringEither "normal" or "generator".
[[Code]]Parse NodeThe root parse node of the source code that defines the function’s body.
[[Realm]]Realm RecordThe Code Realm in which the function was created and which provides any intrinsic objects that are accessed when evaluating the function.
[[ThisMode]](lexical, strict, global)Defines how this references are interpreted within the formal parameters and code body of the function. lexical means that this refers to the this value of a lexically enclosing function. strict means that the this value is used exactly as provided by an invocation of the function. global means that a this value of undefined is interpreted as a reference to the global object.
[[Strict]]Booleantrue if this is a strict mode function, false if this is not a strict mode function.
[[NeedsSuper]]Booleantrue if this function uses super.
[[HomeObject]]ObjectIf the function uses super, this is the object whose [[GetPrototypeOf]] provides the object where super property lookups begin.
[[MethodName]]String or SymbolIf the function uses super, this is the property key that is used for unqualified references to super.
-
- -

All ECMAScript function objects have the [[Call]] internal method defined here. ECMAScript functions that are also - constructors in addition have the [[Construct]] internal method. ECMAScript function objects whose code is not strict mode code have the [[Get]] and [[GetOwnProperty]] internal methods defined here.

-
- -
-

9.2.1 [[GetOwnProperty]] (P)

- -

When the [[GetOwnProperty]] internal method of non-strict ECMAScript function - object F is called with property key P, the following steps are - taken:

- -
    -
  1. Let v be OrdinaryGetOwnProperty(F, P).
    2. -
  2. If IsDataDescriptor(v) is true, then -
      -
    1. If P is "caller" then, -
        -
      1. Let callerValue be v.[[Value]].
        2. -
      2. If callerValue is an ECMAScript Function object, then -
          -
        1. If callerValue’s [[Strict]] internal slot is true, then set - v.[[Value]] to null.
          2. -
        -
        3. -
      -
      2. -
    -
    3. -
  3. Return v.
    4. -
- -

If an implementation does not provide a built-in caller property for non-strict ECMAScript function objects - then it must not use this definition. Instead the ordinary object [[GetOwnProperty]] internal method is used.

-
- -
-

9.2.2 [[Call]] ( thisArgument, argumentsList)

- -

The [[Call]] internal method for an ECMAScript function object - F is called with parameters thisArgument and argumentsList, a List of ECMAScript language - values. The following steps are taken:

- -
    -
  1. If F’s [[Code]] internal slot has the value - undefined, then throw a TypeError exception.
    2. -
  2. Let callerContext be the running execution context.
    3. -
  3. If callerContext is not already suspended, then Suspend callerContext.
    4. -
  4. Let calleeContext be a new ECMAScript Code execution context.
    5. -
  5. Let calleeRealm be the value of F’s [[Realm]] internal slot.
    6. -
  6. Set calleeContext’s Realm to calleeRealm.
    7. -
  7. Let thisMode be the value of F’s [[ThisMode]] internal slot.
    8. -
  8. Let needsThisWrapper be false.
    9. -
  9. If thisMode is lexical, then -
      -
    1. Let localEnv be the result of calling NewDeclarativeEnvironment passing the value of the [[Environment]] internal slot of F as the argument.
      2. -
    -
    10. -
  10. Else, -
      -
    1. If thisMode is strict, then let thisValue be - thisArgument.
      2. -
    2. Else -
        -
      1. if thisArgument is null or undefined, then -
          -
        1. Let thisValue be calleeRealm.[[globalThis]].
          2. -
        -
        2. -
      2. Else -
          -
        1. if Type(thisArgument) is not Object, then let - needsThisWrapper be true.
          2. -
        2. Let thisValue be thisArgument.
          3. -
        -
        3. -
      -
      3. -
    3. Let localEnv be NewFunctionEnvironment(F, - thisValue).
      4. -
    4. ReturnIfAbrupt(localEnv).
      5. -
    5. NOTE Any exception objects produced by NewFunctionEnvironment are associated with callerReam.
      6. -
    -
    11. -
  11. Set the LexicalEnvironment of calleeContext to localEnv.
    12. -
  12. Set the VariableEnvironment of calleeContext to localEnv.
    13. -
  13. Push calleeContext onto the execution context stack; calleeContext - is now the running execution context.
    14. -
  14. If needsThisWrapper is true then, -
      -
    1. Let wrapperedThis be ToObject(thisArgument).
      2. -
    2. Assert: wrapperedThis is not an abrupt completion.
      3. -
    3. NOTE Wrappering deferred until calleeContext is running so that ToObject produces objects - using calleeRealm.
      4. -
    4. Let functionEnv be localEnv’s environment record.
      5. -
    5. Set functionEnv’s thisValue to wrapperedThis.
      6. -
    -
    15. -
  15. Let status be the result of performing FunctionDeclarationInstantiation using the function F, - argumentsList , and localEnv as described in 9.2.13.
    16. -
  16. If status is an abrupt completion, then -
      -
    1. Remove calleeContext from the execution context stack and restore - callerContext as the running execution context.
      2. -
    2. Return status.
      3. -
    -
    17. -
  17. Let result be the result of EvaluateBody of the production that is the value of F's [[Code]] internal slot passing F as the argument.
    18. -
  18. Remove calleeContext from the execution context stack and restore - callerContext as the running execution context.
    19. -
  19. Return result.
    20. -
- -
-

NOTE 1 Most ECMAScript functions use a Function - Environment Record as their LexicalEnvironment. ECMAScript functions that are - arrow functions use a Declarative Environment Record as their LexicalEnvironment.

-
- -
-

NOTE 2 When calleeContext is removed from the - execution context stack it must not be destroyed because it may have been suspended and retained by a generator object for later resumption.

-
-
- -
-

9.2.3 - [[Construct]] ( argumentsList)

- -

The [[Construct]] internal method for an ECMAScript Function object - F is called with a single parameter argumentsList which is a possibly empty List of ECMAScript language - values. The following steps are taken:

- -
    -
  1. Return Construct(F, argumentsList).
    2. -
-
- -
-

9.2.4 - FunctionAllocate (functionPrototype, strict) Abstract Operation

- -

The abstract operation FunctionAllocate requires the two arguments functionPrototype and strict. It also accepts one optional argument, functionKind. - FunctionAllocate performs the following steps:

- -
    -
  1. Assert: Type(functionPrototype) is Object.
    2. -
  2. Assert: If functionKind is present, its value is either - "normal" or "generator".
    3. -
  3. If functionKind is not present, then let functionKind be "normal".
    4. -
  4. Let F be a newly created ECMAScript function object with the - internal slots listed in Table 26. All of those internal slots are initialized to - undefined.
    5. -
  5. Set F’s essential internal methods except for [[GetOwnProperty]] to the default ordinary object - definitions specified in 9.1.
    6. -
  6. If strict is true, set F’s [[GetOwnProperty]] internal method to the default ordinary - object definitions specified in 9.1.
    7. -
  7. Else, set F’s [[GetOwnProperty]] internal method to the definitions specified in Error! Reference source not found..
    8. -
  8. Set F’s [[Call]] internal method to the definition specified in 9.2.1.
    9. -
  9. Set the [[Strict]] internal slot of F to - strict.
    10. -
  10. Set the [[FunctionKind]] internal slot of F to - functionKind.
    11. -
  11. Set the [[Prototype]] internal slot of F to - functionPrototype.
    12. -
  12. Set the [[Extensible]] internal slot of F to - true.
    13. -
  13. Set the [[Realm]] internal slot of F to the running execution context’s Realm.
    14. -
  14. Return F.
    15. -
-
- -
-

9.2.5 - FunctionInitialize (F, kind, Strict, ParameterList, Body, Scope) Abstract Operation

- -

The abstract operation FunctionInitialize requires the arguments: a function object F, kind which - is one of (Normal, Method, Arrow), a Boolean Strict, a parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope. FunctionInitialize performs the following steps:

- -
    -
  1. Let len be the ExpectedArgumentCount of ParameterList.
    2. -
  2. Let realm be the value of F’s [[Realm]] internal slot.
    3. -
  3. Let status be DefinePropertyOrThrow(F, "length", - PropertyDescriptor{[[Value]]: len, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true}).
    4. -
  4. ReturnIfAbrupt(status).
    5. -
  5. If Strict is true, then -
      -
    1. Let status be AddRestrictedFunctionProperties(F, - realm).
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    6. -
  6. Set the [[Strict]] internal slot of F to - Strict.
    7. -
  7. Set the [[Environment]] internal slot of F to the - value of Scope.
    8. -
  8. Set the [[FormalParameters]] internal slot of F - to ParameterList .
    9. -
  9. Set the [[Code]] internal slot of F to - Body.
    10. -
  10. If kind is Arrow, then set the [[ThisMode]] internal slot of F to lexical.
    11. -
  11. Else if Strict is true, then set the [[ThisMode]] internal slot of F to strict.
    12. -
  12. Else set the [[ThisMode]] internal slot of F to - global.
    13. -
  13. Return F.
    14. -
-
- -
-

9.2.6 - FunctionCreate (kind, ParameterList, Body, Scope, Strict) Abstract Operation

- -

The abstract operation FunctionCreate requires the arguments: kind which is one of (Normal, Method, Arrow), a - parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope, a Boolean flag Strict, and optionally, an object functionPrototype. FunctionCreate performs the following steps:

- -
    -
  1. If the functionPrototype argument was not passed, then -
      -
    1. Let functionPrototype be the intrinsic object %FunctionPrototype%.
      2. -
    -
    2. -
  2. Let F be FunctionAllocate(functionPrototype, Strict).
    3. -
  3. Return FunctionInitialize(F, kind, Strict, - ParameterList, Body, Scope).
    4. -
-
- -
-

9.2.7 - GeneratorFunctionCreate (kind, ParameterList, Body, Scope, Strict) Abstract Operation

- -

The abstract operation GeneratorFunctionCreate requires the arguments: kind which is one of (Normal, Method, - Arrow), a parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope, and a Boolean flag Strict. GeneratorFunctionCreate performs the following - steps:

- -
    -
  1. Let functionPrototype be the intrinsic object %Generator%.
    2. -
  2. Let F be FunctionAllocate(functionPrototype, Strict, - "generator").
    3. -
  3. Return FunctionInitialize(F, kind, Strict, - ParameterList, Body, Scope).
    4. -
-
- -
-
-

9.2.8 AddRestrictedFunctionProperties ( F, realm ) Abstract Operation

- -

The abstract operation AddRestrictedFunctionProperties is called with a function object F and Realm Record realm as its argument. It performs the following steps:

- -
    -
  1. Let thrower be realmRec.[[intrinsics]].[[%ThrowTypeError%]]
    2. -
  2. Let status be DefinePropertyOrThrow(F, "caller", - PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false, - [[Configurable]]: false}).
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Return DefinePropertyOrThrow(F , "arguments", - PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false, - [[Configurable]]: false}).
    5. -
-
- -
-

9.2.8.1 - %ThrowTypeError% ( )

- -

The %ThrowTypeError% intrinsic is an anonymous built-in function object that is defined once for each Realm. When %ThrowTypeError% is called it performs the following steps:

- -
    -
  1. Throw a TypeError exception.
    2. -
- -

The value of the [[Extensible]] internal slot of a - %ThrowTypeError% function is false.

-
-
- -
-

9.2.9 - MakeConstructor (F, writablePrototype, prototype) Abstract Operation

- -

The abstract operation MakeConstructor requires a Function argument F and optionally, a Boolean - writablePrototype and an object prototype. If prototype is provided it is assumed to - already contain, if needed, a "constructor" property whose value is F. This operation converts - F into a constructor by performing the following steps:

- -
    -
  1. Assert: F is an ECMAScript - function object.
    2. -
  2. Let installNeeded be false.
    3. -
  3. If the prototype argument was not provided, then -
      -
    1. Let installNeeded be true.
      2. -
    2. Let prototype be ObjectCreate(%ObjectPrototype%).
      3. -
    -
    4. -
  4. If the writablePrototype argument was not provided, then -
      -
    1. Let writablePrototype be true.
      2. -
    -
    5. -
  5. Set F’s essential internal method [[Construct]] to the definition specified in 9.2.3.
    6. -
  6. If installNeeded, then -
      -
    1. Let status be DefinePropertyOrThrow(prototype, - "constructor", PropertyDescriptor{[[Value]]: F, [[Writable]]: writablePrototype, - [[Enumerable]]: false, [[Configurable]]: writablePrototype }).
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    7. -
  7. Let status be DefinePropertyOrThrow(F, - "prototype", PropertyDescriptor{[[Value]]: prototype, [[Writable]]: writablePrototype, - [[Enumerable]]: false, [[Configurable]]: false}).
    8. -
  8. ReturnIfAbrupt(status).
    9. -
  9. Return NormalCompletion(undefined).
    10. -
-
- -
-

9.2.10 MakeMethod - ( F, methodName, homeObject) Abstract Operation

- -

The abstract operation MakeMethod with arguments F, methodName and homeObject configures - F as a method by performing the following steps:

- -
    -
  1. Assert: F is an ECMAScript - function object.
    2. -
  2. Assert: methodName is either undefined or a property key.
    3. -
  3. Assert: Type(homeObject ) is either Undefined or Object.
    4. -
  4. Set the [[NeedsSuper]] internal slot of F to - true.
    5. -
  5. Set the [[HomeObject]] internal slot of F to - homeObject.
    6. -
  6. Set the [[MethodName]] internal slot of F to - methodName.
    7. -
  7. Return NormalCompletion(undefined).
    8. -
-
- -
-

9.2.11 - SetFunctionName (F, name, prefix) Abstract Operation

- -

The abstract operation SetFunctionName requires a Function argument F, a String or Symbol argument - name and optionally a String argument prefix. This operation adds a name property to - F by performing the following steps:

- -
    -
  1. Assert: F is an extensible ECMAScript function object that does not have a name own - property.
    2. -
  2. Assert: Type(name) - is either Symbol or String.
    3. -
  3. If Type(name) is Symbol, then -
      -
    1. Let description be name’s [[Description]] value.
      2. -
    2. If description is undefined, then let name be the empty String.
      3. -
    3. Else, let name be the concatenation of "[", description, and "]".
      4. -
    -
    4. -
  4. If name is not the empty string and prefix was passed, then let name be the concatenation of - prefix, Unicode code point U+0020 (Space) , and name.
    5. -
  5. Call the [[DefineOwnProperty]] internal method of F with arguments "name" and - PropertyDescriptor{[[Value]]: name, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true}.
    6. -
  6. Assert: Defining the name property will always succeed.
    7. -
  7. Return NormalCompletion(undefined).
    8. -
-
- -
-

9.2.12 - CloneMethod(function, newHome, newName) Abstract Operation

- -

The abstract operation Clone is called with a function object function, an object newHome, and a property key newName as its argument. It performs the following steps:

- -
    -
  1. Assert: function is an ECMAScript function object or an exotic Built-in function object.
    2. -
  2. Assert: Type(newHome) is Object.
    3. -
  3. Assert: Type(newName) one of Undefined, String, or Symbol.
    4. -
  4. If function is an ECMAScript function, then -
      -
    1. Let new be a new ECMAScript function object that has all of - the same internal methods and internal slots as function.
      2. -
    -
    5. -
  5. Else -
      -
    1. Assert: function is an exotic Built-in function object.
      2. -
    2. Let new be a new exotic Built-in function object that has all of the same internal methods and internal - slots as function.
      3. -
    -
    6. -
  6. Set the value of each of new’s internal slots, except for [[Extensible]], [[HomeObject]] and - [[MethodName]] to the value of function’s corresponding internal slot.
    7. -
  7. Set new’s [[Extensible]] internal slot to - true.
    8. -
  8. If the value of function’s [[NeedsSuper]] internal slot is true, then -
      -
    1. Set the value of new’s [[HomeObject]] internal slot to newHome.
      2. -
    2. If newName is not undefined, then -
        -
      1. Set the value of new’s [[MethodName]] internal slot to newName.
        2. -
      -
      3. -
    3. Else, -
        -
      1. Set the value of new’s [[MethodName]] internal slot to the value of - function’s [[MethodName]] internal - slot.
        2. -
      -
      4. -
    -
    9. -
  9. If function is an exotic Built-in function object or if function’s [[Strict]] internal slot is true, then -
      -
    1. Let realm be new’s [[Realm]] internal slot.
      2. -
    2. Let status be AddRestrictedFunctionProperties(new, realm).
      3. -
    3. ReturnIfAbrupt(status).
      4. -
    -
    10. -
  10. Return new.
    11. -
- -
-

NOTE The purpose of this abstract operation is to create a new function object that is - identical to the argument object in all always except for its identity and the value of its [[HomeObject]] internal slot. However, properties of the function object, - except for the restricted function properties, are not created or copied.

-
-
- -
-

9.2.13 FunctionDeclarationInstantiation(func, argumentsList, env ) Abstract - Operation

- -
-

NOTE When an execution context is established for - evaluating an ECMAScript function a new Declarative Environment Record - is created and bindings for each formal parameter are instantiated in that environment record. Each declaration in the - function body is also instantiated. If the function’s formal parameters do not include any default value - initializers then the body declarations are instantiated in the same environment record as the parameters. If default - value parameter initializers exist, a second environment record is created for the body declarations. Formal parameters - and functions are initialized as part of FunctionDeclarationInstantiation. All other bindings are initialized during - evaluation of the function body.

-
- -

FunctionDeclarationInstantiation is performed as follows using arguments func, argumentsList, and - env. func is the function object that for which the execution - context is being established. env is the declarative - environment record in which formal parameter bindings are to be created.

- -
    -
  1. Let code be the value of the [[Code]] internal - slot of func.
    2. -
  2. Let strict be the value of the [[Strict]] internal - slot of func.
    3. -
  3. Let formals be the value of the [[FormalParameters]] internal slot of func.
    4. -
  4. Let parameterNames be the BoundNames of formals.
    5. -
  5. If parameterNames has any duplicate entries, let hasDuplicates be true. Otherwise, let - hasDuplicates be false.
    6. -
  6. Let needsParameterEnvironment be ContainsExpression of formals.
    7. -
  7. Let simpleParameterList be IsSimpleParameterList of formals.
    8. -
  8. Let varNames be the VarDeclaredNames of code.
    9. -
  9. Let varDeclarations be the VarScopedDeclarations of code.
    10. -
  10. Let lexicalNames be the LexicallyDeclaredNames of code.
    11. -
  11. Let functionNames be an empty List.
    12. -
  12. Let functionsToInitialize be an empty List.
    13. -
  13. For each d in varDeclarations, in reverse list order do -
      -
    1. If d is neither a VariableDeclaration or a ForBinding, then -
        -
      1. Assert: d is either a FunctionDeclaration or a - GeneratorDeclaration.
        2. -
      2. Let fn be the sole element of the BoundNames of d.
        3. -
      3. If fn is not an element of functionNames, then -
          -
        1. Insert fn as the first element of functionNames.
          2. -
        2. NOTE If there are multiple FunctionDeclarations or - GeneratorDeclarations for the same name, the last declaration is used.
          3. -
        3. Insert d as the first element of functionsToInitialize.
          4. -
        -
        4. -
      -
      2. -
    -
    14. -
  14. Let needsSpecialArgumentsBinding be true.
    15. -
  15. Let argumentsObjectNeeded be true.
    16. -
  16. If the value of the [[ThisMode]] internal slot of - func is lexical, then -
      -
    1. NOTE Arrow functions never have an arguments objects.
      2. -
    2. Let needsSpecialArgumentsBinding be false.
      3. -
    3. Let argumentsObjectNeeded be false.
      4. -
    -
    17. -
  17. Else if "arguments" is an element of parameterNames, then -
      -
    1. Let needsSpecialArgumentsBinding be false.
      2. -
    2. Let argumentsObjectNeeded be false.
      3. -
    -
    18. -
  18. Else -
      -
    1. If "arguments" is an element of functionNames, then let argumentsObjectNeeded be - false.
      2. -
    2. Else if "arguments" is an element of lexicalNames, then let argumentsObjectNeeded be - false.
      3. -
    -
    19. -
  19. If argumentsObjectNeeded is false, then let ao be undefined.
    20. -
  20. Else, -
      -
    1. If strict is true or if simpleParameterList is false, then -
        -
      1. Let ao be CreateUnmappedArgumentsObject(argumentsList).
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let ao be CreateMappedArgumentsObject(func, - formals, argumentsList, env).
        2. -
      -
      3. -
    3. ReturnIfAbrupt(ao).
      4. -
    -
    21. -
  21. For each String paramName in parameterNames, do -
      -
    1. Let alreadyDeclared be the result of calling env’s HasBinding concrete method passing - paramName as the argument.
      2. -
    2. NOTE Early errors ensure that duplicate parameter names can only occur in non-strict functions that do not have - parameter default values or rest parameters.
      3. -
    3. If alreadyDeclared is false, then -
        -
      1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - paramName as the argument.
        2. -
      2. If hasDuplicates is true, then -
          -
        1. Let status be the result of calling env’s InitializeBinding concrete method passing - paramName and undefined as the argument.
          2. -
        -
        3. -
      3. Assert: status is never an abrupt completion for either of the above - operations.
        4. -
      -
      4. -
    -
    22. -
  22. Let instantiatedVarNames be a copy of the List - parameterNames.
    23. -
  23. If needsSpecialArgumentsBinding is true, then -
      -
    1. If strict is true, then -
        -
      1. Let status be the result of calling env’s CreateImmutableBinding concrete method passing - "arguments" as the argument.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - "arguments" as the argument.
        2. -
      -
      3. -
    3. Assert: status is never an abrupt completion
      4. -
    4. If argumentsObjectNeeded is true, then -
        -
      1. Call env’s InitializeBinding concrete method passing "arguments" and ao as - arguments.
        2. -
      -
      5. -
    5. Append "arguments" to instantiatedVarNames.
      6. -
    -
    24. -
  24. If hasDuplicates is true, then -
      -
    1. Let formalStatus be the result of performing IteratorBindingInitialization for formals with CreateListIterator(argumentsList) and undefined as - arguments.
      2. -
    -
    25. -
  25. Else, -
      -
    1. Let formalStatus be the result of performing IteratorBindingInitialization for formals with CreateListIterator(argumentsList) and env as arguments.
      2. -
    -
    26. -
  26. ReturnIfAbrupt(formalStatus).
    27. -
  27. If needsSpecialArgumentsBinding is true and argumentsObjectNeeded is false, then -
      -
    1. Call env’s InitializeBinding concrete method passing "arguments" and undefined as - arguments.
      2. -
    -
    28. -
  28. If needsParameterEnvironment is true, then -
      -
    1. NOTE A separate enviornment record is needed to ensure that closures created by parameter default value - expressions do not have visibility of declarations in the function body.
      2. -
    2. Let env be NewDeclarativeEnvironment(env).
      3. -
    3. Let calleeContext be the running execution context.
      4. -
    4. Set the LexicalEnvironment of calleeContext to env.
      5. -
    5. Set the VariableEnvironment of calleeContext to env.
      6. -
    -
    29. -
  29. For each n in varNames, do -
      -
    1. If n is not an element of instantiatedVarNames, then -
        -
      1. Append n to instantiatedVarNames.
        2. -
      2. Let status be the result of calling env’s CreateMutableBinding concrete method passing - n as the argument.
        3. -
      3. Assert: status is never an abrupt completion.
        4. -
      4. Call env’s InitializeBinding concrete method passing n and undefined as - arguments.
        5. -
      5. NOTE vars and functions whose names are the same as a formal parameter, use the same binding element as - the parameter.
        6. -
      -
      2. -
    -
    30. -
  30. Let lexDeclarations be the LexicallyScopedDeclarations of code.
    31. -
  31. For each element d in lexDeclarations do -
      -
    1. NOTE A lexically declared name cannot be the same as a function/generator declaration, formal parameter, or a - var name. Lexically declared names are only instantiated here but not initialized.
      2. -
    2. For each element dn of the BoundNames of d do -
        -
      1. If IsConstantDeclaration of d is true, then -
          -
        1. Let status be the result of calling env’s CreateImmutableBinding concrete method - passing dn as the argument.
          2. -
        -
        2. -
      2. Else, -
          -
        1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - dn and false as the arguments.
          2. -
        -
        3. -
      -
      3. -
    3. Assert: status is never an abrupt completion.
      4. -
    -
    32. -
  32. For each production f in functionsToInitialize, do -
      -
    1. Let fn be the sole element of the BoundNames of f.
      2. -
    2. Let fo be the result of performing InstantiateFunctionObject for f with argument env.
      3. -
    3. Let fref be ResolveBinding(fn).
      4. -
    4. Let status be PutValue(fref, fo).
      5. -
    5. Assert: status is never an abrupt completion.
      6. -
    -
    33. -
  33. Return NormalCompletion(empty).
    34. -
- -
-

NOTE B.3.2 - provides an extension to the above algorithm that is necessary for backwards compatability with web browser - implementations of ECAMScript that predate the sixth edition of ECMA-262.

-
-
-
- -
-
-

9.3 - Built-in Function Objects

- -

The built-in function objects defined in this specification may be implemented as either ECMAScript function objects (9.2) whose behaviour is provided using ECMAScript code or as implementation - provided exotic function objects whose behaviour is provided in some other manner. In either case, the effect of calling - such functions must conform to their specifications.

- -

If a built-in function object is implemented as an exotic object it must have the ordinary object behaviour specified in - 9.1 except [[GetOwnProperty]] which must be as - specified in 9.2.1. All such exotic function objects also - have [[Prototype]] and [[Extensible]] internal slots.

- -

Unless otherwise specified every built-in function object initially has the %FunctionPrototype% object (19.2.3) as the initial value of its [[Prototype]] internal slot.

- -

The behaviour specified for each built-in function via algorithm steps or other means is the specification of the - [[Call]] behaviour for that function with the [[Call]] thisArgument providing the this - value and the [[Call]] argumentsList providing the named parameters for each built-in function. If the built-in - function is implemented as an ECMAScript function object then this specified - behaviour must be implemented by the ECMAScript code that is the body of the function. Built-in functions that are - ECMAScript function objects must be strict mode functions.

- -

Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method - unless otherwise specified in the description of a particular function. When a built-in constructor is called as part of a - new expression the argumentsList parameter of the invoked [[Construct]] internal method provides the - values for the built-in constructor’s named parameters.

- -

Built-in functions that are not constructors do not have a prototype property unless otherwise specified in - the description of a particular function.

- -

If a built-in function object is not implemented as an ECMAScript function it must have a [[Realm]] internal slot. It must also have a [[Call]] internal method that - conforms to the following definition:

-
- -
-

9.3.1 [[Call]] ( thisArgument, argumentsList)

- -

The [[Call]] internal method for a built-in function object F is called with parameters - thisArgument and argumentsList, a List of ECMAScript language values. The following steps are taken:

- -
    -
  1. Let callerContext be the running execution context.
    2. -
  2. If callerContext is not already suspended, then Suspend callerContext.
    3. -
  3. Let calleeContext be a new execution context.
    4. -
  4. Let calleeRealm be the value of F’s [[Realm]] internal slot.
    5. -
  5. Set calleeContext’s Realm to calleeRealm.
    6. -
  6. Perform any necessary implementation defined initialization of calleeContext.
    7. -
  7. Push calleeContext onto the execution context stack; calleeContext - is now the running execution context.
    8. -
  8. Let result be the Completion Record that is the result - of evaluating F in an implementation defined manner that conforms to this specification of F.
    9. -
  9. Remove calleeContext from the execution context stack and restore - callerContext as the running execution context.
    10. -
  10. Return result.
    11. -
- -
-

NOTE 1 When calleeContext is removed from the - execution context stack it must not be destroyed because it may have been suspended and retained by a generator object for later resumption.

-
-
- -
-

9.3.2 - CreateBuiltinFunction(realm, steps, prototype, internalSlotsList) Abstract Operation

- -

The abstract operation CreateBuiltinFunction takes arguments realm, - prototype, and steps. The optional argument internalSlotsList is a List of the names of additional internal slot that must be defined as part of the object. If the - list is not provided, an empty List is used. CreateBuiltinFunction - returns a built-in function object created by the following steps:

- -
    -
  1. Assert: realm is a Realm Record.
    2. -
  2. Assert: steps is either a set of algorithm steps or other definition - of a functions behaviour provided in this specification.
    3. -
  3. Let func be a new built-in function object that when called performs the action described by steps. The - new function object has internal slots whose names are the elements of internalSlotsList. The initial value of - each of those internal slots is undefined.
    4. -
  4. Set the [[Realm]] internal slot of func to - realm.
    5. -
  5. Call the [[SetPrototypeOf]] internal method of func with argument prototype.
    6. -
  6. Perform the AddRestrictedFunctionProperties(func, - realm).
    7. -
  7. Return func.
    8. -
-
-
- -
-
-

9.4 Built-in Exotic Object Internal Methods and Data Fields

- -

This specification defines several kinds of built-in exotic objects. These objects generally behave similar to ordinary - objects except for a few specific situations. The following exotic objects use the ordinary object internal methods except - where it is explicitly specified otherwise below:

-
- -
-
-

9.4.1 Bound Function Exotic Objects

- -

A bound function is an exotic object that wrappers another function object. A bound function is callable (it has - a [[Call]] internal method and may have a [[Construct]] internal method). Calling a bound function generally results in a - call of its wrapped function.

- -

Bound function objects do not have the internal slots of ECMAScript function objects defined in Table 26. Instead they have the internal slots defined in Table 27.

- -
-
Table 27 — Internal Slots of Exotic Bound Function Objects
- - - - - - - - - - - - - - - - - - - - - -
Internal SlotTypeDescription
[[BoundTargetFunction]]Callable ObjectThe wrappered function object.
[[BoundThis]]AnyThe value that is always passed as the this value when calling the wrappered function.
[[BoundArguments]]List of AnyA list of values that whose elements are used as the first arguments to any call to the wrappered function.
-
- -

Unlike ECMAScript function objects, bound function objects do not use alternative definitions of the [[Get]] and - [[GetOwnProperty]] internal methods. Bound function objects provide all of the essential internal methods as specified in - 9.1. However, they use the following definitions - for the essential internal methods of function objects.

-
- -
-

9.4.1.1 - [[Call]]

- -

When the [[Call]] internal method of an exotic bound function object, - F, which was created using the bind function is called with parameters thisArgument and - argumentsList, a List of ECMAScript language values, the following steps are taken:

- -
    -
  1. Let boundArgs be the value of F’s [[BoundArguments]] internal slot.
    2. -
  2. Let boundThis be the value of F’s [[BoundThis]] - internal slot.
    3. -
  3. Let target be the value of F’s [[BoundTargetFunction]] internal slot.
    4. -
  4. Let args be a new list containing the same values as the list boundArgs in the same order followed by - the same values as the list argumentsList in the same order.
    5. -
  5. Return the result of calling the [[Call]] internal method of target providing boundThis as - thisArgument and providing args as argumentsList.
    6. -
-
- -
-

9.4.1.2 [[Construct]]

- -

When the [[Construct]] internal method of an exotic bound function - object, F that was created using the bind function is called with a list of arguments ExtraArgs, the following steps are taken:

- -
    -
  1. Let target be the value of F’s [[BoundTargetFunction]] internal slot.
    2. -
  2. Assert: target has a [[Construct]] internal method.
    3. -
  3. Let boundArgs be the value of F’s [[BoundArguments]] internal slot.
    4. -
  4. Let args be a new list containing the same values as the list boundArgs in the same order followed by - the same values as the list ExtraArgs in the same order.
    5. -
  5. Return the result of calling the [[Construct]] internal method of target providing args as the - arguments.
    6. -
-
- -
-

9.4.1.3 BoundFunctionCreate (targetFunction, boundThis, boundArgs) Abstract - Operation

- -

The abstract operation BoundFunctionCreate with arguments targetFunction, boundThis and - boundArgs is used to specify the creation of new Bound - Function exotic objects. It performs the following steps:

- -
    -
  1. Let proto be the intrinsic %FunctionPrototype%.
    2. -
  2. Let obj be a newly created object.
    3. -
  3. Set obj’s essential internal methods to the default ordinary object definitions specified in 9.1.
    4. -
  4. Set the [[Call]] internal method of obj as described in 9.4.1.1.
    5. -
  5. If targetFunction has a [[Construct]] internal method, then -
      -
    1. Set the [[Construct]] internal method of obj as described in 9.4.1.2.
      2. -
    -
    6. -
  6. Set the [[Prototype]] internal slot of obj to - proto.
    7. -
  7. Set the [[Extensible]] internal slot of obj to - true.
    8. -
  8. Set the [[BoundTargetFunction]] internal slot of obj to - targetFunction.
    9. -
  9. Set the [[BoundThis]] internal slot of obj to the value of - boundThis.
    10. -
  10. Set the [[BoundArguments]] internal slot of obj to boundArgs.
    11. -
  11. Return obj.
    12. -
-
- -
-

9.4.1.4 BoundFunctionClone ( function ) Abstract Operation

- -

The abstract operation BoundFunctionClone is called with argujment function it performs the following - steps:

- -
    -
  1. Assert: function is a Bound Function exotic object.
    2. -
  2. Assert: Type(newHome) is Object.
    3. -
  3. Let new be a new Bound Function exotic object that has all - of the same internal methods and internal slots as function.
    4. -
  4. Set the value of each of new’s internal slots, except for [[Extensible]] to the value of - function’s corresponding internal - slot.
    5. -
  5. Set new’s [[Extensible]] internal slot to - true.
    6. -
  6. Let realm be BoundFunctionTargetRealm(new).
    7. -
  7. Let status be AddRestrictedFunctionProperties(new, - realm).
    8. -
  8. ReturnIfAbrupt(status).
    9. -
  9. Return new.
    10. -
-
- -
-

9.4.1.5 BoundFunctionTargetRealm ( bound ) Abstract Operation

- -

The abstract operation BoundFunctionTargetRealm with argument bound performs the following steps:

- -
    -
  1. Assert: bound is a Bound Function exotic object.
    2. -
  2. Let target be bound’s [[BoundTargetFunction]] - internal slot.
    3. -
  3. If target is a Bound Function exotic object, then -
      -
    1. Return BoundFunctionTargetRealm(target).
      2. -
    -
    4. -
  4. If target has a [[Realm]] internal slot, then -
      -
    1. Return target’s [[Realm]] internal - slot.
      2. -
    -
    5. -
  5. Return the running execution context’s Realm.
    6. -
- -
-

NOTE Step 5 will only be reached if target is a non-standard exotic function object - that does not have a [[Realm]] internal slot.

-
-
-
- -
-
-

9.4.2 - Array Exotic Objects

- -

An Array object is an exotic object that gives special treatment to array index property keys (see 6.1.7). A property whose property name is an array index is also called an element. - Every Array object has a length property whose value is always a nonnegative integer less than 232. The value of the length property is numerically - greater than the name of every property whose name is an array index; whenever a property of an Array object is created or - changed, other properties are adjusted as necessary to maintain this invariant. Specifically, whenever a property is added - whose name is an array index, the length property is changed, if necessary, to be one more than the numeric - value of that array index; and whenever the length property is changed, every property whose name is an array - index whose value is not smaller than the new length is automatically deleted. This constraint applies only to own - properties of an Array object and is unaffected by length or array index properties that may be inherited - from its prototypes.

- -
-

NOTE A String property name P is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 232−1.

-
- -

Exotic Array objects have the same internal slots as ordinary objects. They also have an [[ArrayInitializationState]] - internal slot.

- -

Exotic Array objects always have a non-configurable property named "length".

- -

Exotic Array objects provide an alternative definition for the [[DefineOwnProperty]] internal method. Except for that - internal method, exotic Array objects provide all of the other essential internal methods as specified in 9.1.

-
- -
-

9.4.2.1 [[DefineOwnProperty]] ( P, Desc)

- -

When the [[DefineOwnProperty]] internal method of an exotic Array object A is called with property key P, and Property - Descriptor Desc the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. If P is "length", then -
      -
    1. Return ArraySetLength(A, Desc).
      2. -
    -
    3. -
  3. Else if P is an array index, then -
      -
    1. Let oldLenDesc be OrdinaryGetOwnProperty(A, - P).
      2. -
    2. Assert: oldLenDesc will never be undefined or an accessor - descriptor because Array objects are created with a length data property that cannot be deleted or - reconfigured.
      3. -
    3. Let oldLen be oldLenDesc.[[Value]].
      4. -
    4. Let index be ToUint32(P).
      5. -
    5. Assert: index will never be an abrupt completion.
      6. -
    6. If index ≥ oldLen and oldLenDesc.[[Writable]] is false, then return - false.
      7. -
    7. Let succeeded be the result of calling OrdinaryDefineOwnProperty passing A, P, and Desc - as arguments.
      8. -
    8. ReturnIfAbrupt(succeeded).
      9. -
    9. If succeeded is false, then return false.
      10. -
    10. If index ≥ oldLen -
        -
      1. Set oldLenDesc.[[Value]] to index + 1.
        2. -
      2. Let succeeded be OrdinaryDefineOwnProperty(A, - "length", oldLenDesc).
        3. -
      3. ReturnIfAbrupt(succeeded).
        4. -
      -
      11. -
    11. Return true.
      12. -
    -
    4. -
  4. Return OrdinaryDefineOwnProperty(A, P, Desc).
    5. -
-
- -
-

9.4.2.2 - ArrayCreate(length, proto) Abstract Operation

- -

The abstract operation ArrayCreate with argument length (a positive integer or undefined) and optional argument proto is used to specify the creation of new exotic Array - objects. It performs the following steps:

- -
    -
  1. Assert: length is either undefined or a integer Number ≥ - 0.
    2. -
  2. If length is −0, then let length be +0.
    3. -
  3. If the proto argument was not passed, then let proto be the intrinsic object %ArrayPrototype%.
    4. -
  4. Let A be a newly created Array exotic object.
    5. -
  5. Set A’s essential internal methods except for [[DefineOwnProperty]] to the default ordinary object - definitions specified in 9.1.
    6. -
  6. Set the [[DefineOwnProperty]] internal method of A as specified in 9.4.2.1.
    7. -
  7. Set the [[Prototype]] internal slot of A to - proto.
    8. -
  8. Set the [[Extensible]] internal slot of A to - true.
    9. -
  9. If length is not undefined, then -
      -
    1. Set the [[ArrayInitializationState]] internal slot - of A to true.
      2. -
    -
    10. -
  10. Else -
      -
    1. Set the [[ArrayInitializationState]] internal slot - of A to false.
      2. -
    2. Let length be +0.
      3. -
    -
    11. -
  11. If length>232-1, then throw a RangeError exception.
    12. -
  12. Call OrdinaryDefineOwnProperty with arguments A, - "length" and PropertyDescriptor{[[Value]]: length, [[Writable]]: true, [[Enumerable]]: - false, [[Configurable]]: false}.
    13. -
  13. Return A.
    14. -
-
- -
-

9.4.2.3 - ArraySetLength(A, Desc) Abstract Operation

- -

When the abstract operation ArraySetLength is called with an exotic Array object A, and Property Descriptor Desc the following steps are taken:

- -
    -
  1. If the [[Value]] field of Desc is absent, then -
      -
    1. Return OrdinaryDefineOwnProperty(A, - "length", Desc).
      2. -
    -
    2. -
  2. Let newLenDesc be a copy of Desc.
    3. -
  3. Let newLen be ToUint32(Desc.[[Value]]).
    4. -
  4. If newLen is not equal to ToNumber( Desc.[[Value]]), throw a - RangeError exception.
    5. -
  5. Set newLenDesc.[[Value]] to newLen.
    6. -
  6. Let oldLenDesc be the result of calling the [[GetOwnProperty]] internal method of A passing - "length" as the argument.
    7. -
  7. ReturnIfAbrupt(oldLenDesc).
    8. -
  8. Assert: oldLenDesc will never be undefined or an accessor - descriptor because Array objects are created with a length data property that cannot be deleted or - reconfigured.
    9. -
  9. Let oldLen be oldLenDesc.[[Value]].
    10. -
  10. If newLen ≥oldLen, then -
      -
    1. Return OrdinaryDefineOwnProperty(A, - "length", newLenDesc).
      2. -
    -
    11. -
  11. If oldLenDesc.[[Writable]] is false, then return false.
    12. -
  12. If newLenDesc.[[Writable]] is absent or has the value true, let newWritable be - true.
    13. -
  13. Else, -
      -
    1. Need to defer setting the [[Writable]] attribute to false in case any elements cannot be deleted.
      2. -
    2. Let newWritable be false.
      3. -
    3. Set newLenDesc.[[Writable]] to true.
      4. -
    -
    14. -
  14. Let succeeded be OrdinaryDefineOwnProperty(A, - "length", newLenDesc).
    15. -
  15. ReturnIfAbrupt(succeeded).
    16. -
  16. If succeeded is false, return false.
    17. -
  17. While newLen < oldLen repeat, -
      -
    1. Set oldLen to oldLen – 1.
      2. -
    2. Let deleteSucceeded be the result of calling the [[Delete]] internal method of A passing ToString(oldLen).
      3. -
    3. ReturnIfAbrupt(succeeded).
      4. -
    4. If deleteSucceeded is false, then -
        -
      1. Set newLenDesc.[[Value]] to oldLen+1.
        2. -
      2. If newWritable is false, set newLenDesc.[[Writable]] to false.
        3. -
      3. Let succeeded be OrdinaryDefineOwnProperty(A, - "length", newLenDesc).
        4. -
      4. ReturnIfAbrupt(succeeded).
        5. -
      5. Return false.
        6. -
      -
      5. -
    -
    18. -
  18. If newWritable is false, then -
      -
    1. Call OrdinaryDefineOwnProperty passing A, - "length", and PropertyDescriptor{[[Writable]]: false} as arguments. This call will - always return true.
      2. -
    -
    19. -
  19. Return true.
    20. -
- -
-

NOTE In steps 3 and 4, if Desc.[[Value]] is an object then its valueOf - method is called twice. This is legacy behaviour that was specified with this effect starting with the 2nd - Edition of this specification.

-
-
-
- -
-
-

9.4.3 - String Exotic Objects

- -

A String object is an exotic object that encapsulates a String value and exposes virtual integer indexed data - properties corresponding to the individual code unit elements of the string value. Exotic String objects always have a - data property named "length" whose value is the number of code unit elements in the encapsulated - String value. Both the code unit data properties and the "length" property are non-writable and - non-configurable.

- -

Exotic String objects have the same internal slots as ordinary objects. They also have a [[StringData]] internal - slot.

- -

Exotic String objects provide alternative definitions for the following internal methods. All of the other exotic - String object essential internal methods that are not defined below are as specified in 9.1.

-
- -
-

9.4.3.1 [[GetOwnProperty]] ( P )

- -

When the [[GetOwnProperty]] internal method of an exotic String object S is called with property key P the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let desc be OrdinaryGetOwnProperty(S, P).
    3. -
  3. If desc is not undefined return desc.
    4. -
  4. If Type(P) is not String, then return - undefined.
    5. -
  5. Let index be CanonicalNumericIndexString (P).
    6. -
  6. Assert: index is not an abrupt completion.
    7. -
  7. If index is undefined, then return undefined.
    8. -
  8. If IsInteger(index) is false, then return undefined.
    9. -
  9. If index = −0, then return undefined.
    10. -
  10. Let str be the String value of the [[StringData]] internal slot of S, if the value of [[StringData]] - is undefined the empty string is used as its value.
    11. -
  11. Let len be the number of elements in str.
    12. -
  12. If index < 0 or len ≤ index, return undefined.
    13. -
  13. Let resultStr be a String value of length 1, containing one code unit from str, specifically the code - unit at position index, where the first (leftmost) element in str is considered to be at position 0, - the next one at position 1, and so on.
    14. -
  14. Return a PropertyDescriptor{ [[Value]]: resultStr, [[Enumerable]]: true, [[Writable]]: false, - [[Configurable]]: false }.
    15. -
-
- -
-

9.4.3.2 [[Enumerate]] ()

- -

When the [[Enumerate]] internal method of an exotic String object O is called the following steps are - taken:

- -
    -
  1. Let indexKeys be a new empty List.
    2. -
  2. Let str be the String value of the [[StringData]] internal slot of O, if the value of [[StringData]] - is undefined the empty string is used as its value.
    3. -
  3. Let len be the number of elements in str.
    4. -
  4. For each integer i starting with 0 such that i < len, in ascending order, -
      -
    1. Add ToString(i) as the last element of indexKeys
      2. -
    -
    5. -
  5. Let ordinary be the result of calling the default ordinary object [[Enumerate]] internal method (9.1.11) on O.
    6. -
  6. ReturnIfAbrupt(ordinary).
    7. -
  7. Return CreateCompoundIterator(CreateListIterator(indexKeys), ordinary).
    8. -
-
- -
-

9.4.3.3 [[OwnPropertyKeys]] ( )

- -

When the [[OwnPropertyKeys]] internal method of a String exotic object - O is called the following steps are taken:

- -
    -
  1. Let keys be a new empty List.
    2. -
  2. Let str be the String value of the [[StringData]] internal slot of O, if the value of [[StringData]] - is undefined the empty string is used as its value.
    3. -
  3. Let len be the number of elements in str.
    4. -
  4. For each integer i starting with 0 such that i < len. in ascending order, -
      -
    1. Add ToString(i) as the last element of keys
      2. -
    -
    5. -
  5. For each own property key P of O such that P is an integer index - and ToInteger(P) ≥ len, in ascending numeric index order, -
      -
    1. Add P as the last element of keys.
      2. -
    -
    6. -
  6. For each own property key P of O such that Type(P) is String and P is not an integer index, in - property creation order, -
      -
    1. Add P as the last element of keys.
      2. -
    -
    7. -
  7. For each own property key P of O such that Type(P) is Symbol, in property creation order, -
      -
    1. Add P as the last element of keys.
      2. -
    -
    8. -
  8. Return CreateArrayFromList(keys).
    9. -
-
- -
-

9.4.3.4 - StringCreate Abstract Operation

- -

The abstract operation StringCreate with argument prototype is used to specify the creation of new exotic - String objects. It performs the following steps:

- -
    -
  1. Let A be a newly created String exotic object.
    2. -
  2. Set A’s essential internal methods to the default ordinary object definitions specified in 9.1.
    3. -
  3. Set the [[GetOwnProperty]] internal method of A as specified in 9.4.3.1.
    4. -
  4. Set the [[Enumerate]] internal method of A as specified in 9.4.3.2.
    5. -
  5. Set the [[OwnPropertyKeys]] internal method of A as specified in 9.4.3.3.
    6. -
  6. Set the [[Prototype]] internal slot of A to - prototype.
    7. -
  7. Set the [[Extensible]] internal slot of A to - true.
    8. -
  8. Return A.
    9. -
-
-
- -
-
-

9.4.4 Arguments Exotic Objects

- -

Most ECMAScript functions make an arguments objects available to their code. Depending upon the characteristics of the - function definition, its argument object is either an ordinary object or an arguments exotic object. An aguments - exotic object is an exotic object whose array index properties map to the formal parameters bindings of an invocation of - its associated ECMAScript function.

- -

Arguments exotic objects have the same internal slots as ordinary objects. They also have a [[ParameterMap]] internal - slot. Ordanary arguments objects also have a [[ParameterMap]] internal slot whose value is always undefined. For ordany - argument objects the [[ParameterMap]] internal slot is only used by Object.prototype.toString (19.1.3.6) to identify them as such.

- -

Arguments exotic objects provide alternative definitions for the following internal methods. All of the other exotic - arguments object essential internal methods that are not defined below are as specified in 9.1

- -
-

NOTE 1 For non-strict mode functions the integer indexed data properties of an arguments - object whose numeric name values are less than the number of formal parameters of the corresponding function object - initially share their values with the corresponding argument bindings in the function’s execution context. This means that changing the property changes the corresponding - value of the argument binding and vice-versa. This correspondence is broken if such a property is deleted and then - redefined or if the property is changed into an accessor property. For strict mode functions, the values of the - arguments object’s properties are simply a copy of the arguments passed to the function and there is no dynamic - linkage between the property values and the formal parameter values.

-
- -
-

NOTE 2 The ParameterMap object and its property values are used as a device for specifying - the arguments object correspondence to argument bindings. The ParameterMap object and the objects that are the values of - its properties are not directly observable from ECMAScript code. An ECMAScript implementation does not need to actually - create or use such objects to implement the specified semantics.

-
- -
-

NOTE 3 Arguments objects for strict mode functions define non-configurable accessor - properties named "caller" and "callee" which throw a TypeError exception on access. The - "callee" property has a more specific meaning for non-strict mode functions and a "caller" - property has historically been provided as an implementation-defined extension by some ECMAScript implementations. The - strict mode definition of these properties exists to ensure that neither of them is defined in any other manner by - conforming ECMAScript implementations.

-
-
- -
-

9.4.4.1 [[GetOwnProperty]] (P)

- -

The [[GetOwnProperty]] internal method of an arguments exotic object when called with a property name P - performs the following steps:

- -
    -
  1. Let args be the arguments object.
    2. -
  2. Let desc be OrdinaryGetOwnProperty(args, P).
    3. -
  3. If desc is undefined then return desc.
    4. -
  4. Let map be the value of the [[ParameterMap]] internal slot of the arguments object.
    5. -
  5. Let isMapped be the result of calling the [[GetOwnProperty]] internal method of map passing P - as the argument.
    6. -
  6. Assert: isMapped is never an abrupt completion.
    7. -
  7. If the value of isMapped is not undefined, then -
      -
    1. Set desc.[[Value]] to Get(map, P).
      2. -
    -
    8. -
  8. If IsDataDescriptor(desc) is true and P is - "caller" and desc.[[Value]] is a strict mode Function object, throw a TypeError - exception.
    9. -
  9. Return desc.
    10. -
-
- -
-

9.4.4.2 [[DefineOwnProperty]] (P, Desc)

- -

The [[DefineOwnProperty]] internal method of an arguments exotic object when called with a property name P - and Property Descriptor Desc performs - the following steps:

- -
    -
  1. Let args be the arguments object.
    2. -
  2. Let map be the value of the [[ParameterMap]] internal slot of the arguments object.
    3. -
  3. Let isMapped be HasOwnProperty(map, P).
    4. -
  4. Let allowed be OrdinaryDefineOwnProperty(args, P, - Desc).
    5. -
  5. ReturnIfAbrupt(allowed).
    6. -
  6. If allowed is false, then return false.
    7. -
  7. If the value of isMapped is not undefined, then -
      -
    1. If IsAccessorDescriptor(Desc) is true, then -
        -
      1. Call the [[Delete]] internal method of map passing P as the argument.
        2. -
      -
      2. -
    2. Else -
        -
      1. If Desc.[[Value]] is present, then -
          -
        1. Let putStatus be Put(map, P, - Desc.[[Value]], false).
          2. -
        2. Assert: putStatus is true because formal - parameters mapped by argument objects are always writable.
          3. -
        -
        2. -
      2. If Desc.[[Writable]] is present and its value is false, then -
          -
        1. Call the [[Delete]] internal method of map passing P as the argument.
          2. -
        -
        3. -
      -
      3. -
    -
    8. -
  8. Return true.
    9. -
-
- -
-

9.4.4.3 [[Get]] (P, Receiver)

- -

The [[Get]] internal method of an arguments exotic object when called with a property name P and ECMAScript language value Receiver performs the - following steps:

- -
    -
  1. Let args be the arguments object.
    2. -
  2. Let map be the value of the [[ParameterMap]] internal slot of the arguments object.
    3. -
  3. Let isMapped be HasOwnProperty(map, P).
    4. -
  4. Assert: isMapped is not an abrupt completion.
    5. -
  5. If the value of isMapped is undefined, then -
      -
    1. Let v be the result of calling the default ordinary object [[Get]] internal method (9.1.8) on args passing - P and Receiver as the arguments.
      2. -
    -
    6. -
  6. Else map contains a formal parameter mapping for P, -
      -
    1. Let v be Get(map, P).
      2. -
    -
    7. -
  7. ReturnIfAbrupt(v).
    8. -
  8. If P is "caller" and v is a strict mode Function object, throw a TypeError - exception.
    9. -
  9. Return v.
    10. -
-
- -
-

9.4.4.4 [[Set]] ( P, V, Receiver)

- -

The [[Set]] internal method of an arguments exotic object when called with property key - P, value V, and ECMAScript language value Receiver performs the following steps:

- -
    -
  1. Let args be the arguments object.
    2. -
  2. If SameValue(args, Receiver) is false, then -
      -
    1. Let isMapped be undefined.
      2. -
    -
    3. -
  3. Else, -
      -
    1. Let map be the value of the [[ParameterMap]] internal slot of the arguments object.
      2. -
    2. Let isMapped be HasOwnProperty(map, P).
      3. -
    3. Assert: isMapped is not an abrupt completion.
      4. -
    -
    4. -
  4. If the value of isMapped is undefined, then -
      -
    1. Return the result of calling the default ordinary object [[Set]] internal method (9.1.8) on args passing - P, V and Receiver as the arguments.
      2. -
    -
    5. -
  5. Else map contains a formal parameter mapping for P, -
      -
    1. Return Put(map, P, V, false).
      2. -
    -
    6. -
-
- -
-

9.4.4.5 [[Delete]] (P)

- -

The [[Delete]] internal method of an arguments exotic object when called with a property - key P performs the following steps:

- -
    -
  1. Let map be the value of the [[ParameterMap]] internal slot of the arguments object.
    2. -
  2. Let isMapped be HasOwnProperty(map, P).
    3. -
  3. Assert: isMapped is not an abrupt completion.
    4. -
  4. Let result be the result of calling the default [[Delete]] internal method for ordinary objects (9.1.10) on the arguments object passing - P as the argument.
    5. -
  5. ReturnIfAbrupt(result).
    6. -
  6. If result is true and the value of isMapped is not undefined, then -
      -
    1. Call the [[Delete]] internal method of map passing P as the argument.
      2. -
    -
    7. -
  7. Return result.
    8. -
- -
-

NOTE 1 For non-strict mode functions with simple parameter lists, those integer indexed data - properties of an arguments object whose numeric name values are less than the number of formal parameters of the - function initially share their values with the corresponding argument bindings in the function’s execution context. This means that changing the property changes the corresponding - value of the argument binding and vice-versa. This correspondence is broken if such a property is deleted and then - redefined or if the property is changed into an accessor property. For strict mode functions, the values of the - arguments object’s properties are simply a copy of the arguments passed to the function and there is no dynamic - linkage between the property values and the formal parameter values.

-
- -
-

NOTE 2 The ParameterMap object and its property values are used as a device for specifying - the arguments object correspondence to argument bindings. The ParameterMap object and the objects that are the values of - its properties are not directly accessible from ECMAScript code. An ECMAScript implementation does not need to actually - create or use such objects to implement the specified semantics.

-
- -
-

NOTE 3 Arguments objects for strict mode functions define non-configurable accessor - properties named "caller" and "callee" which throw a TypeError exception on access. The - "callee" property has a more specific meaning for non-strict mode functions and a "caller" - property has historically been provided as an implementation-defined extension by some ECMAScript implementations. The - strict mode definition of these properties exists to ensure that neither of them is defined in any other manner by - conforming ECMAScript implementations.

-
-
- -
-

9.4.4.6 CreateUnmappedArgumentsObject(argumentsList) Abstract Operation

- -

The abstract operation CreateUnmappedArgumentsObject called with an - argument argumentsList performs the following steps:

- -
    -
  1. Let len be the number of elements in argumentsList.
    2. -
  2. Let obj be ObjectCreate(%ObjectPrototype%, ([[ParameterMap]])).
    3. -
  3. Set obj’s [[ParameterMap]] internal slot - to undefined.
    4. -
  4. Perform DefinePropertyOrThrow(obj, "length", - PropertyDescriptor{[[Value]]: len, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: - true}).
    5. -
  5. Let index be 0.
    6. -
  6. Repeat while index < len, -
      -
    1. Let val be the element of argumentsList at 0-origined list position index.
      2. -
    2. Perform CreateDataProperty(obj, ToString(index), val).
      3. -
    3. Let index be index + 1
      4. -
    -
    7. -
  7. Perform DefinePropertyOrThrow(obj, @@iterator, PropertyDescriptor - {[[Value]]:%ArrayProto_values%, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: - true}).
    8. -
  8. Perform DefinePropertyOrThrow(obj, "caller", - PropertyDescriptor {[[Get]]: %ThrowTypeError%, [[Set]]: %ThrowTypeError%, [[Enumerable]]: false, [[Configurable]]: - false}).
    9. -
  9. Perform DefinePropertyOrThrow(obj, "callee", - PropertyDescriptor {[[Get]]: %ThrowTypeError%, [[Set]]: %ThrowTypeError%, [[Enumerable]]: false, [[Configurable]]: - false}).
    10. -
  10. Assert: the above property definitions will not produce an abrupt completion.
    11. -
  11. Return obj
    12. -
-
- -
-
-

9.4.4.7 CreateMappedArgumentsObject ( func, formals, argumentsList, env ) - Abstract Operation

- -

The abstract operation CreateMappedArgumentsObject is called with - object func, grammar production formals, List argumentsList, and environment record env. The following steps are performed:

- -
    -
  1. Assert: formals does not contain a rest parameter, any binding - patterns, or any initializers. It may contain duplicate identifiers.
    2. -
  2. Let len be the number of elements in argumentsList.
    3. -
  3. Let obj be a newly created arguments exotic object with a [[ParameterMap]] internal slot.
    4. -
  4. Set the [[GetOwnProperty]] internal method of obj as specified in 9.4.4.1.
    5. -
  5. Set the [[DefineOwnProperty]] internal method of obj as specified in 9.4.4.2.
    6. -
  6. Set the [[Get]] internal method of obj as specified in 9.4.4.3.
    7. -
  7. Set the [[Set]] internal method of obj as specified in 9.4.4.4.
    8. -
  8. Set the [[Delete]] internal method of obj as specified in 9.4.4.5.
    9. -
  9. Set the remainder of obj’s essential internal methods to the default ordinary object definitions - specified in 9.1.
    10. -
  10. Set the [[Prototype]] internal slot of obj to - %ObjectPrototype%.
    11. -
  11. Set the [[Extensible]] internal slot of obj - to true.
    12. -
  12. Let parameterNames be the BoundNames of formals.
    13. -
  13. Let numberOfParameters be the number of elements in parameterNames
    14. -
  14. Let index be 0.
    15. -
  15. Repeat while index < len , -
      -
    1. Let val be the element of argumentsList at 0-origined list position index.
      2. -
    2. Perform CreateDataProperty(obj, ToString(index), val).
      3. -
    3. Let index be index + 1
      4. -
    -
    16. -
  16. Perform DefinePropertyOrThrow(obj, "length", - PropertyDescriptor{[[Value]]: len, [[Writable]]: true, [[Enumerable]]: false, - [[Configurable]]: true}).
    17. -
  17. Let map be ObjectCreate(null).
    18. -
  18. Let mappedNames be an empty List.
    19. -
  19. Let index be numberOfParameters − 1.
    20. -
  20. Repeat while index ≥ 0 , -
      -
    1. Let name be the element of parameterNames at 0-origined list position index.
      2. -
    2. If name is not an element of mappedNames, then -
        -
      1. Add name as an element of the list mappedNames.
        2. -
      2. If index < len, then -
          -
        1. Let g be MakeArgGetter(name, env).
          2. -
        2. Let p be MakeArgSetter(name, env).
          3. -
        3. Call the [[DefineOwnProperty]] internal method of map passing ToString(index) and the PropertyDescriptor{[[Set]]: p, [[Get]]: - g,[[Enumerable]]: false, [[Configurable]]: true} as arguments.
          4. -
        -
        3. -
      -
      3. -
    3. Let index be index − 1
      4. -
    -
    21. -
  21. Set the [[ParameterMap]] internal slot of obj - to map.
    22. -
  22. Perform DefinePropertyOrThrow(obj, @@iterator, PropertyDescriptor - {[[Value]]:%ArrayProto_values%, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: - true}).
    23. -
  23. Perform DefinePropertyOrThrow(obj, "callee", - PropertyDescriptor {[[Value]]: func, [[Writable]]: true, [[Enumerable]]: false, - [[Configurable]]: true}).
    24. -
  24. Assert: the above property definitions will not produce an abrupt completion.
    25. -
  25. Return obj
    26. -
-
- -
-

9.4.4.7.1 MakeArgGetter ( name, env) Abstract Operation

- -

The abstract operation MakeArgGetter called with String - name and environment record env creates a built-in function object that when executed returns the - value bound for name in env. It performs the following steps:

- -
    -
  1. Let realm be the current Realm.
    2. -
  2. Let steps be the steps of a ArgGetter function as specified below.
    3. -
  3. Let getter be CreateBuiltinFunction(realm, steps, - %FunctionPrototype%, ([[name]], [[env]]) ).
    4. -
  4. Set getter’s [[name]] internal slot to - name.
    5. -
  5. Set getter’s [[env]] internal slot to - env.
    6. -
  6. Return getter.
    7. -
- -

An ArgGetter function is an anonymous built-in function with [[name]] and [[env]] internal slots. When an ArgGetter - function f that expects no arguments is called it performs the following steps:

- -
    -
  1. Let name be the value of f’s [[name]] internal slot.
    2. -
  2. Let env be the value of f’s [[env]] internal slot
    3. -
  3. Return the result of calling the GetBindingValue concrete method of env with arguments name and - false.
    4. -
- -
-

NOTE ArgGetter functions are never directly accessible to ECMAScript code.

-
-
- -
-

9.4.4.7.2 MakeArgSetter ( name, env) Abstract Operation

- -

The abstract operation MakeArgSetter called with String - name and environment record env creates a built-in function object that when executed sets the - value bound for name in env. It performs the following steps:

- -
    -
  1. Let realm be the current Realm.
    2. -
  2. Let steps be the steps of a ArgSetter function as specified below.
    3. -
  3. Let setter be CreateBuiltinFunction(realm, steps, - %FunctionPrototype%, ([[name]], [[env]]) ).
    4. -
  4. Set setter’s [[name]] internal slot to - name.
    5. -
  5. Set setter’s [[env]] internal slot to - env.
    6. -
  6. Return setter.
    7. -
- -

An ArgSetter function is an anonymous built-in function with [[name]] and [[env]] internal slots. When an ArgSetter - function f is called with argument value it performs the following steps:

- -
    -
  1. Let name be the value of f’s [[name]] internal slot.
    2. -
  2. Let env be the value of f’s [[env]] internal slot
    3. -
  3. Return the result of calling the SetMutableBinding concrete method of env with arguments name, - value, and false.
    4. -
- -
-

NOTE ArgSetter functions are never directly accessible to ECMAScript code.

-
-
-
-
- -
-
-

9.4.5 Integer Indexed Exotic Objects

- -

An Integer Indexed object is an exotic object that performs special handling of integer index property keys.

- -

Integer Indexed exotic objects have the same internal slots as ordinary objects additionally [[ViewedArrayBuffer]], - [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.

- -

Integer Indexed Exotic objects provide alternative definitions for the following internal methods. All of the other - Integer Indexed exotic object essential internal methods that are not defined below are as specified in 9.1.

-
- -
-

9.4.5.1 [[GetOwnProperty]] ( P )

- -

When the [[GetOwnProperty]] internal method of an Integer Indexed exotic object O is called with property key P the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Assert: O is an Object that has a [[ViewedArrayBuffer]] internal slot.
    3. -
  3. If Type(P) is String, then -
      -
    1. Let numericIndex be CanonicalNumericIndexString(P).
      2. -
    2. Assert: numericIndex is not an abrupt completion.
      3. -
    3. If numericIndex is not undefined, then -
        -
      1. Let value be IntegerIndexedElementGet (O, - numericIndex).
        2. -
      2. ReturnIfAbrupt(value).
        3. -
      3. If value is undefined, then return undefined.
        4. -
      4. Return a PropertyDescriptor{ [[Value]]: value, [[Enumerable]]: true, [[Writable]]: - true, [[Configurable]]: false }.
        5. -
      -
      4. -
    -
    4. -
  4. Return OrdinaryGetOwnProperty(O, P).
    5. -
-
- -
-

9.4.5.2 [[DefineOwnProperty]] ( P, Desc)

- -

When the [[DefineOwnProperty]] internal method of an Integer Indexed exotic object O is called with property key P, and Property - Descriptor Desc the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Assert: O is an Object that has a [[ViewedArrayBuffer]] internal slot.
    3. -
  3. If Type(P) is String, then -
      -
    1. If the value of O’s [[ViewedArrayBuffer]] is undefined, then throw a TypeError - exception.
      2. -
    2. Let numericIndex be CanonicalNumericIndexString - (P).
      3. -
    3. Assert: numericIndex is not an abrupt completion.
      4. -
    4. If numericIndex is not undefined, then -
        -
      1. If IsInteger(numericIndex) is false then return false
        2. -
      2. Let intIndex be numericIndex.
        3. -
      3. If intIndex = −0, then return false.
        4. -
      4. If intIndex < 0, then return false.
        5. -
      5. Let length be the value of O’s [[ArrayLength]] internal slot.
        6. -
      6. If intIndex ≥ length, then return false.
        7. -
      7. If IsAccessorDescriptor(Desc) is true, then return - false.
        8. -
      8. If Desc has a [[Configurable]] field and if Desc.[[Configurable]] is true, then return - false.
        9. -
      9. If Desc has an [[Enumerable]] field and if Desc.[[Enumerable]] is false, then return - false.
        10. -
      10. If Desc has a [[Writable]] field and if Desc.[[Writable]] is false, then return - false.
        11. -
      11. If Desc has a [[Value]] field, then -
          -
        1. Let value be Desc.[[Value]].
          2. -
        2. Let status be IntegerIndexedElementSet (O, - intIndex, value).
          3. -
        3. ReturnIfAbrupt(status).
          4. -
        -
        12. -
      12. Return true.
        13. -
      -
      5. -
    -
    4. -
  4. Return OrdinaryDefineOwnProperty(O, P, Desc).
    5. -
-
- -
-

9.4.5.3 [[Get]] (P, Receiver)

- -

When the [[Get]] internal method of an Integer Indexed exotic object O is called with property key P and ECMAScript language - value Receiver the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. If Type(P) is String and if SameValue(O, Receiver) is true, then -
      -
    1. Let numericIndex be CanonicalNumericIndexString - (P).
      2. -
    2. Assert: numericIndex is not an abrupt completion.
      3. -
    3. If numericIndex is not undefined, then -
        -
      1. Return IntegerIndexedElementGet (O, - numericIndex).
        2. -
      -
      4. -
    -
    3. -
  3. Return the result of calling the default ordinary object [[Get]] internal method (9.1.8) on O passing - P and Receiver as arguments.
    4. -
-
- -
-

9.4.5.4 [[Set]] ( P, V, Receiver)

- -

When the [[Set]] internal method of an Integer Indexed exotic object O is called with property key P, value V, and ECMAScript language value Receiver, the following steps - are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. If Type(P) is String and if SameValue(O, Receiver) is true, then -
      -
    1. Let numericIndex be CanonicalNumericIndexString - (P).
      2. -
    2. Assert: numericIndex is not an abrupt completion.
      3. -
    3. If numericIndex is not undefined, then -
        -
      1. Return ToBoolean(IntegerIndexedElementSet (O, numericIndex, - V)).
        2. -
      -
      4. -
    -
    3. -
  3. Return the result of calling the default ordinary object [[Set]] internal method (9.1.8) on O passing - P, V, and Receiver as arguments.
    4. -
-
- -
-

9.4.5.5 [[Enumerate]] ()

- -

When the [[Enumerate]] internal method of an Integer Indexed exotic object O is called the following steps - are taken:

- -
    -
  1. Let indexKeys be a new empty List.
    2. -
  2. Assert: O is an Object that has [[ViewedArrayBuffer]], - [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.
    3. -
  3. If the value of O’s [[ViewedArrayBuffer]] is undefined, then throw a TypeError - exception.
    4. -
  4. Let len be the value of O’s [[ArrayLength]] internal slot.
    5. -
  5. For each integer i starting with 0 such that i < len, in ascending order, -
      -
    1. Add ToString(i) as the last element of indexKeys.
      2. -
    -
    6. -
  6. Let ordinary be the result of calling the default ordinary object [[Enumerate]] internal method (9.1.11) on O.
    7. -
  7. ReturnIfAbrupt(ordinary).
    8. -
  8. Return CreateCompoundIterator(CreateListIterator(indexKeys), ordinary).
    9. -
-
- -
-

9.4.5.6 [[OwnPropertyKeys]] ()

- -

When the [[OwnPropertyKeys]] internal method of an Integer Indexed exotic object O is called the following - steps are taken:

- -
    -
  1. Let keys be a new empty List.
    2. -
  2. Assert: O is an Object that has [[ViewedArrayBuffer]], - [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.
    3. -
  3. If the value of O’s [[ViewedArrayBuffer]] is undefined, then throw a TypeError - exception.
    4. -
  4. Let len be the value of O’s [[ArrayLength]] internal slot.
    5. -
  5. For each integer i starting with 0 such that i < len, in ascending order, -
      -
    1. Add ToString(i) as the last element of keys.
      2. -
    -
    6. -
  6. For each own property key P of O such that P is an integer index - and ToInteger(P) ≥ len, in ascending numeric index order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    7. -
  7. For each own property key P of O such that Type(P) is String and P is not an integer index, in - property creation order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    8. -
  8. For each own property key P of O such that Type(P) is Symbol, in property creation order -
      -
    1. Add P as the last element of keys.
      2. -
    -
    9. -
  9. Return CreateArrayFromList(keys).
    10. -
-
- -
-

9.4.5.7 IntegerIndexedObjectCreate Abstract Operation

- -

The abstract operation IntegerIndexedObjectCreate with argument prototype is used to specify the creation of - new Integer Indexed exotic objects. It performs the following steps:

- -
    -
  1. Let A be a newly created object.
    2. -
  2. Set A’s essential internal methods to the default ordinary object definitions specified in 9.1.
    3. -
  3. Set the [[GetOwnProperty]] internal method of A as specified in 9.4.5.1.
    4. -
  4. Set the [[DefineOwnProperty]] internal method of A as specified in 9.4.5.2.
    5. -
  5. Set the [[Get]] internal method of A as specified in 9.4.5.3.
    6. -
  6. Set the [[Set]] internal method of A as specified in 9.4.5.4.
    7. -
  7. Set the [[Enumerate]] internal method of A as specified in 9.4.5.5.
    8. -
  8. Set the [[OwnPropertyKeys]] internal method of A as specified in 9.4.5.6.
    9. -
  9. Set the [[Prototype]] internal slot of A to - prototype.
    10. -
  10. Set the [[Extensible]] internal slot of A to - true.
    11. -
  11. Return A.
    12. -
-
- -
-

9.4.5.8 IntegerIndexedElementGet ( O, index ) Abstract Operation

- -

The abstract operation IntegerIndexedElementGet with arguments O and index performs the following - steps:

- -
    -
  1. Assert: Type(index) is Number.
    2. -
  2. Assert: O is an Object that has [[ViewedArrayBuffer]], - [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.
    3. -
  3. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    4. -
  4. If buffer is undefined, then throw a TypeError exception.
    5. -
  5. If IsInteger(index) is false then return undefined
    6. -
  6. If index = −0, then return undefined.
    7. -
  7. Let length be the value of O’s [[ArrayLength]] internal slot.
    8. -
  8. If index < 0 or index ≥ length, then return undefined.
    9. -
  9. Let offset be the value of O’s [[ByteOffset]] internal slot.
    10. -
  10. Let arrayTypeName be the string value of O’s [[TypedArrayName]] internal slot.
    11. -
  11. Let elementSize be the Number value of the Element Size value specified in Table 44 - for arrayTypeName.
    12. -
  12. Let indexedPosition = (index × elementSize) + offset.
    13. -
  13. Let elementType be the string value of the Element Type value in Table 44 for - arrayTypeName.
    14. -
  14. Return GetValueFromBuffer(buffer, indexedPosition, - elementType).
    15. -
-
- -
-

9.4.5.9 IntegerIndexedElementSet ( O, index, value ) Abstract Operation

- -

The abstract operation IntegerIndexedElementSet with arguments O, index, and value - performs the following steps:

- -
    -
  1. Assert: Type(index) is Number.
    2. -
  2. Assert: O is an Object that has [[ViewedArrayBuffer]], - [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.
    3. -
  3. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    4. -
  4. If buffer is undefined, then throw a TypeError exception.
    5. -
  5. If IsInteger(index) is false then return false
    6. -
  6. If index = −0, then return undefined.
    7. -
  7. Let length be the value of O’s [[ArrayLength]] internal slot.
    8. -
  8. Let numValue be ToNumber(value).
    9. -
  9. ReturnIfAbrupt(numValue).
    10. -
  10. If index < 0 or index ≥ length, then return false.
    11. -
  11. Let offset be the value of O’s [[ByteOffset]] internal slot.
    12. -
  12. Let arrayTypeName be the string value of O’s [[TypedArrayName]] internal slot.
    13. -
  13. Let elementSize be the Number value of the Element Size value specified in Table 44 - for arrayTypeName.
    14. -
  14. Let indexedPosition = (index × elementSize) + offset.
    15. -
  15. Let elementType be the string value of the Element Type value in Table 44 for - arrayTypeName.
    16. -
  16. Let status be SetValueInBuffer(buffer, indexedPosition, - elementType, numValue).
    17. -
  17. ReturnIfAbrupt(status).
    18. -
  18. Return true.
    19. -
-
-
- -
-
-

9.4.6 - Module Exotic Objects

- -

A module object is an exotic object that exposes the bindings exported from an ECMAScript Module (See 15.1.9). There is a one-to-one - correspondence between the own properties of a module exotic object and the ExportedBindings of the Module. Each own property name is the StringValue of the corresponding exported binding. These are the - only properties of a module exotic object. Each such property has the attributes {[[Configurable]]: false, [[Enumerable]]: true}. Module objects are not extensible.

- -

Module objects have the internal slots defined in Table 28.

- -
-
Table 28 — Internal Slots of Module Exotic Objects
- - - - - - - - - - - - - - - - -
Internal SlotTypeDescription
[[ModuleEnvironment]]EnvironmentThe Declarative Environment Record that contains all of the declared top-level bindings for the corresponding module.
[[Exports]]List of StringA List containing the bound names exposed as own properties of this object. The list is ordered as if an Array of the same values had been sorted using Array.prototype.sort using SortCompare as comparefn.
-
- -

Module exotic objects provide alternative definitions for all of the internal methods.

-
- -
-

9.4.6.1 [[GetPrototypeOf]] ( )

- -

When the [[GetPrototypeOf]] internal method of a module exotic object O is called the following steps are - taken:

- -
    -
  1. Return null.
    2. -
-
- -
-

9.4.6.2 [[SetPrototypeOf]] (V)

- -

When the [[SetPrototypeOf]] internal method of a module exotic object O is called with argument V the - following steps are taken:

- -
    -
  1. Assert: Either Type(V) is Object or Type(V) is Null.
    2. -
  2. Return false.
    3. -
-
- -
-

9.4.6.3 [[IsExtensible]] ( )

- -

When the [[IsExtensible]] internal method of a module exotic object O is called the following steps are - taken:

- -
    -
  1. Return false.
    2. -
-
- -
-

9.4.6.4 [[PreventExtensions]] ( )

- -

When the [[PreventExtensions]] internal method of a module exotic object O is called the following steps are - taken:

- -
    -
  1. Return true.
    2. -
-
- -
-

9.4.6.5 [[GetOwnProperty]] (P)

- -

When the [[GetOwnProperty]] internal method of a module exotic object O is called with property key P, the following steps are taken:

- -
    -
  1. Throw a TypeError exception.
    2. -
-
- -
-

9.4.6.6 [[DefineOwnProperty]] (P, Desc)

- -

When the [[DefineOwnProperty]] internal method of a module exotic object O is called with property key P and Property - Descriptor Desc, the following steps are taken:

- -
    -
  1. Return false.
    2. -
-
- -
-

9.4.6.7 [[HasProperty]] (P)

- -

When the [[HasProperty]] internal method of a module exotic object O is called with property key P, the following steps are taken:

- -
    -
  1. Let exports be the value of O’s [[Exports]] internal slot.
    2. -
  2. If P is an element of exports, then return true.
    3. -
  3. Return false.
    4. -
-
- -
-

9.4.6.8 [[Get]] (P, Receiver)

- -

When the [[Get]] internal method of a module exotic object O is called with property key P and ECMAScript language - value Receiver the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let exports be the value of O’s [[Exports]] internal slot.
    3. -
  3. If P is not an element of exports, then return undefined.
    4. -
  4. Let env be the value of O’s [[ModuleEnvironment]] internal slot.
    5. -
  5. Return the result of calling the GetBindingValue concrete method of env with arguments P and - true.
    6. -
- -
-

NOTE Attempting to [[Get]] the value of a module export that has not yet been initialized - will throw a ReferenceError exception.

-
-
- -
-

9.4.6.9 [[Set]] ( P, V, Receiver)

- -

When the [[Set]] internal method of a module exotic object - O is called with property key P, value V, and ECMAScript language value Receiver, the following steps - are taken:

- -
    -
  1. Return false.
    2. -
-
- -
-

9.4.6.10 [[Delete]] (P)

- -

When the [[Delete]] internal method of a module exotic object O is called with property key P the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let exports be the value of O’s [[Exports]] internal slot.
    3. -
  3. If P is an element of exports, then return false.
    4. -
  4. Return true.
    5. -
-
- -
-

9.4.6.11 [[Enumerate]] ()

- -

When the [[Enumerate]] internal method of a module exotic object O is called the following steps are - taken:

- -
    -
  1. Let exports be the value of O’s [[Exports]] internal slot.
    2. -
  2. Return CreateListIterator(exports).
    3. -
-
- -
-

9.4.6.12 [[OwnPropertyKeys]] ( )

- -

When the [[OwnPropertyKeys]] internal method of a module exotic object O is called the following steps are - taken:

- -
    -
  1. Let exports be the value of O’s [[Exports]] internal slot.
    2. -
  2. Return CreateArrayFromList (exports).
    3. -
-
- -
-

9.4.6.13 ModuleObjectCreate (environment, exports)

-
    -
  1. Assert: environment is a Declarative Environment Record.
    2. -
  2. Assert: exports is a List of string values.
    3. -
  3. Let M be a newly created object.
    4. -
  4. Set M’s essential internal methods to the definitions specified in 9.4.6.
    5. -
  5. Set M’s [[ModuleEnvironment]] internal - slot to environment.
    6. -
  6. Set M’s [[Exports]] internal slot to - exports.
    7. -
  7. Return M.
    8. -
-
-
-
- -
-
-

9.5 Proxy Object Internal Methods and Internal Slots

- -

A proxy object is an exotic object whose essential internal methods are partially implemented using ECMAScript code. - Every proxy objects has an internal slot called - [[ProxyHandler]]. The value of [[ProxyHandler]] is always an object, called the proxy’s handler object. - Methods of a handler object may be used to augment the implementation for one or more of the proxy object’s internal - methods. Every proxy object also has an internal slot called - [[ProxyTarget]] whose value is either an object or the null value. This object is called the proxy’s target - object.

- -

When a handler method is called to provide the implementation of a proxy object internal method, the handler method is - passed the proxy’s target object as a parameter. A proxy’s handler object does not necessarily have a method - corresponding to every essential internal method. Invoking an internal method on the proxy results in the invocation of the - corresponding internal method on the proxy’s target object if the handler object does not have a method corresponding - to the internal trap.

- -

The [[ProxyHandler]] and [[ProxyTarget]] internal slots of a proxy object are always initialized when the object is - created and typically may not be modified. Some proxy objects are created in a manner that permits them to be subsequently - revoked. When a proxy is revoked, its [[ProxyHander]] and [[ProxyTarget]] internal slots are set to null - causing subsequent invocations of internal methods on that proxy obeject to throw a TypeError - exception.

- -

Because proxy permit arbitrary ECMAScript code to be used to in the implementation of internal methods, it is possible to - define a proxy object whose handler methods violates the invariants defined in 6.1.7.3. Some of the internal method invariants defined in 6.1.7.3 are essential integrity invariants. These invariants - are explicitly enforced by the proxy internal methods specified in this section. An ECMAScript implementation must be robust - in the presence of all possible invariant violations.

- -

In the following algorithm descriptions, assume O is an ECMAScript proxy object, P is a property key value, V is any ECMAScript - language value, Desc is a Property Descriptor record, and B is a Boolean flag.

-
- -
-

9.5.1 [[GetPrototypeOf]] ( )

- -

When the [[GetPrototypeOf]] internal method of an exotic Proxy object O is called the following steps are - taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "getPrototypeOf").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[GetPrototypeOf]] internal method of target.
      2. -
    -
    7. -
  7. Let handlerProto be the result of calling the [[Call]] internal method of trap with handler as - the this value and a new List containing - target.
    8. -
  8. ReturnIfAbrupt(handlerProto).
    9. -
  9. If Type(handlerProto) is neither Object nor Null, then - throw a TypeError exception.
    10. -
  10. Let extensibleTarget be IsExtensible(target).
    11. -
  11. ReturnIfAbrupt(extensibleTarget).
    12. -
  12. If extensibleTarget is true, then return handlerProto.
    13. -
  13. Let targetProto be the result of calling the [[GetPrototypeOf]] internal method of target.
    14. -
  14. ReturnIfAbrupt(targetProto).
    15. -
  15. If SameValue(handlerProto, targetProto) is false, then throw a - TypeError exception.
    16. -
  16. Return handlerProto.
    17. -
- -
-

NOTE [[GetPrototypeOf]] for proxy objects enforces the following invariant:

- -
    -
  • -

    The result of [[GetPrototypeOf]] must be either an Object or null.

    -
    • - -
  • -

    If the target object is not extensible, [[GetPrototypeOf]] applied to the proxy object must return the same value - as [[GetPrototypeOf] applied to the proxy object’s target object.

    -
    • -
-
-
- -
-

9.5.2 [[SetPrototypeOf]] (V)

- -

When the [[SetPrototypeOf]] internal method of an exotic Proxy object O is called with argument V the - following steps are taken:

- -
    -
  1. Assert: Either Type(V) is Object or Type(V) is Null.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "setPrototypeOf").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[SetPrototypeOf]] internal method of target with argument V.
      2. -
    -
    8. -
  8. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target and - V.
    9. -
  9. Let booleanTrapResult be ToBoolean(trapResult).
    10. -
  10. ReturnIfAbrupt(booleanTrapResult).
    11. -
  11. Let extensibleTarget be IsExtensible(target).
    12. -
  12. ReturnIfAbrupt(extensibleTarget).
    13. -
  13. If extensibleTarget is true, then return booleanTrapResult.
    14. -
  14. Let targetProto be the result of calling the [[GetPrototypeOf]] internal method of target.
    15. -
  15. ReturnIfAbrupt(targetProto).
    16. -
  16. If booleanTrapResult is true and SameValue(V, targetProto) is - false, then throw a TypeError exception.
    17. -
  17. Return booleanTrapResult.
    18. -
- -
-

NOTE [[SetPrototypeOf]] for proxy objects enforces the following invariant:

- -
    -
  • -

    If the target object is not extensible, the argument value must be the same as the result of [[GetPrototypeOf]] - applied to target object.

    -
    • -
-
-
- -
-

9.5.3 [[IsExtensible]] ( )

- -

When the [[IsExtensible]] internal method of an exotic Proxy object O is called the following steps are - taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "isExtensible").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[IsExtensible]] internal method of target.
      2. -
    -
    7. -
  7. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target.
    8. -
  8. Let booleanTrapResult be ToBoolean(trapResult).
    9. -
  9. ReturnIfAbrupt(booleanTrapResult).
    10. -
  10. Let targetResult be the result of calling the [[IsExtensible]] internal method of target.
    11. -
  11. ReturnIfAbrupt(targetResult).
    12. -
  12. If SameValue(booleanTrapResult, targetResult) is false, then throw a - TypeError exception.
    13. -
  13. Return booleanTrapResult.
    14. -
- -
-

NOTE [[IsExtensible]] for proxy objects enforces the following invariant:

- -
    -
  • -

    [[IsExtensible]] applied to the proxy object must return the same value as [[IsExtensible]] applied to the proxy - object’s target object with the same argument.

    -
    • -
-
-
- -
-

9.5.4 [[PreventExtensions]] ( )

- -

When the [[PreventExtensions]] internal method of an exotic Proxy object O is called the following steps are - taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "preventExtensions").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[PreventExtensions]] internal method of target.
      2. -
    -
    7. -
  7. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target.
    8. -
  8. Let booleanTrapResult be ToBoolean(trapResult)
    9. -
  9. ReturnIfAbrupt(booleanTrapResult).
    10. -
  10. If booleanTrapResult is true, then -
      -
    1. Let targetIsExtensible be the result of calling the [[IsExtensible]] internal method of target.
      2. -
    2. ReturnIfAbrupt(targetIsExtensible).
      3. -
    3. If targetIsExtensible is true, then throw a TypeError exception.
      4. -
    -
    11. -
  11. Return booleanTrapResult.
    12. -
- -
-

NOTE [[PreventExtensions]] for proxy objects enforces the following invariant:

- -
    -
  • -

    [[PreventExtensions]] applied to the proxy object only returns true if [[IsExtensible]] applied to the proxy - object’s target object is false.

    -
    • -
-
-
- -
-

9.5.5 [[GetOwnProperty]] (P)

- -

When the [[GetOwnProperty]] internal method of an exotic Proxy object O is called with property key P, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, - "getOwnPropertyDescriptor").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[GetOwnProperty]] internal method of target with argument P.
      2. -
    -
    8. -
  8. Let trapResultObj be the result of calling the [[Call]] internal method of trap with handler as - the this value and a new List containing target - and P.
    9. -
  9. ReturnIfAbrupt(trapResultObj).
    10. -
  10. If Type(trapResultObj) is neither Object nor Undefined, - then throw a TypeError exception.
    11. -
  11. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with argument - P.
    12. -
  12. ReturnIfAbrupt(targetDesc).
    13. -
  13. If trapResultObj is undefined, then -
      -
    1. If targetDesc is undefined, then return undefined.
      2. -
    2. If targetDesc.[[Configurable]] is false, then throw a TypeError exception.
      3. -
    3. Let extensibleTarget be IsExtensible(target).
      4. -
    4. ReturnIfAbrupt(extensibleTarget).
      5. -
    5. If ToBoolean(extensibleTarget) is false, then throw a TypeError - exception.
      6. -
    6. Return undefined.
      7. -
    -
    14. -
  14. Let extensibleTarget be IsExtensible(target).
    15. -
  15. ReturnIfAbrupt(extensibleTarget).
    16. -
  16. Let resultDesc be ToPropertyDescriptor(trapResultObj).
    17. -
  17. ReturnIfAbrupt(resultDesc).
    18. -
  18. Call CompletePropertyDescriptor(resultDesc, - undefined).
    19. -
  19. Let valid be IsCompatiblePropertyDescriptor - (extensibleTarget, resultDesc, targetDesc).
    20. -
  20. If valid is false, then throw a TypeError exception.
    21. -
  21. If resultDesc.[[Configurable]] is false, then -
      -
    1. If targetDesc is undefined or targetDesc.[[Configurable]] is true, then -
        -
      1. Throw a TypeError exception.
        2. -
      -
      2. -
    -
    22. -
  22. Return resultDesc.
    23. -
- -
-

NOTE [[GetOwnProperty]] for proxy objects enforces the following invariants:

- -
    -
  • -

    The result of [[GetOwnProperty]] must be either an Object or undefined.

    -
    • - -
  • -

    A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target - object.

    -
    • - -
  • -

    A property cannot be reported as non-existent, if it exists as an own property of the target object and the target - object is not extensible.

    -
    • - -
  • -

    A property cannot be reported as existent, if it does not exists as an own property of the target object and the - target object is not extensible.

    -
    • - -
  • -

    A property cannot be reported as non-configurable, if it does not exists as an own property of the target object or - if it exists as a configurable own property of the target object.

    -
    • - -
  • -

    The result of [[GetOwnProperty]] can be applied to the target object using [[DefineOwnProperty]] and will not throw - an exception.

    -
    • -
-
-
- -
-

9.5.6 [[DefineOwnProperty]] (P, Desc)

- -

When the [[DefineOwnProperty]] internal method of an exotic Proxy object O is called with property key P and Property - Descriptor Desc, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "defineProperty").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[DefineOwnProperty]] internal method of target with arguments P - and Desc.
      2. -
    -
    8. -
  8. Let descObj be FromPropertyDescriptor(Desc).
    9. -
  9. NOTE If Desc was originally generated from an object using ToPropertyDescriptor, then descObj will be that original object.
    10. -
  10. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target, - P, and descObj.
    11. -
  11. Let booleanTrapResult be ToBoolean(trapResult).
    12. -
  12. ReturnIfAbrupt(booleanTrapResult).
    13. -
  13. If booleanTrapResult is false, then return false.
    14. -
  14. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with argument - P.
    15. -
  15. ReturnIfAbrupt(targetDesc).
    16. -
  16. Let extensibleTarget be IsExtensible(target).
    17. -
  17. ReturnIfAbrupt(extensibleTarget).
    18. -
  18. If Desc has a [[Configurable]] field and if Desc.[[Configurable]] is false, then -
      -
    1. Let settingConfigFalse be true.
      2. -
    -
    19. -
  19. Else let settingConfigFalse be false.
    20. -
  20. If targetDesc is undefined, then -
      -
    1. If extensibleTarget is false, then throw a TypeError exception.
      2. -
    2. If settingConfigFalse is true, then throw a TypeError exception.
      3. -
    -
    21. -
  21. Else targetDesc is not undefined, -
      -
    1. If IsCompatiblePropertyDescriptor(extensibleTarget, - Desc , targetDesc) is false, then throw a TypeError exception.
      2. -
    2. If settingConfigFalse is true and targetDesc.[[Configurable]] is true, then throw a - TypeError exception.
      3. -
    -
    22. -
  22. Return true.
    23. -
- -
-

NOTE [[DefineOwnProperty]] for proxy objects enforces the following invariants:

- -
    -
  • -

    A property cannot be added, if the target object is not extensible.

    -
    • - -
  • -

    A property cannot be added as or modified to be non-configurable, if it does not exists as a non-configurable own - property of the target object.

    -
    • - -
  • -

    A property may not be non-configurable, if is corresponding configurable property of the target object exists.

    -
    • - -
  • -

    If a property has a corresponding target object property then apply the Property Descriptor of the property to the target object using - [[DefineOwnProperty]] will not throw an exception.

    -
    • -
-
-
- -
-

9.5.7 [[HasProperty]] (P)

- -

When the [[HasProperty]] internal method of an exotic Proxy object O is called with property key P, the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "has").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[HasProperty]] internal method of target with argument P.
      2. -
    -
    8. -
  8. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target and - P.
    9. -
  9. Let booleanTrapResult be ToBoolean(trapResult).
    10. -
  10. ReturnIfAbrupt(booleanTrapResult).
    11. -
  11. If booleanTrapResult is false, then -
      -
    1. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with - argument P.
      2. -
    2. ReturnIfAbrupt(targetDesc).
      3. -
    3. If targetDesc is not undefined, then -
        -
      1. If targetDesc.[[Configurable]] is false, then throw a TypeError exception.
        2. -
      2. Let extensibleTarget be IsExtensible(target).
        3. -
      3. ReturnIfAbrupt(extensibleTarget).
        4. -
      4. If extensibleTarget is false, then throw a TypeError exception.
        5. -
      -
      4. -
    -
    12. -
  12. Return booleanTrapResult.
    13. -
- -
-

NOTE [[HasProperty]] for proxy objects enforces the following invariants:

- -
    -
  • -

    A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target - object.

    -
    • - -
  • -

    A property cannot be reported as non-existent, if it exists as an own property of the target object and the target - object is not extensible.

    -
    • -
-
-
- -
-

9.5.8 [[Get]] (P, Receiver)

- -

When the [[Get]] internal method of an exotic Proxy object O is called with property key P and ECMAScript language - value Receiver the following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "get").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[Get]] internal method of target with arguments P and - Receiver.
      2. -
    -
    8. -
  8. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target, - P, and Receiver.
    9. -
  9. ReturnIfAbrupt(trapResult).
    10. -
  10. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with argument - P.
    11. -
  11. ReturnIfAbrupt(targetDesc).
    12. -
  12. If targetDesc is not undefined, then -
      -
    1. If IsDataDescriptor(targetDesc) and targetDesc.[[Configurable]] - is false and targetDesc.[[Writable]] is false, then -
        -
      1. If SameValue(trapResult, targetDesc.[[Value]]) is false, - then throw a TypeError exception.
        2. -
      -
      2. -
    2. If IsAccessorDescriptor(targetDesc) and - targetDesc.[[Configurable]] is false and targetDesc.[[Get]] is undefined, then -
        -
      1. If trapResult is not undefined, then throw a TypeError exception.
        2. -
      -
      3. -
    -
    13. -
  13. Return trapResult.
    14. -
- -
-

NOTE [[Get]] for proxy objects enforces the following invariants:

- -
    -
  • -

    The value reported for a property must be the same as the value of the corresponding target object property if the - target object property is a non-writable, non-configurable data property.

    -
    • - -
  • -

    The value reported for a property must be undefined if the corresponding corresponding target object - property is non-configurable accessor property that has undefined as its [[Get]] attribute.

    -
    • -
-
-
- -
-

9.5.9 [[Set]] ( P, V, Receiver)

- -

When the [[Set]] internal method of an exotic Proxy object O is called with property key P, value V, and ECMAScript language value Receiver, the following steps - are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "set").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[Set]] internal method of target with arguments P, V, and - Receiver.
      2. -
    -
    8. -
  8. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target, - P, V, and Receiver.
    9. -
  9. Let booleanTrapResult be ToBoolean(trapResult).
    10. -
  10. ReturnIfAbrupt(booleanTrapResult).
    11. -
  11. If booleanTrapResult is false, then return false.
    12. -
  12. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with argument - P.
    13. -
  13. ReturnIfAbrupt(targetDesc).
    14. -
  14. If targetDesc is not undefined, then -
      -
    1. If IsDataDescriptor(targetDesc) and targetDesc.[[Configurable]] - is false and targetDesc.[[Writable]] is false, then -
        -
      1. If SameValue(V, targetDesc.[[Value]]) is false, then throw a - TypeError exception.
        2. -
      -
      2. -
    2. If IsAccessorDescriptor(targetDesc) and - targetDesc.[[Configurable]] is false, then -
        -
      1. If targetDesc.[[Set]] is undefined, then throw a TypeError exception.
        2. -
      -
      3. -
    -
    15. -
  15. Return true.
    16. -
- -
-

NOTE [[Set]] for proxy objects enforces the following invariants:

- -
    -
  • -

    Cannnot change the value of a property to be different from the value of the corresponding target object property - if the corresponding target object property is a non-writable, non-configurable data property.

    -
    • - -
  • -

    Cannot set the value of a property if the corresponding corresponding target object property is a non-configurable - accessor property that has undefined as its [[Set]] attribute.

    -
    • -
-
-
- -
-

9.5.10 [[Delete]] (P)

- -

When the [[Delete]] internal method of an exotic Proxy object O is called with property name P the - following steps are taken:

- -
    -
  1. Assert: IsPropertyKey(P) is - true.
    2. -
  2. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    3. -
  3. If handler is null, then throw a TypeError exception.
    4. -
  4. Let target be the value of the [[ProxyTarget]] internal slot of O.
    5. -
  5. Let trap be GetMethod(handler, "deleteProperty").
    6. -
  6. ReturnIfAbrupt(trap).
    7. -
  7. If trap is undefined, then -
      -
    1. Return the result of calling the [[Delete]] internal method of target with argument P.
      2. -
    -
    8. -
  8. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target and - P.
    9. -
  9. Let booleanTrapResult be ToBoolean(trapResult).
    10. -
  10. ReturnIfAbrupt(booleanTrapResult).
    11. -
  11. If booleanTrapResult is false, then return false.
    12. -
  12. Let targetDesc be the result of calling the [[GetOwnProperty]] internal method of target with argument - P.
    13. -
  13. ReturnIfAbrupt(targetDesc).
    14. -
  14. If targetDesc is undefined, then return true.
    15. -
  15. If targetDesc.[[Configurable]] is false, then throw a TypeError exception.
    16. -
  16. Return true.
    17. -
- -
-

NOTE [[Delete]] for proxy objects enforces the following invariant:

- -
    -
  • -

    A property cannot be deleted, if it exists as a non-configurable own property of the target object.

    -
    • -
-
-
- -
-

9.5.11 [[Enumerate]] ()

- -

When the [[Enumerate]] internal method of an exotic Proxy object O is called the following steps are - taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "enumerate").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[Enumerate]] internal method of target.
      2. -
    -
    7. -
  7. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target.
    8. -
  8. ReturnIfAbrupt(trapResult).
    9. -
  9. If Type(trapResult) is not Object, then throw a - TypeError exception.
    10. -
  10. Return trapResult.
    11. -
- -
-

NOTE [[Enumerate]] for proxy objects enforces the following invariants:

- -
    -
  • The result of [[Enumerate]] must be an Object.
    • -
-
-
- -
-

9.5.12 [[OwnPropertyKeys]] ( )

- -

When the [[OwnPropertyKeys]] internal method of an exotic Proxy object O is called the following steps are - taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "ownKeys").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[OwnPropertyKeys]] internal method of target.
      2. -
    -
    7. -
  7. Let trapResult be the result of calling the [[Call]] internal method of trap with handler as the - this value and a new List containing target.
    8. -
  8. ReturnIfAbrupt(trapResult).
    9. -
  9. If Type(trapResult) is not Object, then throw a - TypeError exception.
    10. -
  10. TODO: we may need to add a lot of additional invariant checking here according to the wiki spec. But maybe it really - isn’t necessary
    11. -
  11. Return trapResult.
    12. -
- -
-

NOTE [[OwnPropertyKeys]] for proxy objects enforces the following invariants:

- -
    -
  • The result of [[OwnPropertyKeys]] must be an Object.
    • -
-
-
- -
-

9.5.13 [[Call]] (thisArgument, argumentsList)

- -

The [[Call]] internal method of an exotic Proxy object O is called with parameters thisArgument and - argumentsList, a List of ECMAScript language values. The following steps are taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "apply").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. Return the result of calling the [[Call]] internal method of target with arguments thisArgument and - argumentsList.
      2. -
    -
    7. -
  7. Let argArray be CreateArrayFromList(argumentsList).
    8. -
  8. Return the result of calling the [[Call]] internal method of trap with handler as the this value - and a new List containing target, thisArgument, - and argArray.
    9. -
- -
-

NOTE A Proxy exotic object only has a [[Call]] internal method if the initial value of its - [[ProxyTarget]] internal slot is an object that has a - [[Call]] internal method.

-
-
- -
-

9.5.14 [[Construct]] Internal Method

- -

The [[Construct]] internal method of an exotic Proxy object O is called with a single parameter - argumentsList which is a possibly empty List of ECMAScript language values. The following steps are taken:

- -
    -
  1. Let handler be the value of the [[ProxyHandler]] internal slot of O.
    2. -
  2. If handler is null, then throw a TypeError exception.
    3. -
  3. Let target be the value of the [[ProxyTarget]] internal slot of O.
    4. -
  4. Let trap be GetMethod(handler, "construct").
    5. -
  5. ReturnIfAbrupt(trap).
    6. -
  6. If trap is undefined, then -
      -
    1. If target does not have a [[Construct]] internal method, then throw a TypeError exception.
      2. -
    2. Return the result of calling the [[Construct]] internal method of target with argument - argumentsList.
      3. -
    -
    7. -
  7. Let argArray be CreateArrayFromList(argumentsList).
    8. -
  8. Let newObj be the result of calling trap with handler as the this value and a new List containing target and argArray.
    9. -
  9. ReturnIfAbrupt(newObj).
    10. -
  10. If Type(newObj) is not Object, then throw a - TypeError exception.
    11. -
  11. Return newObj.
    12. -
- -
-

NOTE 1 A Proxy exotic object only has a [[Construct]] internal method if the initial value of - its [[ProxyTarget]] internal slot is an object that has a - [[Construct]] internal method.

-
- -
-

NOTE 2 [[Construct]]] for proxy objects enforces the following invariants:

- -
    -
  • The result of [[Construct]] must be an Object.
    • -
-
-
- -
-

9.5.15 - ProxyCreate(target, handler) Abstract Operation

- -

The abstract operation ProxyCreate with arguments target and handler is used to specify the - creation of new Proxy exotic objects. It performs the following steps:

- -
    -
  1. If Type(target) is not Object, throw a TypeError - Exception.
    2. -
  2. If Type(handler) is not Object, throw a TypeError - Exception.
    3. -
  3. Let P be a newly created object.
    4. -
  4. Set P’s essential internal methods to the definitions specified in 9.5.
    5. -
  5. If IsCallable(target) is true, then -
      -
    1. Set the [[Call]] internal method of P as specified in 9.5.13.
      2. -
    2. If target has a [[Construct]] internal method, then -
        -
      1. Set the [[Construct]] internal method of P as specified in 9.5.14.
        2. -
      -
      3. -
    -
    6. -
  6. Set the [[ProxyTarget]] internal slot of P to - target.
    7. -
  7. Set the [[ProxyHandler]] internal slot of P to - handler.
    8. -
  8. Return P.
    9. -
-
-
-
- -
-
-

10 - ECMAScript Language: Source Code

-
- -
-
-

10.1 Source - Text

-

Syntax

- -
-
SourceCharacter ::
-
any Unicode code point
-
- -

The ECMAScript code is expressed using Unicode, version 5.1 or later. ECMAScript source text is a sequence of code - points. All Unicode code point values from U+0000 to U+10FFFF, including surrogate code points, may occur in source text - where permitted by the ECMAScript grammars. The actual encodings used to store and interchange ECMAScript source text is not - relevant to this specification. Regardless of the external source text encoding, a conforming ECMAScript implementation - processes the source text as if it was an equivalent sequence of SourceCharacter values. Each SourceCharacter being a Unicode code point. Conforming ECMAScript implementations are not required to - perform any normalisation of text, or behave as though they were performing normalisation of text.

- -

The components of a combining character sequence are treated as individual Unicode code points even though a user might - think of the whole sequence as a single character.

- -
-

NOTE In string literals, regular expression literals, template literals and identifiers, any - Unicode code point may also be expressed using Unicode escape sequences that explicitly express a code point’s - numeric value. Within a comment, such an escape sequence is effectively ignored as part of the comment.

- -

ECMAScript differs from the Java programming language in the behaviour of Unicode escape sequences. In a Java program, - if the Unicode escape sequence \u000A, for example, occurs within a single-line comment, it is interpreted as - a line terminator (Unicode character 000A is line feed) and therefore the next character is not part of the - comment. Similarly, if the Unicode escape sequence \u000A occurs within a string literal in a Java program, - it is likewise interpreted as a line terminator, which is not allowed within a string literal—one must write - \n instead of \u000A to cause a line feed to be part of the string value of a string literal. In - an ECMAScript program, a Unicode escape sequence occurring within a comment is never interpreted and therefore cannot - contribute to termination of the comment. Similarly, a Unicode escape sequence occurring within a string literal in an - ECMAScript program always contributes a Unicode code unit or code point (depending upon the first of the escape) to the - literal and is never interpreted as a line terminator or as a quote mark that might terminate the string literal.

-
-
- -
-

10.1.1 Static Semantics: UTF-16Encoding

- -

The UTF-16Encoding of a numeric code point value, cp, is determined as follows:

- -
    -
  1. Assert: 0 ≤ cp ≤ 0x10FFFF.
    2. -
  2. If cp ≤ 65535, then return cp.
    3. -
  3. Let cu1 be floor((cp – 65536) / 1024) + 0xD800.
    4. -
  4. Let cu2 be ((cp – 65536) modulo 1024) + 0xDC00.
    5. -
  5. Return the code unit sequence consisting of cu1 followed by cu2.
    6. -
-
- -
-

10.1.2 Static - Semantics: UTF16Decode(lead, trail)

- -

Two code units, lead and trail, that form a UTF-16 surrogate pair are converted to a code point by - performing the following steps:

- -
    -
  1. Assert: 0xD800 ≤ lead ≤ 0xDBFF and 0xDC00 ≤ trail ≤ - 0xDFFF.
    2. -
  2. Let cp be (lead–0xD800)×1024+( trail–0xDC00)+0x10000..
    3. -
  3. Return the code point cp.
    4. -
-
-
- -
-
-

10.2 - Types of Source Code

- -

There are four types of ECMAScript code:

- -
    -
  • -

    Global code is source text that is treated as an ECMAScript Script. The global code of a particular - Script does not include any source text that is parsed as part of a FunctionBody, GeneratorBody, - ConciseBody, ClassBody, or ModuleBody.

    -
    • - -
  • -

    Eval code is the source text supplied to the built-in eval function. More precisely, if the - parameter to the built-in eval function is a String, it is treated as an ECMAScript Script. The eval - code for a particular invocation of eval is the global code portion of that Script.

    -
    • - -
  • -

    Function code is source text that is parsed to supply the value of the [[Code]] internal slot (see 9.1.14) of function and generator objects. It includes the code that - defines and initializes the formal parameters of the function. The function code of a particular function or - generator does not include any source text that is parsed as the function code of a nested FunctionBody, - GeneratorBody, ConciseBody, or ClassBody.

    -
    • - -
  • -

    Module code is source text that is code that is provided as a ModuleBody. It is the code that is - directly evaluated when a module is initialized. The module code of a particular module does not include any source text - that is parsed as part of a nested FunctionBody, GeneratorBody, ConciseBody, ClassBody, or - ModuleBody.

    -
    • -
- -
-

NOTE Function code is generally provided as the bodies of Function Definitions (14.1), Arrow Function Definitions (14.2), Method Definitions (14.3) and - Generator Definitions (14.4). Function code is also derived from the - last argument to the Function constructor (19.2.1.1) and the GeneratorFunction - constructor (25.2.1.1).

-
-
- -
-

10.2.1 - Strict Mode Code

- -

An ECMAScript Script syntactic unit may be processed using either unrestricted or strict mode - syntax and semantics. When processed using strict mode the four types of ECMAScript code are referred to as module code, - strict global code, strict eval code, and strict function code. Code is interpreted as strict mode code in the following - situations:

- -
    -
  • -

    Global code is strict global code if it begins with a Directive Prologue that contains a Use Strict Directive (see 14.1.1).

    -
    • - -
  • -

    Module code is always strict code.

    -
    • - -
  • -

    All parts of a ClassDeclaration or a ClassExpression are strict - code.

    -
    • - -
  • -

    Eval code is strict eval code if it begins with a Directive Prologue that contains a Use Strict Directive or if the call to eval is a direct - call (see 18.2.1.1) to the eval function that is contained in strict mode - code.

    -
    • - -
  • -

    Function code that is part of a FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, or ArrowFunction is strict function code if its GeneratorDeclaration, GeneratorExpression, MethodDefinition, or ArrowFunction is contained in strict mode code or if its FunctionBody begins - with a Directive Prologue that contains a Use Strict Directive.

    -
    • - -
  • -

    Function code that is supplied as the last argument to the built-in Function constructor is strict function code if - the last argument is a String that when processed as a FunctionBody begins with a Directive Prologue that contains a Use Strict Directive.

    -
    • -
-
- -
-

10.2.2 Non-ECMAScript Functions

- -

An ECMAScript implementation may support the evaluation of exotic function objects whose evaluative behaviour is - expressed in some implementation defined form of executable code other than via ECMAScript code. Whether a function object - is an ECMAScript code function or a non-ECMAScript function is not semantically observable from the perspective of an - ECMAScript code function that calls or is called by such a non-ECMAScript function.

-
-
-
- -
-
-

11 ECMAScript Language: Lexical Grammar

- -

The source text of an ECMAScript script is first converted into a sequence of input elements, which are tokens, line - terminators, comments, or white space. The source text is scanned from left to right, repeatedly taking the longest possible - sequence of characters as the next input element.

- -

There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar - context that is consuming the input elements. This requires multiple goal symbols for the lexical grammar. The InputElementDiv goal symbol is the default goal symbol and is used in those syntactic grammar contexts where - a leading division (/) or division-assignment (/=) operator is permitted. The InputElementRegExp goal symbol is used in all syntactic grammar contexts where a RegularExpressionLiteral is permitted. The InputElementTemplateTail goal is used in - syntactic grammar contexts where a TemplateLiteral logically continues after a substitution - element.

- -
-

NOTE There are no syntactic grammar contexts where both a leading division or - division-assignment, and a leading RegularExpressionLiteral are permitted. This is not affected by semicolon - insertion (see 11.9); in examples such as the following:

- - 
a = b
/hi/g.exec(c).map(d);
- -

where the first non-whitespace, non-comment character after a LineTerminator is slash (/) and the - syntactic context allows division or division-assignment, no semicolon is inserted at the LineTerminator. That is, - the above example is interpreted in the same way as:

- - 
a = b / hi / g.exec(c).map(d);
-
- -

Syntax

- -
-
InputElementDiv ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
DivPunctuator
-
RightBracePunctuator
-
- -
-
InputElementRegExp ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
RightBracePunctuator
-
RegularExpressionLiteral
-
- -
-
InputElementTemplateTail ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
DivPunctuator
-
TemplateSubstitutionTail
-
-
- -
-

11.1 Unicode Format-Control Characters

- -

The Unicode format-control characters (i.e., the characters in category “Cf” in the Unicode Character Database - such as left-to-right mark or right-to-left mark) are control codes used to control the formatting of a range of text in the - absence of higher-level protocols for this (such as mark-up languages).

- -

It is useful to allow format-control characters in source text to facilitate editing and display. All format control - characters may be used within comments, and within string literals, template literals, and regular expression literals.

- -

U+200C (Zero width non-joiner) and U+200D (Zero width joiner) are format-control characters that are used to make necessary distinctions when forming words or phrases - in certain languages. In ECMAScript source text, <ZWNJ> and <ZWJ> may also be used in an identifier after the first character.

- -

U+FEFF (Byte Order Mark) is a format-control character used primarily at the start of a text to mark it as Unicode and to allow - detection of the text's encoding and byte order. <BOM> characters - intended for this purpose can sometimes also appear after the start of a text, for example as a result of concatenating files. - <BOM> characters are treated as white space characters (see 0).

- -

The special treatment of certain format-control characters outside of comments, string literals, and regular expression - literals is summarized in Table 29.

- -
-
Table 29 — Format-Control Character Usage
- - - - - - - - - - - - - - - - - - - - - - - - - -
Code PointNameAbbreviationUsage
U+200CZero width non-joiner<ZWNJ>IdentifierPart
U+200DZero width joiner<ZWJ>IdentifierPart
U+FEFFByte Order Mark<BOM>Whitespace
-
-
- -
-

11.2 White - Space

- -

White space characters are used to improve source text readability and to separate tokens (indivisible lexical units) from - each other, but are otherwise insignificant. White space characters may occur between any two tokens and at the start or end - of input. White space characters may occur within a StringLiteral, a RegularExpressionLiteral, a Template, or a TemplateSubstitutionTail where they are considered significant characters forming part of a literal value. - They may also occur within a Comment, but cannot appear within any other kind of token.

- -

The ECMAScript white space characters are listed in Table 30.

- -
-
Table 30 — Whitespace Characters
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Code PointNameAbbreviation
U+0009Character Tabulation<TAB>
U+000BLINE TABULATION<VT>
U+000CForm Feed<FF>
U+0020Space<SP>
U+00A0No-break space<NBSP>
U+FEFFByte Order Mark<BOM>
Other category “Zs”Any other Unicode “Separator, Space” code point<USP>
-
- -

ECMAScript implementations must recognize as Whitespace code points listed in the “Separator - Space” (Zs) category by Unicode 5.1. ECMAScript implementations may also recognize as Whitespace - additional category Zs code points from subsequent editions of the Unicode Standard.

- -
-

NOTE Other than for the code points listed in Table 30, ECMAScript - Whitespace intentionally excludes all code points that have the Unicode “White_Space” property but which - are not classified in category “Zs”.

-
- -

Syntax

- -
-
WhiteSpace ::
-
<TAB>
-
<VT>
-
<FF>
-
<SP>
-
<NBSP>
-
<BOM>
-
<USP>
-
-
- -
-

11.3 Line - Terminators

- -

Like white space characters, line terminator characters are used to improve source text readability and to separate tokens - (indivisible lexical units) from each other. However, unlike white space characters, line terminators have some influence over - the behaviour of the syntactic grammar. In general, line terminators may occur between any two tokens, but there are a few - places where they are forbidden by the syntactic grammar. Line terminators also affect the process of automatic semicolon insertion (11.9). A line terminator cannot occur within any token except a StringLiteral, Template, or TemplateSubstitutionTail. Line - terminators may only occur within a StringLiteral token as part of a LineContinuation.

- -

A line terminator can occur within a MultiLineComment (11.4) but cannot - occur within a SingleLineComment.

- -

Line terminators are included in the set of white space characters that are matched by the \s class in regular - expressions.

- -

The ECMAScript line terminator characters are listed in Table 31.

- -
-
Table 31 — Line Terminator Characters
- - - - - - - - - - - - - - - - - - - - - - - - - - -
Code PointNameAbbreviation
U+000ALine Feed<LF>
U+000DCarriage Return<CR>
U+2028Line separator<LS>
U+2029Paragraph separator<PS>
-
- -

Only the Unicode code points in Table 31 are treated as line terminators. Other new line or line - breaking Unicode code points are not treated as line terminators but are treated as white space if they meet the requirements - listed in Table 30. The sequence <CR><LF> is commonly used as a line terminator. It should - be considered a single SourceCharacter for the purpose of reporting line numbers.

- -

Syntax

- -
-
LineTerminator ::
-
<LF>
-
<CR>
-
<LS>
-
<PS>
-
- -
-
LineTerminatorSequence ::
-
<LF>
-
<CR> [lookahead ∉ <LF> ]
-
<LS>
-
<PS>
-
<CR> <LF>
-
-
- -
-

11.4 Comments

- -

Comments can be either single or multi-line. Multi-line comments cannot nest.

- -

Because a single-line comment can contain any Unicode code point except a LineTerminator character, - and because of the general rule that a token is always as long as possible, a single-line comment always consists of all - characters from the // marker to the end of the line. However, the LineTerminator at the - end of the line is not considered to be part of the single-line comment; it is recognized separately by the lexical grammar - and becomes part of the stream of input elements for the syntactic grammar. This point is very important, because it implies - that the presence or absence of single-line comments does not affect the process of automatic semicolon insertion (see - 11.9).

- -

Comments behave like white space and are discarded except that, if a MultiLineComment contains a - line terminator character, then the entire comment is considered to be a LineTerminator for purposes - of parsing by the syntactic grammar.

- -

Syntax

- -
-
Comment ::
-
MultiLineComment
-
SingleLineComment
-
- -
-
MultiLineComment ::
-
/* MultiLineCommentCharsopt */
-
- -
-
MultiLineCommentChars ::
-
MultiLineNotAsteriskChar MultiLineCommentCharsopt
-
* PostAsteriskCommentCharsopt
-
- -
-
PostAsteriskCommentChars ::
-
MultiLineNotForwardSlashOrAsteriskChar MultiLineCommentCharsopt
-
* PostAsteriskCommentCharsopt
-
- -
-
MultiLineNotAsteriskChar ::
-
SourceCharacter but not *
-
- -
-
MultiLineNotForwardSlashOrAsteriskChar ::
-
SourceCharacter but not one of / or *
-
- -
-
SingleLineComment ::
-
// SingleLineCommentCharsopt
-
- -
-
SingleLineCommentChars ::
-
SingleLineCommentChar SingleLineCommentCharsopt
-
- -
-
SingleLineCommentChar ::
-
SourceCharacter but not LineTerminator
-
-
- -
-

11.5 Tokens

-

Syntax

- -
-
Token ::
-
IdentifierName
-
Punctuator
-
NumericLiteral
-
StringLiteral
-
Template
-
- -
-

NOTE The DivPunctuator, RegularExpressionLiteral, RightBracePunctuator, and - TemplateSubstitutionTail productions define tokens, but are not included in the Token production.

-
-
- -
-
-

11.6 Names - and Keywords

- -

IdentifierName and ReservedWord are tokens that are interpreted according - to the Default Identifier Syntax given in Unicode Standard Annex #31, Identifier and Pattern Syntax, with some small - modifications. ReservedWord is an enumerated subset of IdentifierName. The syntactic grammer defines Identifier as an IdentifierName that is not a ReservedWord (see - 11.6.2). The Unicode identifier grammar is based on character properties specified by the Unicode Standard. The Unicode - code points in the specified categories in version 5.1.0 of the Unicode standard must be treated as in those categories by - all conforming ECMAScript implementations. ECMAScript implementations may recognise identifier characters defined in later - editions of the Unicode Standard.

- -
-

NOTE 1 This standard specifies specific character additions: The dollar sign - (U+0024) and the underscore (U+005f) are permitted anywhere in an IdentifierName, and the characters zero width non-joiner (U+200C) and zero width joiner (U+200D) are - permitted anywhere after the first character of an IdentifierName.

-
- -

Unicode escape sequences are permitted in an IdentifierName, where they contribute a single - Unicode code point to the IdentifierName. The code point is expressed by the HexDigits of the UnicodeEscapeSequence (see 11.8.4). The \ preceding the UnicodeEscapeSequence and the u and { } characters, if they appear, do not - contribute code points to the IdentifierName. A UnicodeEscapeSequence cannot - be used to put a code point into an IdentifierName that would otherwise be illegal. In other words, - if a \ UnicodeEscapeSequence sequence were replaced by the SourceCharacter it contributes, the result must still be a valid IdentifierName - that has the exact same sequence of SourceCharacter elements as the original IdentifierName. All interpretations of IdentifierName within this specification - are based upon their actual code points regardless of whether or not an escape sequence was used to contribute any - particular characters.

- -

Two IdentifierName that are canonically equivalent according to the Unicode standard are - not equal unless they are represented by the exact same sequence of code points (in other words, conforming - ECMAScript implementations are only required to do bitwise comparison on IdentifierName values).

- -

Syntax

- -
-
IdentifierName ::
-
IdentifierStart
-
IdentifierName IdentifierPart
-
- -
-
IdentifierStart ::
-
UnicodeIDStart
-
$
-
_
-
\ UnicodeEscapeSequence
-
- -
-
IdentifierPart ::
-
UnicodeIDContinue
-
$
-
_
-
\ UnicodeEscapeSequence
-
<ZWNJ>
-
<ZWJ>
-
- -
-
UnicodeIDStart ::
-
any Unicode code point with the Unicode property “ID_Start”
-
- -
-
UnicodeIDContinue ::
-
any Unicode code point with the Unicode property “ID_Continue”
-
- -

The definitions of the nonterminal UnicodeEscapeSequence is given in 11.8.4.

-
- -
-
-

11.6.1 - Identifier Names

-
- -
-

11.6.1.1 Static Semantics: Early Errors

-
IdentifierStart :: \ UnicodeEscapeSequence
-
    -
  • -

    It is a Syntax Error if SV(UnicodeEscapeSequence) is - neither the UTF-16Encoding (10.1.1) of a single Unicode code point with the Unicode property - “ID_Start” nor "$″ or "_″.

    -
    • -
-
IdentifierPart :: \ UnicodeEscapeSequence
-
    -
  • -

    It is a Syntax Error if SV(UnicodeEscapeSequence) is - neither the UTF-16Encoding (10.1.1) of a single Unicode code point with the Unicode property - “ID_Continue” nor "$″ or "_″ nor the UTF-16Encoding of either <ZWNJ> or <ZAJ>.

    -
    • -
-
- -
-

11.6.1.2 Static Semantics: - StringValue

- -

See also: 11.8.4.2, 12.1.3.

- -
-
IdentifierName ::
-
IdentifierStart
-
IdentifierName IdentifierPart
-
- -
    -
  1. Return the String value consisting of the sequence of code units corresponding to IdentifierName. In - determining the sequence any occurrences of \ UnicodeEscapeSequence are first replaced with the - code point represented by the UnicodeEscapeSequence and then the code points of the entire - IdentifierName are converted to code units by UTF-16Encoding (10.1.1) each code point.
    2. -
-
-
- -
-
-

11.6.2 - Reserved Words

- -

A reserved word is an IdentifierName that cannot be used as an Identifier.

- -

Syntax

- -
-
ReservedWord ::
-
Keyword
-
FutureReservedWord
-
NullLiteral
-
BooleanLiteral
-
- -
-

NOTE The ReservedWord definitions are specified as literal sequences of specific - SourceCharacter elements. A code point in a ReservedWord cannot be expressed by a \ - UnicodeEscapeSequence.

-
-
- -
-

11.6.2.1 - Keywords

- -

The following tokens are ECMAScript keywords and may not be used as Identifiers in ECMAScript - programs.

- -

Syntax

-
Keyword :: one of
- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
breakdointypeof
caseelseinstanceofvar
catchexportnewvoid
classextendsreturnwhile
constfinallysuperwith
continueforswitchyield
debuggerfunctionthis
defaultifthrow
deleteimporttry
-
- -
-

NOTE In some contexts yield is given the semantics of an Identifier. See - 12.1.1. In strict mode - code, let is treated as a keyword through static semantic restrictions (see 12.1.1, 12.2.4.2.1, 13.2.1.1, 13.6.4.1, and 14.5.1) rather than the lexical grammar.

-
-
- -
-

11.6.2.2 Future Reserved Words

- -

The following words are used as keywords in proposed extensions and are therefore reserved to allow for the possibility - of future adoption of those extensions.

- -

Syntax

-
FutureReservedWord ::
- -
- - - - - - - -
enum
-
- -
-

NOTE Use of the following tokens within strict mode code - (see 10.2.1) is also reserved. That usage is restricted using static semantic - restrictions (see 12.1.1) rather than the lexical - grammar:

-
- -
- - - - - - - - - - - - - -
implementspackageprotectedstatic
interfaceprivatepublic
-
-
-
-
- -
-

11.7 - Punctuators

-

Syntax

-
Punctuator :: one of
- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
{()[].
...;,<><=
>===!====!==
+-*%++--
<<>>>>>&|^
!~&&||?:
=+=-=*=%=<<=
>>=>>>=&=|=^==>
-
- -
DivPunctuator :: one of
- -
- - - - - - - - - -
//=
-
- -
RightBracePunctuator ::
- -
- - - - - - - - - -
}
-
-
- -
-
-

11.8 Literals

-
- -
-

11.8.1 Null - Literals

-

Syntax

- -
-
NullLiteral ::
-
null
-
-
- -
-

11.8.2 - Boolean Literals

-

Syntax

- -
-
BooleanLiteral ::
-
true
-
false
-
-
- -
-
-

11.8.3 Numeric Literals

-

Syntax

- -
-
NumericLiteral ::
-
DecimalLiteral
-
BinaryIntegerLiteral
-
OctalIntegerLiteral
-
HexIntegerLiteral
-
- -
-
DecimalLiteral ::
-
DecimalIntegerLiteral . DecimalDigitsopt ExponentPartopt
-
. DecimalDigits ExponentPartopt
-
DecimalIntegerLiteral ExponentPartopt
-
- -
-
DecimalIntegerLiteral ::
-
0
-
NonZeroDigit DecimalDigitsopt
-
- -
-
DecimalDigits ::
-
DecimalDigit
-
DecimalDigits DecimalDigit
-
- -
-
DecimalDigit :: one of
-
0 1 2 3 4 5 6 7 8 9
-
- -
-
NonZeroDigit :: one of
-
1 2 3 4 5 6 7 8 9
-
- -
-
ExponentPart ::
-
ExponentIndicator SignedInteger
-
- -
-
ExponentIndicator :: one of
-
e E
-
- -
-
SignedInteger ::
-
DecimalDigits
-
+ DecimalDigits
-
- DecimalDigits
-
- -
-
BinaryIntegerLiteral ::
-
0b BinaryDigits
-
0B BinaryDigits
-
- -
-
BinaryDigits ::
-
BinaryDigit
-
BinaryDigits BinaryDigit
-
- -
-
BinaryDigit :: one of
-
0 1
-
- -
-
OctalIntegerLiteral ::
-
0o OctalDigits
-
0O OctalDigits
-
- -
-
OctalDigits ::
-
OctalDigit
-
OctalDigits OctalDigit
-
- -
-
OctalDigit :: one of
-
0 1 2 3 4 5 6 7
-
- -
-
HexIntegerLiteral ::
-
0x HexDigits
-
0X HexDigits
-
- -
-
HexDigits ::
-
HexDigit
-
HexDigits HexDigit
-
- -
-
HexDigit :: one of
-
0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
-
- -

The SourceCharacter immediately following a NumericLiteral must not be - an IdentifierStart or DecimalDigit.

- -
-

NOTE For example:

- - 
3in
- -

is an error and not the two input elements 3 and in.

-
- -

A conforming implementation, when processing strict mode code (see 10.2.1), must not extend the syntax of NumericLiteral to - include LegacyOctalIntegerLiteral as described in B.1.1.

-
- -
-

11.8.3.1 Static Semantics: MV’s

- -

A numeric literal stands for a value of the Number type. This value is determined in two steps: first, a mathematical - value (MV) is derived from the literal; second, this mathematical value is rounded as described below.

- -
    -
  • -

    The MV of NumericLiteral :: DecimalLiteral is the MV of DecimalLiteral.

    -
    • - -
  • -

    The MV of NumericLiteral :: BinaryIntegerLiteral is the MV of BinaryIntegerLiteral.

    -
    • - -
  • -

    The MV of NumericLiteral :: OctalIntegerLiteral is the MV of OctalIntegerLiteral.

    -
    • - -
  • -

    The MV of NumericLiteral :: HexIntegerLiteral is the MV of HexIntegerLiteral.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral . is the MV of DecimalIntegerLiteral.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits is the - MV of DecimalIntegerLiteral plus (the MV of DecimalDigits × 10–n), where - n is the number of characters in DecimalDigits.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral . ExponentPart is the MV - of DecimalIntegerLiteral × 10e, where e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits ExponentPart is (the MV of DecimalIntegerLiteral plus (the MV of DecimalDigits - × 10–n)) × 10e, where n is the number of characters in - DecimalDigits and e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of DecimalLiteral :: . DecimalDigits is the MV of DecimalDigits × - 10–n, where n is the number of characters in DecimalDigits.

    -
    • - -
  • -

    The MV of DecimalLiteral :: . DecimalDigits ExponentPart is the MV of - DecimalDigits × 10e–n, where n is the number of characters in - DecimalDigits and e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral is the MV of DecimalIntegerLiteral.

    -
    • - -
  • -

    The MV of DecimalLiteral :: DecimalIntegerLiteral ExponentPart is the MV of - DecimalIntegerLiteral × 10e, where e is the MV of ExponentPart.

    -
    • - -
  • -

    The MV of DecimalIntegerLiteral :: 0 is 0.

    -
    • - -
  • -

    The MV of DecimalIntegerLiteral :: NonZeroDigit is the MV of NonZeroDigit.

    -
    • - -
  • -

    The MV of DecimalIntegerLiteral :: NonZeroDigit DecimalDigits is (the MV of NonZeroDigit × - 10n) plus the MV of DecimalDigits, where n is the number of characters in - DecimalDigits.

    -
    • - -
  • -

    The MV of DecimalDigits :: DecimalDigit is the MV of DecimalDigit.

    -
    • - -
  • -

    The MV of DecimalDigits :: DecimalDigits DecimalDigit is (the MV of DecimalDigits × - 10) plus the MV of DecimalDigit.

    -
    • - -
  • -

    The MV of ExponentPart :: ExponentIndicator SignedInteger is the MV of - SignedInteger.

    -
    • - -
  • -

    The MV of SignedInteger :: DecimalDigits is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of SignedInteger :: + DecimalDigits is the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of SignedInteger :: - DecimalDigits is the negative of the MV of DecimalDigits.

    -
    • - -
  • -

    The MV of DecimalDigit :: 0 or of HexDigit :: 0 or of OctalDigit :: - 0 or of BinaryDigit :: 0 is 0.

    -
    • - -
  • -

    The MV of DecimalDigit :: 1 or of NonZeroDigit :: - 1 or of HexDigit :: - 1 or of OctalDigit :: 1 or
    of BinaryDigit - :: 1 is 1.

    -
    • - -
  • -

    The MV of DecimalDigit :: 2 or of NonZeroDigit :: - 2 or of HexDigit :: - 2 or of OctalDigit :: 2 is 2.

    -
    • - -
  • -

    The MV of DecimalDigit :: 3 or of NonZeroDigit :: - 3 or of HexDigit :: - 3 or of OctalDigit :: 3 is 3.

    -
    • - -
  • -

    The MV of DecimalDigit :: 4 or of NonZeroDigit :: - 4 or of HexDigit :: - 4 or of OctalDigit :: 4 is 4.

    -
    • - -
  • -

    The MV of DecimalDigit :: 5 or of NonZeroDigit :: - 5 or of HexDigit :: - 5 or of OctalDigit :: 5 is 5.

    -
    • - -
  • -

    The MV of DecimalDigit :: 6 or of NonZeroDigit :: - 6 or of HexDigit :: - 6 or of OctalDigit :: 6 is 6.

    -
    • - -
  • -

    The MV of DecimalDigit :: 7 or of NonZeroDigit :: - 7 or of HexDigit :: - 7 or of OctalDigit :: 7 is 7.

    -
    • - -
  • -

    The MV of DecimalDigit :: 8 or of NonZeroDigit :: - 8 or of HexDigit :: - 8 is 8.

    -
    • - -
  • -

    The MV of DecimalDigit :: 9 or of NonZeroDigit :: - 9 or of HexDigit :: - 9 is 9.

    -
    • - -
  • -

    The MV of HexDigit :: a or of HexDigit :: A is 10.

    -
    • - -
  • -

    The MV of HexDigit :: b or of HexDigit :: B is 11.

    -
    • - -
  • -

    The MV of HexDigit :: c or of HexDigit :: C is 12.

    -
    • - -
  • -

    The MV of HexDigit :: d or of HexDigit :: D is 13.

    -
    • - -
  • -

    The MV of HexDigit :: e or of HexDigit :: E is 14.

    -
    • - -
  • -

    The MV of HexDigit :: f or of HexDigit :: F is 15.

    -
    • - -
  • -

    The MV of BinaryIntegerLiteral :: 0b BinaryDigits is the MV of BinaryDigits.

    -
    • - -
  • -

    The MV of BinaryIntegerLiteral :: 0B BinaryDigits is the MV of BinaryDigits.

    -
    • - -
  • -

    The MV of BinaryDigits :: BinaryDigit is the MV of BinaryDigit.

    -
    • - -
  • -

    The MV of BinaryDigits :: BinaryDigits BinaryDigit is (the MV of BinaryDigits × 2) - plus the MV of BinaryDigit.

    -
    • - -
  • -

    The MV of OctalIntegerLiteral :: 0o OctalDigits is the MV of OctalDigits.

    -
    • - -
  • -

    The MV of OctalIntegerLiteral :: 0O OctalDigits is the MV of OctalDigits.

    -
    • - -
  • -

    The MV of OctalDigits :: OctalDigit is the MV of OctalDigit.

    -
    • - -
  • -

    The MV of OctalDigits :: OctalDigits OctalDigit is (the MV of OctalDigits × 8) - plus the MV of OctalDigit.

    -
    • - -
  • -

    The MV of HexIntegerLiteral :: 0x HexDigits is the MV of HexDigits.

    -
    • - -
  • -

    The MV of HexIntegerLiteral :: 0X HexDigits is the MV of HexDigits.

    -
    • - -
  • -

    The MV of HexDigits :: HexDigit is the MV of HexDigit.

    -
    • - -
  • -

    The MV of HexDigits :: HexDigits HexDigit is (the MV of HexDigits × 16) plus - the MV of HexDigit.

    -
    • -
- -

Once the exact MV for a numeric literal has been determined, it is then rounded to a value of the Number type. If the - MV is 0, then the rounded value is +0; otherwise, the rounded value must be the Number value - for the MV (as specified in 6.1.6), unless the literal is a DecimalLiteral and the literal has more than 20 significant digits, in which case the Number value may - be either the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a - 0 digit or the Number value for the MV of a literal produced by replacing each significant digit after the - 20th with a 0 digit and then incrementing the literal at the 20th significant digit position. A digit is - significant if it is not part of an ExponentPart and

- -
    -
  • it is not 0; or
    • -
  • there is a nonzero digit to its left and there is a nonzero digit, not in the ExponentPart, to its - right.
    • -
-
-
- -
-
-

11.8.4 String Literals

- -
-

NOTE A string literal is zero or more Unicode code points enclosed in single or double - quotes. Unicode code points may also be represented by an escape sequence. All characters may appear literally in a - string literal except for the closing quote character, backslash, carriage return, line separator, paragraph separator, - and line feed. Any character may appear in the form of an escape sequence. String literals evaluate to ECAMScript String - values. When generating these string values Unicode code points are UTF-16 encoded as defined in 10.1.1. Code points belonging to Basic Multilingual Plane are encoded as - a single code unit element of the string. All other code points are encoded as two code unit elements of the - string.

-
- -

Syntax

- -
-
StringLiteral ::
-
" DoubleStringCharactersopt "
-
' SingleStringCharactersopt '
-
- -
-
DoubleStringCharacters ::
-
DoubleStringCharacter DoubleStringCharactersopt
-
- -
-
SingleStringCharacters ::
-
SingleStringCharacter SingleStringCharactersopt
-
- -
-
DoubleStringCharacter ::
-
SourceCharacter but not one of " or \ or LineTerminator
-
\ EscapeSequence
-
LineContinuation
-
- -
-
SingleStringCharacter ::
-
SourceCharacter but not one of ' or \ or LineTerminator
-
\ EscapeSequence
-
LineContinuation
-
- -
-
LineContinuation ::
-
\ LineTerminatorSequence
-
- -
-
EscapeSequence ::
-
CharacterEscapeSequence
-
0 [lookahead ∉ DecimalDigit]
-
HexEscapeSequence
-
UnicodeEscapeSequence
-
- -

A conforming implementation, when processing strict mode code (see 10.2.1), must not extend the syntax of EscapeSequence to - include LegacyOctalEscapeSequence as described in B.1.1.

- -
-
CharacterEscapeSequence ::
-
SingleEscapeCharacter
-
NonEscapeCharacter
-
- -
-
SingleEscapeCharacter :: one of
-
' " \ b f n r t v
-
- -
-
NonEscapeCharacter ::
-
SourceCharacter but not one of EscapeCharacter or LineTerminator
-
- -
-
EscapeCharacter ::
-
SingleEscapeCharacter
-
DecimalDigit
-
x
-
u
-
- -
-
HexEscapeSequence ::
-
x HexDigit HexDigit
-
- -
-
UnicodeEscapeSequence ::
-
u Hex4Digits
-
u{ HexDigits }
-
- -
-
Hex4Digits ::
-
HexDigit HexDigit HexDigit HexDigit
-
- -

The definition of the nonterminal HexDigit is given in 11.8.3. SourceCharacter is defined in 10.1.

- -
-

NOTE A line terminator character cannot appear in a string literal, except as part of a - LineContinuation to produce the empty character sequence. The correct way to cause a line terminator character to - be part of the String value of a string literal is to use an escape sequence such as \n or - \u000A.

-
-
- -
-

11.8.4.1 Static Semantics: Early Errors

-
UnicodeEscapeSequence :: u{ HexDigits }
-
    -
  • It is a Syntax Error if the MV of HexDigits > 1114111.
    • -
-
- -
-

11.8.4.2 Static Semantics: - StringValue

- -

See also: 11.6.1.2, 12.1.3.

- -
-
StringLiteral ::
-
" DoubleStringCharactersopt "
-
' SingleStringCharactersopt '
-
- -
    -
  1. Return the String value whose elements are the SV of this StringLiteral.
    2. -
-
- -
-

11.8.4.3 Static Semantics: SV’s and CV’s

- -

A string literal stands for a value of the String type. The String value (SV) of the literal is described in terms of - code unit values (CV) contributed by the various parts of the string literal. As part of this process, some Unicode code - points within the string literal are interpreted as having a mathematical value (MV), as described below or in 11.8.3.

- -
    -
  • -

    The SV of StringLiteral :: "" is the empty code unit sequence.

    -
    • - -
  • -

    The SV of StringLiteral :: '' is the empty code unit sequence.

    -
    • - -
  • -

    The SV of StringLiteral :: " DoubleStringCharacters " is the SV of - DoubleStringCharacters.

    -
    • - -
  • -

    The SV of StringLiteral :: ' SingleStringCharacters ' is the SV of - SingleStringCharacters.

    -
    • - -
  • -

    The SV of DoubleStringCharacters :: DoubleStringCharacter is a sequence of one or two code units that is the CV of - DoubleStringCharacter.

    -
    • - -
  • -

    The SV of DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters is a sequence of one or - two code units that is the CV of DoubleStringCharacter followed by all the code units in the SV of - DoubleStringCharacters in order.

    -
    • - -
  • -

    The SV of SingleStringCharacters :: SingleStringCharacter is a sequence of one or two code units that is the CV of - SingleStringCharacter.

    -
    • - -
  • -

    The SV of SingleStringCharacters :: SingleStringCharacter SingleStringCharacters is a sequence of one or - two code units that is the CV of SingleStringCharacter followed by all the code units in the SV of - SingleStringCharacters in order.

    -
    • - -
  • -

    The CV of DoubleStringCharacter :: SourceCharacter but not one of " or \ or LineTerminator is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter.

    -
    • - -
  • -

    The CV of DoubleStringCharacter :: \ EscapeSequence is the CV of the EscapeSequence.

    -
    • - -
  • -

    The CV of DoubleStringCharacter :: LineContinuation is the empty character sequence.

    -
    • - -
  • -

    The CV of SingleStringCharacter :: SourceCharacter but not one of ' or \ or LineTerminator is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter .

    -
    • - -
  • -

    The CV of SingleStringCharacter :: \ EscapeSequence is the CV of the EscapeSequence.

    -
    • - -
  • -

    The CV of SingleStringCharacter :: LineContinuation is the empty character sequence.

    -
    • - -
  • -

    The CV of EscapeSequence :: CharacterEscapeSequence is the CV of the CharacterEscapeSequence.

    -
    • - -
  • -

    The CV of EscapeSequence :: 0 is the code unit value 0.

    -
    • - -
  • -

    The CV of EscapeSequence :: HexEscapeSequence is the CV of the HexEscapeSequence.

    -
    • - -
  • -

    The CV of EscapeSequence :: UnicodeEscapeSequence is the CV of the UnicodeEscapeSequence.

    -
    • - -
  • -

    The CV of CharacterEscapeSequence :: SingleEscapeCharacter is the character whose code unit value is determined by the - SingleEscapeCharacter according to Table 32.

    -
    • -
- -
-
Table 32 — String Single Character Escape Sequences
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Escape SequenceCode Unit ValueNameSymbol
\b0x0008backspace<BS>
\t0x0009horizontal tab<HT>
\n0x000Aline feed (new line)<LF>
\v0x000Bvertical tab<VT>
\f0x000Cform feed<FF>
\r0x000Dcarriage return<CR>
\"0x0022double quote"
\'0x0027single quote'
\\0x005Cbackslash\
-
- -
    -
  • -

    The CV of CharacterEscapeSequence :: NonEscapeCharacter is the CV of the NonEscapeCharacter.

    -
    • - -
  • -

    The CV of NonEscapeCharacter :: SourceCharacter but not one of EscapeCharacter - or LineTerminator is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter .

    -
    • - -
  • -

    The CV of HexEscapeSequence :: x HexDigit HexDigit is the code unit value - that is (16 times the MV of the first HexDigit) plus the MV of the second HexDigit.

    -
    • - -
  • -

    The CV of UnicodeEscapeSequence :: u Hex4Digits is the CV of Hex4Digits

    -
    • - -
  • -

    The CV of Hex4Digits :: HexDigit HexDigit HexDigit HexDigit is the code unit value that is (4096 times the MV of the first HexDigit) plus - (256 times the MV of the second HexDigit) plus (16 times the MV of the third HexDigit) plus the MV of - the fourth HexDigit.

    -
    • - -
  • -

    The CV of UnicodeEscapeSequence :: u{ HexDigits } is the UTF-16Encoding (10.1.1) of the MV of HexDigits.

    -
    • -
-
-
- -
-
-

11.8.5 Regular Expression Literals

- -
-

NOTE A regular expression literal is an input element that is converted to a RegExp object - (see 21.1.5) each time the literal is evaluated. Two regular expression - literals in a program evaluate to regular expression objects that never compare as === to each other even - if the two literals' contents are identical. A RegExp object may also be created at runtime by new RegExp - (see 21.2.3.2) or calling the RegExp constructor as a function - (21.2.3.1).

-
- -

The productions below describe the syntax for a regular expression literal and are used by the input element scanner to - find the end of the regular expression literal. The source code comprising the RegularExpressionBody and the RegularExpressionFlags are subsequently parsed - using the more stringent ECMAScript Regular Expression grammar (21.2.1).

- -

An implementation may extend the ECMAScript Regular Expression grammar defined in 21.2.1, - but it must not extend the RegularExpressionBody and RegularExpressionFlags productions defined below or the productions used by these productions.

- -

Syntax

- -
-
RegularExpressionLiteral ::
-
/ RegularExpressionBody / RegularExpressionFlags
-
- -
-
RegularExpressionBody ::
-
RegularExpressionFirstChar RegularExpressionChars
-
- -
-
RegularExpressionChars ::
-
[empty]
-
RegularExpressionChars RegularExpressionChar
-
- -
-
RegularExpressionFirstChar ::
-
RegularExpressionNonTerminator but not one of * or \ or / or [
-
RegularExpressionBackslashSequence
-
RegularExpressionClass
-
- -
-
RegularExpressionChar ::
-
RegularExpressionNonTerminator but not one of \ or / or [
-
RegularExpressionBackslashSequence
-
RegularExpressionClass
-
- -
-
RegularExpressionBackslashSequence ::
-
\ RegularExpressionNonTerminator
-
- -
-
RegularExpressionNonTerminator ::
-
SourceCharacter but not LineTerminator
-
- -
-
RegularExpressionClass ::
-
[ RegularExpressionClassChars ]
-
- -
-
RegularExpressionClassChars ::
-
[empty]
-
RegularExpressionClassChars RegularExpressionClassChar
-
- -
-
RegularExpressionClassChar ::
-
RegularExpressionNonTerminator but not one of ] or \
-
RegularExpressionBackslashSequence
-
- -
-
RegularExpressionFlags ::
-
[empty]
-
RegularExpressionFlags IdentifierPart
-
- -
-

NOTE Regular expression literals may not be empty; instead of representing an empty regular - expression literal, the characters // start a single-line comment. To specify an empty regular expression, - use: /(?:)/.

-
-
- -
-

11.8.5.1 Static Semantics: Early Errors

-
RegularExpressionFlags :: RegularExpressionFlags IdentifierPart
-
    -
  • It is a Syntax Error if IdentifierPart contains a Unicode escape sequence.
    • -
-
- -
-

11.8.5.2 Static Semantics: BodyText

-
RegularExpressionLiteral :: / RegularExpressionBody / RegularExpressionFlags
-
    -
  1. Return the source code that was recognized as RegularExpressionBody.
    2. -
-
- -
-

11.8.5.3 Static Semantics: FlagText

-
RegularExpressionLiteral :: / RegularExpressionBody / RegularExpressionFlags
-
    -
  1. Return the source code that was recognized as RegularExpressionFlags.
    2. -
-
-
- -
-
-

11.8.6 Template Literal Lexical Components

-

Syntax

- -
-
Template ::
-
NoSubstitutionTemplate
-
TemplateHead
-
- -
-
NoSubstitutionTemplate ::
-
` TemplateCharactersopt `
-
- -
-
TemplateHead ::
-
` TemplateCharactersopt ${
-
- -
-
TemplateSubstitutionTail ::
-
TemplateMiddle
-
TemplateTail
-
- -
-
TemplateMiddle ::
-
} TemplateCharactersopt ${
-
- -
-
TemplateTail ::
-
} TemplateCharactersopt `
-
- -
-
TemplateCharacters ::
-
TemplateCharacter TemplateCharactersopt
-
- -
-
TemplateCharacter ::
-
SourceCharacter but not one of ` or \ or $ or LineTerminatorSequence
-
$ [lookahead ≠ { ]
-
\ EscapeSequence
-
LineContinuation
-
LineTerminatorSequence
-
- -

A conforming implementation must not use the extended definition of EscapeSequence described in - B.1.2 when parsing a TemplateCharacter.

- -
-

NOTE TemplateSubstitutionTail is used by the InputElementTemplateTail - alternative lexical goal.

-
-
- -
-

11.8.6.1 Static Semantics: TV’s and TRV’s

- -

A template literal component is interpreted as a sequence of Unicode code points. The Template Value (TV) of a literal - component is described in terms of code unit values (CV, 11.8.4) contributed - by the various parts of the template literal component. As part of this process, some Unicode code points within the - template component are interpreted as having a mathematical value (MV, 11.8.3). In determining a TV, escape sequences are replaced by the UTF-16 code - unit(s) of the Unicode code point represented by the escape sequence. The Template Raw Value (TRV) is similar to a - Template Value with the difference that in TRVs escape sequences are interpreted literally.

- -
    -
  • -

    The TV and TRV of NoSubstitutionTemplate :: - `` is the empty code unit sequence.

    -
    • - -
  • -

    The TV and TRV of TemplateHead :: `${ is the empty code unit sequence.

    -
    • - -
  • -

    The TV and TRV of TemplateMiddle :: }${ is the empty code unit sequence.

    -
    • - -
  • -

    The TV and TRV of TemplateTail :: }` is the empty code unit sequence.

    -
    • - -
  • -

    The TV of NoSubstitutionTemplate :: ` TemplateCharacters ` is the TV of - TemplateCharacters.

    -
    • - -
  • -

    The TV of TemplateHead :: ` TemplateCharacters ${ is the TV of - TemplateCharacters.

    -
    • - -
  • -

    The TV of TemplateMiddle :: } TemplateCharacters ${ is the TV of - TemplateCharacters.

    -
    • - -
  • -

    The TV of TemplateTail :: } TemplateCharacters ` is the TV of - TemplateCharacters.

    -
    • - -
  • -

    The TV of TemplateCharacters :: TemplateCharacter is the TV of TemplateCharacter.

    -
    • - -
  • -

    The TV of TemplateCharacters :: TemplateCharacter TemplateCharacters is a sequence consisting of the - code units in the TV of TemplateCharacter followed by all the code units in the TV of TemplateCharacters - in order.

    -
    • - -
  • -

    The TV of TemplateCharacter :: SourceCharacter but not one of ` or \ or $ or LineTerminatorSequence is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter.

    -
    • - -
  • -

    The TV of TemplateCharacter :: $ is the code unit value 0x0024.

    -
    • - -
  • -

    The TV of TemplateCharacter :: \ EscapeSequence is the CV of EscapeSequence.

    -
    • - -
  • -

    The TV of TemplateCharacter :: LineContinuation is the TV of LineContinuation.

    -
    • - -
  • -

    The TV of TemplateCharacter :: LineTerminatorSequence is the TRV of LineTerminatorSequence.

    -
    • - -
  • -

    The TV of LineContinuation :: \ LineTerminatorSequence is the empty code unit sequence.

    -
    • - -
  • -

    The TRV of NoSubstitutionTemplate :: ` TemplateCharacters ` is the TRV of - TemplateCharacters.

    -
    • - -
  • -

    The TRV of TemplateHead :: ` TemplateCharacters ${ is the TRV of - TemplateCharacters.

    -
    • - -
  • -

    The TRV of TemplateMiddle :: } TemplateCharacters ${ is the TRV of - TemplateCharacters.

    -
    • - -
  • -

    The TRV of TemplateTail :: } TemplateCharacters ` is the TRV of - TemplateCharacters.

    -
    • - -
  • -

    The TRV of TemplateCharacters :: TemplateCharacter is the TRV of TemplateCharacter.

    -
    • - -
  • -

    The TRV of TemplateCharacters :: TemplateCharacter TemplateCharacters is a sequence consisting of the - code units in the TRV of TemplateCharacter followed by all the code units in the TRV of - TemplateCharacters, in order.

    -
    • - -
  • -

    The TRV of TemplateCharacter :: SourceCharacter but not one of ` or \ or $ or LineTerminatorSequence is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter.

    -
    • - -
  • -

    The TRV of TemplateCharacter :: $ is the code unit value 0x0024.

    -
    • - -
  • -

    The TRV of TemplateCharacter :: \ EscapeSequence is the sequence consisting of the code unit value - 0x005C followed by the code units of TRV of EscapeSequence.

    -
    • - -
  • -

    The TRV of TemplateCharacter :: LineContinuation is the TRV of LineContinuation.

    -
    • - -
  • -

    The TRV of TemplateCharacter :: LineTerminatorSequence is the TRV of LineTerminatorSequence.

    -
    • - -
  • -

    The TRV of EscapeSequence :: CharacterEscapeSequence is the TRV of the CharacterEscapeSequence.

    -
    • - -
  • -

    The TRV of EscapeSequence :: 0 is the code unit value 0x0030.

    -
    • - -
  • -

    The TRV of EscapeSequence :: HexEscapeSequence is the TRV of the HexEscapeSequence.

    -
    • - -
  • -

    The TRV of EscapeSequence :: UnicodeEscapeSequence is the TRV of the UnicodeEscapeSequence.

    -
    • - -
  • -

    The TRV of CharacterEscapeSequence :: SingleEscapeCharacter is the TRV of the SingleEscapeCharacter.

    -
    • - -
  • -

    The TRV of CharacterEscapeSequence :: NonEscapeCharacter is the CV of the NonEscapeCharacter.

    -
    • - -
  • -

    The TRV of SingleEscapeCharacter :: one of ' " \ b f n r t - v is the CV of the SourceCharacter that is that single character.

    -
    • - -
  • -

    The TRV of HexEscapeSequence :: x HexDigit HexDigit is the sequence - consisting of code unit value 0x0078 followed by TRV of the first HexDigit followed by the TRV of the second - HexDigit.

    -
    • - -
  • -

    The TRV of UnicodeEscapeSequence :: u Hex4Digits is the sequence consisting of code unit value 0x0075 - followed by TRV of Hex4Digits.

    -
    • - -
  • -

    The TRV of UnicodeEscapeSequence :: u{ HexDigits } is the sequence consisting of - code unit value 0x0075 followed by code unit value 0x007B followed by TRV of HexDigits followed by code unit - value 0x007D.

    -
    • - -
  • -

    The TRV of Hex4Digits :: HexDigit HexDigit HexDigit HexDigit is the sequence consisting of the TRV of the first HexDigit followed by the - TRV of the second HexDigit followed by the TRV of the third HexDigit followed by the TRV of the fourth - HexDigits.

    -
    • - -
  • -

    The TRV of HexDigits :: HexDigit is the TRV of HexDigit.

    -
    • - -
  • -

    The TRV of HexDigits :: HexDigits HexDigit is the sequence consisting of TRV of - HexDigits followed by TRV of HexDigit.

    -
    • - -
  • -

    The TRV of a HexDigit is the CV of the SourceCharacter that is that HexDigit.

    -
    • - -
  • -

    The TRV of LineContinuation :: \ LineTerminatorSequence is the sequence consisting of the code unit - value 0x005C followed by the code units of TRV of LineTerminatorSequence.

    -
    • - -
  • -

    The TRV of LineTerminatorSequence :: - <LF> is the code unit value 0x000A.

    -
    • - -
  • -

    The TRV of LineTerminatorSequence :: - <CR> is the code unit value 0x000A.

    -
    • - -
  • -

    The TRV of LineTerminatorSequence :: - <LS> is the code unit value 0x2028.

    -
    • - -
  • -

    The TRV of LineTerminatorSequence :: - <PS> is the code unit value 0x2029.

    -
    • - -
  • -

    The TRV of LineTerminatorSequence :: - <CR><LF> is the sequence consisting of the code unit value 0x000A.

    -
    • -
- -
-

NOTE TV excludes the code units of LineContinuation while TRV includes them. - <CR><LF> and <CR> LineTerminatorSequences are normalized to <LF> for both TV and TRV. An - explicit EscapeSequence is needed to include a <CR> or <CR><LF> sequence.

-
-
-
-
- -
-
-

11.9 Automatic Semicolon Insertion

- -

Certain ECMAScript statements (empty statement, let, const, import, - export, and module declarations, variable statement, expression statement, debugger - statement, continue statement, break statement, return statement, and - throw statement) must be terminated with semicolons. Such semicolons may always appear explicitly in the source - text. For convenience, however, such semicolons may be omitted from the source text in certain situations. These situations - are described by saying that semicolons are automatically inserted into the source code token stream in those - situations.

-
- -
-

11.9.1 Rules of Automatic Semicolon Insertion

- -

There are three basic rules of semicolon insertion:

- -
    -
  1. When, as the script is parsed from left to right, a token (called the offending token) is encountered that is - not allowed by any production of the grammar, then a semicolon is automatically inserted before the offending token if - one or more of the following conditions is true: -
      -
    • The offending token is separated from the previous token by at least one LineTerminator.
      • -
    • The offending token is }.
      • -
    -
    2. -
  2. When, as the script is parsed from left to right, the end of the input stream of tokens is encountered and the parser - is unable to parse the input token stream as a single complete ECMAScript script, then a semicolon is - automatically inserted at the end of the input stream.
    3. -
  3. When, as the script is parsed from left to right, a token is encountered that is allowed by some production of the - grammar, but the production is a restricted production and the token would be the first token for a terminal or - nonterminal immediately following the annotation “[no LineTerminator here]” within the restricted production (and therefore such a token is called a restricted token), and - the restricted token is separated from the previous token by at least one LineTerminator, then - a semicolon is automatically inserted before the restricted token.
    4. -
- -

However, there is an additional overriding condition on the preceding rules: a semicolon is never inserted automatically - if the semicolon would then be parsed as an empty statement or if that semicolon would become one of the two semicolons in - the header of a for statement (see 13.6.3).

- -
-

NOTE The following are the only restricted productions in the grammar:

-
- -
-
PostfixExpression[Yield] :
-
LeftHandSideExpression[?Yield] [no LineTerminator here] ++
-
LeftHandSideExpression[?Yield] [no LineTerminator here] --
-
- -
-
ContinueStatement[Yield] :
-
continue;
-
continue [no LineTerminator here] LabelIdentifier[?Yield] ;
-
- -
-
BreakStatement[Yield] :
-
break ;
-
break [no LineTerminator here] LabelIdentifier[?Yield] ;
-
- -
-
ReturnStatement[Yield] :
-
return [no LineTerminator here] Expression ;
-
return [no LineTerminator here] Expression[In, ?Yield] ;
-
- -
-
ThrowStatement[Yield] :
-
throw [no LineTerminator here] Expression[In, ?Yield] ;
-
- -
-
ArrowFunction[In, Yield] :
-
ArrowParameters[?Yield] [no LineTerminator here] => ConciseBody[?In]
-
- -
-
YieldExpression[In] :
-
yield [no LineTerminator here] * [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]
-
yield [no LineTerminator here] [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]
-
- -
-
ModuleImport :
-
module [no LineTerminator here] ImportedBinding FromClause ;
-
- -

The practical effect of these restricted productions is as follows:

- -

When a ++ or -- token is encountered where the parser would treat it as a postfix operator, and - at least one LineTerminator occurred between the preceding token and the ++ or - -- token, then a semicolon is automatically inserted before the ++ or -- token.

- -

When a continue, break, return, throw, or yield token is - encountered and a LineTerminator is encountered before the next token, a semicolon is automatically - inserted after the continue, break, return, throw, or yield - token.

- -

The resulting practical advice to ECMAScript programmers is:

- -

A postfix ++ or -- operator should appear on the same line as its operand.

- -

An Expression in a return or throw statement or an AssignmentExpression in a yield expression should start on the same line as the - return, throw, or yield token.

- -

An IdentifierReference in a break or continue statement should be on - the same line as the break or continue token.

-
- -
-

11.9.2 Examples of Automatic Semicolon Insertion

- -

The source

- - 
{ 1 2 } 3
- -

is not a valid sentence in the ECMAScript grammar, even with the automatic - semicolon insertion rules. In contrast, the source

- - 
{ 1
2 } 3
- -

is also not a valid ECMAScript sentence, but is transformed by automatic - semicolon insertion into the following:

- - 
{ 1
;2 ;} 3;
- -

which is a valid ECMAScript sentence.

- -

The source

- - 
for (a; b
)
- -

is not a valid ECMAScript sentence and is not altered by automatic semicolon - insertion because the semicolon is needed for the header of a for statement. Automatic semicolon insertion - never inserts one of the two semicolons in the header of a for statement.

- -

The source

- - 
return
a + b
- -

is transformed by automatic semicolon insertion into the following:

- - 
return;
a + b;
- -
-

NOTE The expression a + b is not treated as a value to be returned by the - return statement, because a LineTerminator separates it from the token return.

-
- -

The source

- - 
a = b
++c
- -

is transformed by automatic semicolon insertion into the following:

- - 
a = b;
++c;
- -
-

NOTE The token ++ is not treated as a postfix operator applying to the variable - b, because a LineTerminator occurs between b and ++.

-
- -

The source

- - 
if (a > b)
else c = d
- -

is not a valid ECMAScript sentence and is not altered by automatic semicolon - insertion before the else token, even though no production of the grammar applies at that point, because an - automatically inserted semicolon would then be parsed as an empty statement.

- -

The source

- - 
a = b + c
(d + e).print()
- -

is not transformed by automatic semicolon insertion, because the - parenthesized expression that begins the second line can be interpreted as an argument list for a function call:

- - 
a = b + c(d + e).print()
- -

In the circumstance that an assignment statement must begin with a left parenthesis, it is a good idea for the programmer - to provide an explicit semicolon at the end of the preceding statement rather than to rely on automatic semicolon insertion.

-
-
-
- -
-
-

12 - ECMAScript Language: Expressions

-
- -
-
-

12.1 - Identifiers

- -

Syntax

- -
-
IdentifierReference[Yield] :
-
Identifier
-
[~Yield] yield
-
- -

BindingIdentifier[Default, Yield] :

- -

[+Default] default
[~Yield] yield
Identifier

- -
-
LabelIdentifier[Yield] :
-
Identifier
-
[~Yield] yield
-
- -
-
Identifier :
-
IdentifierName but not ReservedWord
-
-
- -
-

12.1.1 Static Semantics: Early Errors

-
BindingIdentifier : Identifier
-
    -
  • -

    It is a Syntax Error if this production is contained in strict code and the - StringValue of Identifier is "arguments" or "eval".

    -
    • -
- -

IdentifierReference[Yield] : Identifier

- -

BindingIdentifier[Default, Yield] : - Identifier

- -

LabelIdentifier [Yield] : - Identifier

- -
    -
  • -

    It is a Syntax Error if this production has a [Yield] parameter and the StringValue of Identifier is "yield".

    -
    • -
- -

IdentifierReference : yield

- -

BindingIdentifier : yield

- -
LabelIdentifier : yield
-
    -
  • -

    It is a Syntax Error if this production is contained in strict - code.

    -
    • - -
  • -

    It is a Syntax Error if this production is within the FunctionBody of a GeneratorMethod, GeneratorDeclaration, or GeneratorExpression.

    -
    • -
-
Identifier :: IdentifierName but not ReservedWord
-
    -
  • -

    It is a Syntax Error if this production is contained in strict code and the - StringValue of IdentifierName is: "implements", "interface", - "let", "package", "private", "protected", "public", or - "static".

    -
    • - -
  • -

    It is a Syntax Error if this production is contained in strict code and the - StringValue of IdentifierName is "yield".

    -
    • - -
  • -

    It is a Syntax Error if StringValue of IdentifierName is the same string value as the - StringValue of any ReservedWord except for yield.

    -
    • -
- -
-

NOTE StringValue of IdentifierName - normalizes any Unicode escape sequences in IdentifierName hence such escapes cannot be used to write an - Identifier whose code point sequence is the same as a ReservedWord.

-
-
- -
-

12.1.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
BindingIdentifier : Identifier
-
    -
  1. Return a new List containing the StringValue of - Identifier.
    2. -
-
BindingIdentifier : yield
-
    -
  1. Return a new List containing "yield".
    2. -
-
BindingIdentifier : default
-
    -
  1. Return a new List containing "default".
    2. -
-
- -
-

12.1.3 Static Semantics: - StringValue

- -

See also: 11.6.1.2, 11.8.4.2.

- -

IdentifierReference : yield

- -

BindingIdentifier : yield

- -
LabelIdentifier : yield
-
    -
  1. Return "yield".
    2. -
-
BindingIdentifier : default
-
    -
  1. Return "default".
    2. -
-
Identifier : IdentifierName but not ReservedWord
-
    -
  1. Return the StringValue of IdentifierName.
    2. -
-
- -
-
-

12.1.4 Runtime Semantics: BindingInitialization

- -

With arguments value and environment.

- -

See also: 12.2.4.2.2, 13.2.2.2, 13.2.3.4, 13.14.3.

- -
-

NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for - var statements formal parameter lists of non-strict functions. In those cases a lexical binding is hosted - and preinitialized prior to evaluation of its initializer.

-
- -
BindingIdentifier : Identifier
-
    -
  1. Let name be StringValue of Identifier.
    2. -
  2. Return InitializeBoundName( name, value, - environment).
    3. -
-
BindingIdentifier : default
-
    -
  1. Return InitializeBoundName("default", value, - environment).
    2. -
-
BindingIdentifier : yield
-
    -
  1. Return InitializeBoundName("yield", value, - environment).
    2. -
-
- -
-

12.1.4.1 Runtime Semantics: InitializeBoundName(name, value, environment)

-
    -
  1. Assert: Type(name) is String.
    2. -
  2. If environment is not undefined, then -
      -
    1. Let env be the environment record component of environment.
      2. -
    2. Call the InitializeBinding concrete method of env passing name and value as the - arguments.
      3. -
    3. Return NormalCompletion(undefined).
      4. -
    -
    3. -
  3. Else -
      -
    1. Let lhs be ResolveBinding(name).
      2. -
    2. Return PutValue(lhs, value).
      3. -
    -
    4. -
-
-
- -
-

12.1.5 Runtime Semantics: Evaluation

-
IdentifierReference : Identifier
-
    -
  1. Return ResolveBinding(StringValue(Identifier)).
    2. -
-
IdentifierReference : yield
-
    -
  1. Return ResolveBinding(″yield″).
    2. -
- -
-

NOTE 1: The result of evaluating an IdentifierReference is always a value of type Reference.

-
- -
-

NOTE 2: In non-strict code, the keyword yield - may be used as an identifier. Evaluating the IdentifierReference production resolves the binding of - yield as if it was an Identifier. Early Error restriction ensures that such an evaluation only can - occur for non-strict code. See 13.2.1 - for the handling of yield in binding creation contexts.

-
-
-
- -
-
-

12.2 - Primary Expression

-

Syntax

- -
-
PrimaryExpression[Yield] :
-
this
-
IdentifierReference[?Yield]
-
Literal
-
ArrayInitializer[?Yield]
-
ObjectLiteral[?Yield]
-
FunctionExpression
-
ClassExpression
-
GeneratorExpression
-
GeneratorComprehension[?Yield]
-
RegularExpressionLiteral
-
TemplateLiteral[?Yield]
-
CoverParenthesizedExpressionAndArrowParameterList[?Yield]
-
- -
-
CoverParenthesizedExpressionAndArrowParameterList[Yield] :
-
( Expression[In, ?Yield] )
-
( )
-
( ... BindingIdentifier[?Yield] )
-
( Expression[In, ?Yield] , ... BindingIdentifier[?Yield] )
-
- -

Supplemental Syntax

- -

When processing the production

- -

PrimaryExpression[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]
the interpretation of CoverParenthesizedExpressionAndArrowParameterList is - refined using the following grammar:

- -
-
ParenthesizedExpression[Yield] :
-
( Expression[In, ?Yield] )
-
-
- -
-
-

12.2.0 Semantics

-
- -
-

12.2.0.1 Static Semantics: CoveredParenthesizedExpression

-
CoverParenthesizedExpressionAndArrowParameterList[Yield] : ( Expression[In, ?Yield] )
-
    -
  1. Return the result of parsing the lexical token stream matched by - CoverParenthesizedExpressionAndArrowParameterList[Yield] using either - ParenthesizedExpression or ParenthesizedExpression[Yield] as the goal symbol depending upon - whether the [Yield] grammar parameter was present when - CoverParenthesizedExpressionAndArrowParameterList was matched.
    2. -
-
- -
-

12.2.0.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
PrimaryExpression :
-
this
-
IdentifierReference
-
Literal
-
ArrayInitializer
-
ObjectLiteral
-
GeneratorComprehension
-
RegularExpressionLiteral
-
TemplateLiteral
-
- -
    -
  1. Return false.
    2. -
-
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  1. Let expr be CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
    2. -
  2. Return IsFunctionDefinition of expr.
    3. -
-
- -
-

12.2.0.3 Static Semantics: IsIdentifierRef

- -

See also: 12.3.1.3.

- -
-
PrimaryExpression :
-
IdentifierReference
-
- -
    -
  1. Return true.
    2. -
- -
-
PrimaryExpression :
-
this
-
Literal
-
ArrayInitializer
-
ObjectLiteral
-
FunctionExpression
-
ClassExpression
-
GeneratorExpression
-
GeneratorComprehension
-
RegularExpressionLiteral
-
TemplateLiteral
-
CoverParenthesizedExpressionAndArrowParameterList
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.2.0.4 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
PrimaryExpression :
-
this
-
Literal
-
ArrayInitializer
-
ObjectLiteral
-
FunctionExpression
-
ClassExpression
-
GeneratorExpression
-
GeneratorComprehension
-
RegularExpressionLiteral
-
TemplateLiteral
-
- -
    -
  1. Return false.
    2. -
-
PrimaryExpression : IdentifierReference
-
    -
  1. If this PrimaryExpression is contained in strict code and StringValue of - IdentifierReference is "eval" or "arguments", then return false.
    2. -
  2. Return true.
    3. -
-
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  1. Let expr be CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
    2. -
  2. Return IsValidSimpleAssignmentTarget of expr.
    3. -
-
-
- -
-
-

12.2.1 The - this Keyword

-
- -
-

12.2.1.1 Runtime Semantics: Evaluation

-
PrimaryExpression : this
-
    -
  1. Return ResolveThisBinding( ) .
    2. -
-
-
- -
-

12.2.2 - Identifier Reference

- -

See 12.1 for PrimaryExpression : IdentifierReference .

-
- -
-
-

12.2.3 Literals

-

Syntax

- -
-
Literal :
-
NullLiteral
-
ValueLiteral
-
- -
-
ValueLiteral :
-
BooleanLiteral
-
NumericLiteral
-
StringLiteral
-
-
- -
-

12.2.3.1 Runtime Semantics: Evaluation

-
Literal : NullLiteral
-
    -
  1. Return null.
    2. -
-
ValueLiteral : BooleanLiteral
-
    -
  1. Return false if BooleanLiteral is the token false.
    2. -
  2. Return true if BooleanLiteral is the token true.
    3. -
-
ValueLiteral : NumericLiteral
-
    -
  1. Return the number whose value is MV of NumericLiteral as defined in 11.8.3.
    2. -
-
ValueLiteral : StringLiteral
-
    -
  1. Return the StringValue of StringLiteral as defined in 11.8.4.2.
    2. -
-
-
- -
-
-

12.2.4 - Array Initializer

-

Syntax

- -
-
ArrayInitializer[Yield] :
-
ArrayLiteral[?Yield]
-
ArrayComprehension[?Yield]
-
-
- -
-
-

12.2.4.1 - Array Literal

- -
-

NOTE An ArrayLiteral is an expression describing the initialization of an Array - object, using a list, of zero or more expressions each of which represents an array element, enclosed in square - brackets. The elements need not be literals; they are evaluated each time the array initializer is evaluated.

-
- -

Array elements may be elided at the beginning, middle or end of the element list. Whenever a comma in the element - list is not preceded by an AssignmentExpression (i.e., a comma at the beginning or after another - comma), the missing array element contributes to the length of the Array and increases the index of subsequent elements. - Elided array elements are not defined. If an element is elided at the end of an array, that element does not contribute - to the length of the Array.

- -

Syntax

- -
-
ArrayLiteral[Yield] :
-
[ Elisionopt ]
-
[ ElementList[?Yield] ]
-
[ ElementList[?Yield] , Elisionopt ]
-
- -
-
ElementList[Yield] :
-
Elisionopt AssignmentExpression[In, ?Yield]
-
Elisionopt SpreadElement[?Yield]
-
ElementList[?Yield] , Elisionopt AssignmentExpression[In, ?Yield]
-
ElementList[?Yield] , Elisionopt SpreadElement[?Yield]
-
- -
-
Elision :
-
,
-
Elision ,
-
- -
-
SpreadElement[Yield] :
-
... AssignmentExpression[In, ?Yield]
-
-
- -
-

12.2.4.1.1 Static Semantics: ElisionWidth

-
Elision : ,
-
    -
  1. Return the numeric value 1.
    2. -
-
Elision : Elision ,
-
    -
  1. Let preceding be the ElisionWidth of Elision.
    2. -
  2. Return preceding+1.
    3. -
-
- -
-

12.2.4.1.2 Runtime Semantics: ArrayAccumulation

- -

With parameters array and nextIndex.

- -
ElementList : Elisionopt AssignmentExpression
-
    -
  1. Let padding be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    2. -
  2. Let initResult be the result of evaluating AssignmentExpression.
    3. -
  3. Let initValue be GetValue(initResult).
    4. -
  4. ReturnIfAbrupt(initValue).
    5. -
  5. Let created be the result of calling the [[DefineOwnProperty]] internal method of array with - arguments ToString(ToUint32(nextIndex+padding)) and - the PropertyDescriptor{ [[Value]]: initValue, [[Writable]]: true, [[Enumerable]]: true, - [[Configurable]]: true}.
    6. -
  6. Assert: created is true.
    7. -
  7. Return nextIndex+padding+1.
    8. -
-
ElementList : Elisionopt SpreadElement
-
    -
  1. Let padding be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    2. -
  2. Return the result of performing ArrayAccumulation for SpreadElement with arguments array and - nextIndex+padding.
    3. -
-
ElementList : ElementList , Elisionopt AssignmentExpression
-
    -
  1. Let postIndex be the result of performing ArrayAccumulation for ElementList with arguments - array and nextIndex.
    2. -
  2. ReturnIfAbrupt(postIndex).
    3. -
  3. Let padding be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    4. -
  4. Let initResult be the result of evaluating AssignmentExpression.
    5. -
  5. Let initValue be GetValue(initResult).
    6. -
  6. ReturnIfAbrupt(initValue).
    7. -
  7. Let created be the result of calling the [[DefineOwnProperty]] internal method of array with - arguments ToString(ToUint32(postIndex+padding)) and the PropertyDescriptor{ [[Value]]: - initValue, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true}.
    8. -
  8. Assert: created is true.
    9. -
  9. Return postIndex+padding+1.
    10. -
-
ElementList : ElementList , Elisionopt SpreadElement
-
    -
  1. Let postIndex be the result of performing ArrayAccumulation for ElementList with arguments - array and nextIndex.
    2. -
  2. ReturnIfAbrupt(postIndex).
    3. -
  3. Let padding be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    4. -
  4. Return the result of performing ArrayAccumulation for SpreadElement with arguments array and - postIndex+padding.
    5. -
-
SpreadElement : ... AssignmentExpression
-
    -
  1. Let spreadRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let spreadObj be GetValue(spreadRef).
    3. -
  3. ReturnIfAbrupt(spreadObj).
    4. -
  4. If Type(spreadObj) is not Object, then throw a - TypeError exception.
    5. -
  5. Let iterator be GetIterator(spreadObj).
    6. -
  6. ReturnIfAbrupt(iterator).
    7. -
  7. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return nextIndex.
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let defineStatus be CreateDataPropertyOrThrow(array, ToString(ToUint32(nextIndex)), - nextValue).
      7. -
    7. ReturnIfAbrupt(defineStatus).
      8. -
    8. Let nextIndex be nextIndex + 1.
      9. -
    -
    8. -
- -
-

NOTE [[DefineOwnProperty]] is used to ensure that own properties are defined for the array - even if the standard built-in Array prototype object has been modified in a manner that would preclude the creation of - new own properties using [[Set]].

-
-
- -
-

12.2.4.1.3 Runtime Semantics: Evaluation

-
ArrayLiteral : [ Elisionopt ]
-
    -
  1. Let array be ArrayCreate(0).
    2. -
  2. Let pad be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    3. -
  3. Perform Put(array, "length", pad, - false).
    4. -
  4. Return array.
    5. -
-
ArrayLiteral : [ ElementList ]
-
    -
  1. Let array be ArrayCreate(0).
    2. -
  2. Let len be the result of performing ArrayAccumulation for ElementList with arguments array - and 0.
    3. -
  3. ReturnIfAbrupt(len).
    4. -
  4. Perform Put(array, "length", len, - false).
    5. -
  5. Return array.
    6. -
-
ArrayLiteral : [ ElementList , Elisionopt ]
-
    -
  1. Let array be ArrayCreate(0).
    2. -
  2. Let len be the result of performing ArrayAccumulation for ElementList with arguments array - and 0.
    3. -
  3. ReturnIfAbrupt(len).
    4. -
  4. Let padding be the ElisionWidth of Elision; if Elision is not present, use the numeric value - zero.
    5. -
  5. Perform Put(array, "length", ToUint32(padding+len), false).
    6. -
  6. Return array.
    7. -
-
-
- -
-
-

12.2.4.2 Array Comprehension

-

Syntax

- -
-
ArrayComprehension[Yield] :
-
[ Comprehension[?Yield] ]
-
- -
-
Comprehension[Yield] :
-
ComprehensionFor[?Yield] ComprehensionTail[?Yield]
-
- -
-
ComprehensionTail[Yield] :
-
AssignmentExpression[In, ?Yield]
-
ComprehensionFor[?Yield] ComprehensionTail[?Yield]
-
ComprehensionIf[?Yield] ComprehensionTail[?Yield]
-
- -
-
ComprehensionFor[Yield] :
-
for ( ForBinding[?Yield] of AssignmentExpression[In, ?Yield] )
-
- -
-
ComprehensionIf[Yield] :
-
if ( AssignmentExpression[In, ?Yield] )
-
- -
-
ForBinding[Yield] :
-
BindingIdentifier[?Yield]
-
BindingPattern[?Yield]
-
-
- -
-

12.2.4.2.1 Static Semantics: Early Errors

-
ComprehensionFor : for ( ForBinding of AssignmentExpression )
-
    -
  • It is a Syntax Error if the BoundNames of ForBinding contains "let".
    • -
  • It is a Syntax Error if the BoundNames of ForBinding contains any duplicate entries.
    • -
-
- -
-

12.2.4.2.2 Runtime Semantics: BindingInitialization

- -

With arguments value and environment.

- -

See also: Error! Reference source not found., 13.2.2.2, 13.2.3.4, 13.14.3.

- -
-

NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for - var statements formal parameter lists of non-strict functions. In those cases a lexical binding is hosted - and preinitialized prior to evaluation of its initializer.

-
- -
ForBinding : BindingPattern
-
    -
  1. If Type(value) is not Object, then throw a - TypeError exception.
    2. -
  2. Return the result of performing BindingInitialization for BindingPattern passing value and - environment as the arguments.
    3. -
-
- -
-

12.2.4.2.3 Runtime Semantics: ComprehensionEvaluation

- -

With argument accumulator.

- -
-

NOTE undefined is passed for accumulator to indicate that a comprehension - component is being evaluated as part of a generator comprehension. Otherwise, the value of accumulator is the - array object into which the elements of an array comprehension are to be accumulated.

-
- -
Comprehension : ComprehensionFor ComprehensionTail
-
    -
  1. Return the result of performing ComprehensionComponentEvaluation for ComprehensionFor with arguments - ComprehensionTail and accumulator.
    2. -
- -

ComprehensionTail : ComprehensionFor ComprehensionTail

- -
    -
  1. Return the result of performing ComprehensionComponentEvaluation for ComprehensionFor with arguments - ComprehensionTail and accumulator.
    2. -
- -

ComprehensionTail : ComprehensionIf ComprehensionTail

- -
    -
  1. Return the result of performing ComprehensionComponentEvaluation for ComprehensionIf with arguments - ComprehensionTail and accumulator.
    2. -
- -

ComprehensionTail : AssignmentExpression

- -
    -
  1. Let valueRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let value be GetValue(valueRef).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. If accumulator is not undefined, then -
      -
    1. Assert: this is part of an array comprehension.
      2. -
    2. Assert: accumulator is an exotic array object so access to its - length property should never fail.
      3. -
    3. Let len be Get(accumulator, "length").
      4. -
    4. If len≥232-1, then throw a RangeError exception.
      5. -
    5. Let putStatus be Put(accumulator, ToString(len), value, true).
      6. -
    6. ReturnIfAbrupt(putStatus).
      7. -
    7. Increase len by 1.
      8. -
    8. Let putStatus be Put(accumulator, "length", - len, true).
      9. -
    9. ReturnIfAbrupt(putStatus).
      10. -
    10. Return NormalCompletion(undefined).
      11. -
    -
    5. -
  5. Assert: accumulator is undefined, so this is part of a - generator comprehension.
    6. -
  6. Let yieldStatus be GeneratorYield(CreateIterResultObject(value, false)).
    7. -
  7. ReturnIfAbrupt(yieldStatus).
    8. -
  8. Return NormalCompletion(undefined).
    9. -
-
- -
-

12.2.4.2.4 Runtime Semantics: ComprehensionComponentEvaluation

- -

With arguments tail and accumulator.

- -
-

NOTE undefined is passed for accumulator to indicate that a comprehension - component is being evaluated as part of a generator comprehension. Otherwise, the value of accumulator is the - array object into which the elements of an array comprehension are to be accumulated.

-
- -
ComprehensionFor : for ( ForBinding of AssignmentExpression )
-
    -
  1. Let exprRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let exprValue be GetValue(exprRef).
    3. -
  3. if exprValue is null or undefined, then return NormalCompletion(undefined).
    4. -
  4. Let obj be ToObject(exprValue).
    5. -
  5. ReturnIfAbrupt(obj).
    6. -
  6. Let keys be GetIterator(obj).
    7. -
  7. ReturnIfAbrupt(keys).
    8. -
  8. Let oldEnv be the running execution context’s LexicalEnvironment.
    9. -
  9. Repeat -
      -
    1. Let nextResult be IteratorStep(keys).
      2. -
    2. ReturnIfAbrupt(nextResult).
      3. -
    3. If nextResult is false, then return NormalCompletion(undefined).
      4. -
    4. Let nextValue be IteratorValue(nextResult);
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let forEnv be NewDeclarativeEnvironment(oldEnv).
      7. -
    7. For each element name of the BoundNames of ForBinding do -
        -
      1. Call forEnv’s CreateMutableBinding concrete method with argument name.
        2. -
      2. Assert: The above call to CreateMutableBinding will never return - an abrupt completion.
        3. -
      -
      8. -
    8. Let status be the result of performing BindingInitialization for ForBinding passing - nextValue and forEnv as the arguments.
      9. -
    9. ReturnIfAbrupt(status).
      10. -
    10. Set the running execution context’s LexicalEnvironment to forEnv.
      11. -
    11. Let continue be the result of performing ComprehensionEvaluation for tail with argument - accumulator.
      12. -
    12. Set the running execution context’s LexicalEnvironment to oldEnv.
      13. -
    13. ReturnIfAbrupt(continue).
      14. -
    -
    10. -
-
ComprehensionIf : if ( AssignmentExpression )
-
    -
  1. Let valueRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let value be GetValue(valueRef).
    3. -
  3. Let boolValue be ToBoolean(value).
    4. -
  4. ReturnIfAbrupt(boolValue).
    5. -
  5. If boolValue is true, then -
      -
    1. Return the result of performing ComprehensionEvaluation for tail with argument accumulator.
      2. -
    -
    6. -
  6. Else, -
      -
    1. Return NormalCompletion(undefined).
      2. -
    -
    7. -
-
- -
-

12.2.4.2.5 Runtime Semantics: Evaluation

-
ArrayComprehension : [ Comprehension ]
-
    -
  1. Let array be ArrayCreate(0).
    2. -
  2. Let status be the result of performing ComprehensionEvaluation for Comprehension with argument - array.
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Return array.
    5. -
-
Comprehension : ComprehensionFor ComprehensionTail
-
    -
  1. Return the result of performing ComprehensionEvaluation for this Comprehension with argument - undefined.
    2. -
- -
-

NOTE This action is only invoked for a Comprehension that is part of a - GeneratorComprehension.

-
-
-
-
- -
-
-

12.2.5 - Object Initializer

- -
-

NOTE 1 An object initializer is an expression describing the initialization of an Object, - written in a form resembling a literal. It is a list of zero or more pairs of property names and associated values, - enclosed in curly braces. The values need not be literals; they are evaluated each time the object initializer is - evaluated.

-
- -

Syntax

- -
-
ObjectLiteral[Yield] :
-
{ }
-
{ PropertyDefinitionList[?Yield] }
-
{ PropertyDefinitionList[?Yield] , }
-
- -
-
PropertyDefinitionList[Yield] :
-
PropertyDefinition[?Yield]
-
PropertyDefinitionList[?Yield] , PropertyDefinition[?Yield]
-
- -
-
PropertyDefinition[Yield] :
-
IdentifierReference[?Yield]
-
CoverInitializedName[?Yield]
-
PropertyName[?Yield] : AssignmentExpression[In, ?Yield]
-
MethodDefinition[?Yield]
-
- -
-
PropertyName[Yield,GeneratorParameter] :
-
LiteralPropertyName
-
[+GeneratorParameter] ComputedPropertyName
-
[~GeneratorParameter] ComputedPropertyName[?Yield]
-
- -
-
LiteralPropertyName :
-
IdentifierName
-
StringLiteral
-
NumericLiteral
-
- -
-
ComputedPropertyName[Yield] :
-
[ AssignmentExpression[In, ?Yield] ]
-
- -
-
CoverInitializedName[Yield] :
-
IdentifierReference[?Yield] Initializer[In, ?Yield]
-
- -
-
Initializer[In, Yield] :
-
= AssignmentExpression[?In, ?Yield]
-
- -
-

NOTE 2 MethodDefinition is defined in 14.3.

-
- -
-

NOTE 3 In certain contexts, ObjectLiteral is used as a cover grammar for a more - restricted secondary grammar. The CoverInitializedName production is necessary to fully cover these secondary - grammars. However, use of this production results in an early Syntax Error in normal contexts where an actual - ObjectLiteral is expected.

-
-
- -
-

12.2.5.1 Static Semantics: Early Errors

- -

In addition to describing an actual object initializer the ObjectLiteral productions are also - used as a cover grammar for ObjectAssignmentPattern (12.14.5). and may be recognized as part of a CoverParenthesizedExpressionAndArrowParameterList. When ObjectLiteral appears in - a context where ObjectAssignmentPattern is required the following Early Error rules are not - applied. In addition, they are not applied when initially parsing a - CoverParenthesizedExpressionAndArrowParameterList.

- -
ObjectLiteral : { PropertyDefinitionList }
- -

and

- -
ObjectLiteral : { PropertyDefinitionList , }
-
    -
  • -

    It is a Syntax Error if PropertyNameList of PropertyDefinitionList contains any duplicate entries, unless one of the following conditions are - true for each duplicate entry:

    - -
      -
    1. The source code corresponding to PropertyDefinitionList is not strict code and all occurrences in the list of the duplicated entry were - obtained from productions of the form PropertyDefinition : PropertyName : AssignmentExpression .
      2. -
    2. The duplicated entry occurs exactly twice in the list and one occurrence was obtained from a get - accessor MethodDefinition and the other occurrence was obtained from a set - accessor MethodDefinition.
      3. -
    -
    • -
-
PropertyDefinition : CoverInitializedName
-
    -
  • Always throw a Syntax Error if this production is present
    • -
- -
-

NOTE This production exists so that ObjectLiteral can serve as a cover grammar for - ObjectAssignmentPattern (12.14.5). It cannot occur in an actual - object initializer.

-
-
- -
-

12.2.5.2 Static Semantics: ComputedPropertyContains

- -

With parameter symbol.

- -

See also: 14.3.2, 14.4.3, 14.5.5.

- -
PropertyName : LiteralPropertyName
-
    -
  1. Return false.
    2. -
-
PropertyName : ComputedPropertyName
-
    -
  1. Return the result of ComputedPropertyName Contains symbol.
    2. -
-
- -
-

12.2.5.3 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.3.1.1, 14.1.4, 14.2.3, 14.4.3, 14.5.4

- -
PropertyDefinition : MethodDefinition
-
    -
  1. If symbol is MethodDefinition, return true.
    2. -
  2. Return the result of ComputedPropertyContains for MethodDefinition with argument symbol.
    3. -
- -
-

NOTE Static semantic rules that depend upon substructure generally do not look into function - definitions.

-
- -
LiteralPropertyName : IdentifierName
-
    -
  1. If symbol is a ReservedWord, return false.
    2. -
  2. If symbol is an Identifier and StringValue of symbol is the same value as the StringValue of - IdentifierName, return true;
    3. -
  3. Return false.
    4. -
-
- -
-

12.2.5.4 Static Semantics: HasComputedPropertyKey

- -

See also: 14.3.4, 14.4.5

- -
PropertyDefinitionList : PropertyDefinitionList , PropertyDefinition
-
    -
  1. If HasComputedPropertyKey of PropertyDefinitionList is true, then return true.
    2. -
  2. Return HasComputedPropertyKey of PropertyDefinition.
    3. -
-
PropertyDefinition : IdentifierReference
-
    -
  1. Return false.
    2. -
-
PropertyDefinition : PropertyName : AssignmentExpression
-
    -
  1. Return IsComputedPropertyKey of PropertyName.
    2. -
-
- -
-

12.2.5.5 Static Semantics: IsComputedPropertyKey

-
PropertyName : LiteralPropertyName
-
    -
  1. Return false.
    2. -
-
PropertyName : ComputedPropertyName
-
    -
  1. Return true.
    2. -
-
- -
-

12.2.5.6 Static Semantics: PropName

- -

See also: 14.3.5, 14.4.10, 14.5.13

- -
PropertyDefinition : IdentifierReference
-
    -
  1. Return StringValue of IdentifierReference.
    2. -
-
PropertyDefinition : PropertyName : AssignmentExpression
-
    -
  1. Return PropName of PropertyName.
    2. -
-
LiteralPropertyName : IdentifierName
-
    -
  1. Return StringValue of IdentifierName.
    2. -
-
LiteralPropertyName : StringLiteral
-
    -
  1. Return a String value whose characters are the SV of the StringLiteral.
    2. -
-
LiteralPropertyName : NumericLiteral
-
    -
  1. Let nbr be the result of forming the value of the NumericLiteral.
    2. -
  2. Return ToString(nbr).
    3. -
-
ComputedPropertyName : [ AssignmentExpression ]
-
    -
  1. Return empty.
    2. -
-
- -
-

12.2.5.7 Static Semantics: PropertyNameList

-
PropertyDefinitionList : PropertyDefinition
-
    -
  1. If PropName of PropertyDefinition is empty, return a new empty - List.
    2. -
  2. Return a new List containing PropName of - PropertyDefinition.
    3. -
-
PropertyDefinitionList : PropertyDefinitionList , PropertyDefinition
-
    -
  1. Let list be PropertyNameList of PropertyDefinitionList.
    2. -
  2. If PropName of PropertyDefinition is empty, return - list.
    3. -
  3. Append PropName of PropertyDefinition to the end of list.
    4. -
  4. Return list.
    5. -
-
- -
-

12.2.5.8 Runtime Semantics: Evaluation

-
ObjectLiteral : { }
-
    -
  1. Return ObjectCreate(%ObjectPrototype%).
    2. -
- -

ObjectLiteral :
{ PropertyDefinitionList }
 { PropertyDefinitionList , - }

- -
    -
  1. Let obj be ObjectCreate(%ObjectPrototype%).
    2. -
  2. Let status be the result of performing PropertyDefinitionEvaluation of PropertyDefinitionList with - argument obj.
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Return obj.
    5. -
-
LiteralPropertyName : IdentifierName
-
    -
  1. Return StringValue of IdentifierName.
    2. -
-
LiteralPropertyName : StringLiteral
-
    -
  1. Return a String value whose characters are the SV of the StringLiteral.
    2. -
-
LiteralPropertyName : NumericLiteral
-
    -
  1. Let nbr be the result of forming the value of the NumericLiteral.
    2. -
  2. Return ToString(nbr).
    3. -
-
ComputedPropertyName : [ AssignmentExpression ]
-
    -
  1. Let exprValue be the result of evaluating AssignmentExpression.
    2. -
  2. Let propName be GetValue(exprValue).
    3. -
  3. ReturnIfAbrupt(propName).
    4. -
  4. Return ToPropertyKey(propName).
    5. -
-
- -
-

12.2.5.9 Runtime Semantics: PropertyDefinitionEvaluation

- -

With parameter object.

- -

See also: 14.3.9, 14.4.16, B.3.1

- -
PropertyDefinitionList : PropertyDefinitionList , PropertyDefinition
-
    -
  1. Let status be the result of performing PropertyDefinitionEvaluation of PropertyDefinitionList with - argument object.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing PropertyDefinitionEvaluation of PropertyDefinition with argument - object.
    4. -
-
PropertyDefinition : IdentifierReference
-
    -
  1. Let propName be StringValue of IdentifierReference.
    2. -
  2. Let exprValue be the result of evaluating IdentifierReference.
    3. -
  3. ReturnIfAbrupt(exprValue).
    4. -
  4. Let propValue be GetValue(exprValue).
    5. -
  5. ReturnIfAbrupt(propValue).
    6. -
  6. Let desc be the Property Descriptor{[[Value]]: - propValue, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true}
    7. -
  7. Return DefinePropertyOrThrow(object, propName, - desc).
    8. -
-
PropertyDefinition : PropertyName : AssignmentExpression
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let exprValue be the result of evaluating AssignmentExpression.
    4. -
  4. Let propValue be GetValue(exprValue).
    5. -
  5. ReturnIfAbrupt(propValue).
    6. -
  6. If IsFunctionDefinition of AssignmentExpression is true, then -
      -
    1. Assert: propValue is an ECMAScript function object.
      2. -
    2. Let referencesSuper be the value of propValue’s [[NeedsSuper]] internal slot.
      3. -
    3. Let thisMode be the value of propValue’s [[ThisMode]] internal slot.
      4. -
    4. If thisMode is not lexical and referencesSuper is - true, then -
        -
      1. If propValue’s [[HomeObject]] internal slot is undefined, then -
          -
        1. Assert: AssignmentExpression is not a class definition - whose constructor references super.
          2. -
        2. Set propValue’s [[HomeObject]] internal slot to object.
          3. -
        3. Set propValue’s [[MethodName]] internal slot to propKey.
          4. -
        -
        2. -
      -
      5. -
    5. If IsAnonymousFunctionDefinition(AssignmentExpression) - is true, then -
        -
      1. SetFunctionName(propValue, propKey).
        2. -
      -
      6. -
    -
    7. -
  7. Let desc be the Property Descriptor{[[Value]]: - propValue, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true}
    8. -
  8. Return DefinePropertyOrThrow(object, propKey, - desc).
    9. -
- -

NOTE An alternative semantics for this production is given in B.3.1.

-
-
- -
-

12.2.6 Function Defining Expressions

- -

See 14.1 for PrimaryExpression : FunctionExpression .

- -

See 14.4 for PrimaryExpression : GeneratorExpression .

- -

See 14.5 for PrimaryExpression : ClassExpression .

-
- -
-
-

12.2.7 Generator Comprehensions

-

Syntax

- -
-
GeneratorComprehension[Yield] :
-
( Comprehension[?Yield] )
-
- -
-

NOTE The keyword yield may be used in IdentifierReference contexts within - a GeneratorComprehension contained in non-strict code. The following early - error rule ensures that a GeneratorComprehension never contains a YieldExpression.

-
-
- -
-

12.2.7.1 Static Semantics: Early Errors

-
GeneratorComprehension : ( Comprehension )
-
    -
  • It is a Syntax Error if Comprehension Contains - YieldExpression is true.
    • -
-
- -
-

12.2.7.2 Runtime Semantics: Evaluation

-
GeneratorComprehension : ( Comprehension )
-
    -
  1. If GeneratorComprehension is contained in strict mode code, then let - strict be true; otherwise let strict be false.
    2. -
  2. Let scope be the LexicalEnvironment of the running execution context.
    3. -
  3. Let parameters be the production: FormalParameters : [empty] .
    4. -
  4. Using Comprehension from the production that is being evaluated, let body be the supplemental - syntactic grammar production: GeneratorBody : - Comprehension .
    5. -
  5. Let closure be GeneratorFunctionCreate(Arrow, parameters, body, scope, strict).
    6. -
  6. Let prototype be ObjectCreate(%GeneratorPrototype%).
    7. -
  7. Perform MakeConstructor(closure, true, and prototype).
    8. -
  8. Let iterator be the result of calling the [[Call]] internal method of closure with undefined as - thisArgument and an empty List as - argumentsList.
    9. -
  9. Return iterator.
    10. -
- -
-

NOTE The GeneratorFunction object created in step 5 is not observable from ECMAScript code so - an implementation may choose to avoid its allocation and initialization. In that case, other semantically equivalent - means must be used to allocate and initialize the iterator object in step 8. In either case, the prototype - object created in step 6 must be created because it is potentially observable as the value of the iterator - object’s [[Prototype]] internal slot. If - strict is false and the Comprehesion contains any direct eval calls then any VarScopedDeclaration - bindings created by the evals are created in the VariableEnviornment of the function called in step 8.

-
-
-
- -
-
-

12.2.8 Regular Expression Literals

-

Syntax

- -

See 11.8.4.

-
- -
-

12.2.8.1 Static Semantics: Early Errors

-
PrimaryExpression : RegularExpressionLiteral
-
    -
  • -

    It is a Syntax Error if BodyText of RegularExpressionLiteral cannot be recognized using the goal symbol Pattern - of the ECMAScript RegExp grammar specified in 21.2.1.

    -
    • - -
  • -

    It is a Syntax Error if FlagText of RegularExpressionLiteral contains any character other than "g", "i", - "m", "u", or "y", or if it contains the same character more than once.

    -
    • -
-
- -
-

12.2.8.2 Runtime Semantics: Evaluation

-
PrimaryExpression : RegularExpressionLiteral
-
    -
  1. Let pattern be the string value consisting of the UTF-16Encoding of each code point of BodyText of - RegularExpressionLiteral.
    2. -
  2. Let flags be the string value consisting of the UTF-16Encoding of each code point of FlagText of - RegularExpressionLiteral.
    3. -
  3. Return RegExpCreate(pattern, flags).
    4. -
-
-
- -
-
-

12.2.9 - Template Literals

-

Syntax

- -
-
TemplateLiteral[Yield] :
-
NoSubstitutionTemplate
-
TemplateHead Expression[In, ?Yield] [Lexical goal InputElementTemplateTail] TemplateSpans[?Yield]
-
- -
-
TemplateSpans[Yield] :
-
TemplateTail
-
TemplateMiddleList[?Yield] [Lexical goal InputElementTemplateTail] TemplateTail
-
- -
-
TemplateMiddleList[Yield] :
-
TemplateMiddle Expression[In, ?Yield]
-
TemplateMiddleList[?Yield] [Lexical goal InputElementTemplateTail] TemplateMiddle Expression[In, ?Yield]
-
-
- -
-
-

12.2.9.1 Static Semantics

-
- -
-

12.2.9.1.1 Static Semantics: TemplateStrings

- -

With parameter raw.

- -
TemplateLiteral : NoSubstitutionTemplate
-
    -
  1. If raw is false, then -
      -
    1. Let string be the TV of NoSubstitutionTemplate.
      2. -
    -
    2. -
  2. Else, -
      -
    1. Let string be the TRV of NoSubstitutionTemplate.
      2. -
    -
    3. -
  3. Return a List containing the single element, - string.
    4. -
-
TemplateLiteral : TemplateHead Expression TemplateSpans
-
    -
  1. If raw is false, then -
      -
    1. Let head be the TV of TemplateHead.
      2. -
    -
    2. -
  2. Else, -
      -
    1. Let head be the TRV of TemplateHead.
      2. -
    -
    3. -
  3. Let tail be TemplateStrings of TemplateSpans with argument raw.
    4. -
  4. Return a List containing head followed by the - element, in order of tail.
    5. -
-
TemplateSpans : TemplateTail
-
    -
  1. If raw is false, then -
      -
    1. Let tail be the TV of TemplateTail.
      2. -
    -
    2. -
  2. Else, -
      -
    1. Let tail be the TRV of TemplateTail.
      2. -
    -
    3. -
  3. Return a List containing the single element, - tail.
    4. -
-
TemplateSpans : TemplateMiddleList TemplateTail
-
    -
  1. Let middle be TemplateStrings of TemplateMiddleList with argument raw.
    2. -
  2. If raw is false, then -
      -
    1. Let tail be the TV of TemplateTail.
      2. -
    -
    3. -
  3. Else, -
      -
    1. Let tail be the TRV of TemplateTail.
      2. -
    -
    4. -
  4. Return a List containing the elements, in order, of - middle followed by tail.
    5. -
-
TemplateMiddleList : TemplateMiddle Expression
-
    -
  1. If raw is false, then -
      -
    1. Let string be the TV of TemplateMiddle.
      2. -
    -
    2. -
  2. Else, -
      -
    1. Let string be the TRV of TemplateMiddle.
      2. -
    -
    3. -
  3. Return a List containing the single element, - string.
    4. -
-
TemplateMiddleList : TemplateMiddleList TemplateMiddle Expression
-
    -
  1. Let front be TemplateStrings of TemplateMiddleList with argument raw.
    2. -
  2. If raw is false, then -
      -
    1. Let last be the TV of TemplateMiddle.
      2. -
    -
    3. -
  3. Else, -
      -
    1. Let last be the TRV of TemplateMiddle.
      2. -
    -
    4. -
  4. Append last as the last element of the List - front.
    5. -
  5. Return front.
    6. -
-
-
- -
-
-

12.2.9.2 Runtime Semantics

-
- -
-

12.2.9.2.1 Runtime Semantics: - ArgumentListEvaluation

- -

See also: 12.3.6.1

- -
TemplateLiteral : NoSubstitutionTemplate
-
    -
  1. Let siteObj be the result of the abstract operation GetTemplateCallSite passing this TemplateLiteral - production as the argument.
    2. -
  2. Return a List containing the one element which is - siteObj.
    3. -
-
TemplateLiteral : TemplateHead Expression TemplateSpans
-
    -
  1. Let siteObj be the result of the abstract operation GetTemplateCallSite passing this TemplateLiteral - production as the argument.
    2. -
  2. Let firstSub be the result of evaluating Expression.
    3. -
  3. ReturnIfAbrupt(firstSub).
    4. -
  4. Let restSub be SubstitutionEvaluation of TemplateSpans.
    5. -
  5. ReturnIfAbrupt(restSub).
    6. -
  6. Assert: restSub is a List.
    7. -
  7. Return a List whose first element is siteObj, whose - second elements is firstSub, and whose subsequent elements are the elements of restSub, in order. - restSub may contain no elements.
    8. -
-
- -
-

12.2.9.2.2 Runtime Semantics: GetTemplateCallSite

- -

The abstract operation GetTemplateCallSite is called with a grammar - production, templateLiteral, as an argument. It performs the following steps:

- -
    -
  1. If a call site object for the source code corresponding to templateLiteral has already been created by a - previous call to this abstract operation, then -
      -
    1. Return that call site object.
      2. -
    -
    2. -
  2. Let cookedStrings be TemplateStrings of templateLiteral with argument false.
    3. -
  3. Let rawStrings be TemplateStrings of templateLiteral with argument true.
    4. -
  4. Let count be the number of elements in the List - cookedStrings.
    5. -
  5. Let siteObj be ArrayCreate(count).
    6. -
  6. Let rawObj be ArrayCreate(count).
    7. -
  7. Let index be 0.
    8. -
  8. Repeat while index < count -
      -
    1. Let prop be ToString(index).
      2. -
    2. Let cookedValue be the string value at 0-based position index of the List cookedStrings.
      3. -
    3. Call the [[DefineOwnProperty]] internal method of siteObj with arguments prop and - PropertyDescriptor{[[Value]]: cookedValue, [[Enumerable]]: true, [[Writable]]: false, - [[Configurable]]: false}.
      4. -
    4. Let rawValue be the string value at 0-based position index of the List rawStrings.
      5. -
    5. Call the [[DefineOwnProperty]] internal method of rawObj with arguments prop and - PropertyDescriptor{[[Value]]: rawValue, [[Enumerable]]: true, [[Writable]]: false, - [[Configurable]]: false}.
      6. -
    6. Let index be index+1.
      7. -
    -
    9. -
  9. Perform SetIntegrityLevel(rawObj, "frozen").
    10. -
  10. Call the [[DefineOwnProperty]] internal method of siteObj with arguments "raw" and - PropertyDescriptor{[[Value]]: rawObj, [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: false}.
    11. -
  11. Perform SetIntegrityLevel(siteObj, "frozen").
    12. -
  12. Remember an association between the source code corresponding to templateLiteral and siteObj such - that siteObj can be retrieve in subsequent calls to this abstract operation.
    13. -
  13. Return siteObj.
    14. -
- -
-

NOTE 1 The creation of a call site object cannot result in an abrupt completion.

-
- -
-

NOTE 2 Each TemplateLiteral in the program code is associated with a unique Template - call site object that is used in the evaluation of tagged Templates (12.2.9.2.4). The same call site object is used each - time a specific tagged Template is evaluated. Whether call site objects are created lazily upon first evaluation of - the TemplateLiteral or eagerly prior to first evaluation is an implementation choice that is not observable to - ECMAScript code.

-
- -
-

NOTE 3 Future editions of this specification may define additional non-enumerable - properties of call site objects.

-
-
- -
-

12.2.9.2.3 Runtime Semantics: SubstitutionEvaluation

-
TemplateSpans : TemplateTail
-
    -
  1. Return an empty List.
    2. -
-
TemplateSpans : TemplateMiddleList TemplateTail
-
    -
  1. Return the result of SubstitutionEvaluation of TemplateMiddleList.
    2. -
-
TemplateMiddleList : TemplateMiddle Expression
-
    -
  1. Let sub be the result of evaluating Expression.
    2. -
  2. ReturnIfAbrupt(sub).
    3. -
  3. Return a List containing only sub.
    4. -
-
TemplateMiddleList : TemplateMiddleList TemplateMiddle Expression
-
    -
  1. Let preceeding be the result of SubstitutionEvaluation of TemplateMiddleList .
    2. -
  2. ReturnIfAbrupt(preceeding).
    3. -
  3. Let next be the result of evaluating Expression.
    4. -
  4. ReturnIfAbrupt(next).
    5. -
  5. Append next as the last element of the List - preceeding.
    6. -
  6. Return preceeding.
    7. -
-
- -
-

12.2.9.2.4 Runtime Semantics: Evaluation

-
TemplateLiteral : NoSubstitutionTemplate
-
    -
  1. Return the string value whose elements are the TV of NoSubstitutionTemplate as defined in 11.8.6.
    2. -
-
TemplateLiteral : TemplateHead Expression TemplateSpans
-
    -
  1. Let head be the TV of TemplateHead as defined in 11.8.6.
    2. -
  2. Let sub be the result of evaluating Expression.
    3. -
  3. Let middle be ToString(sub).
    4. -
  4. ReturnIfAbrupt(middle).
    5. -
  5. Let tail be the result of evaluating TemplateSpans .
    6. -
  6. ReturnIfAbrupt(tail).
    7. -
  7. Return the string value whose elements are the code units of head followed by the code units of - tail.
    8. -
- -
-

NOTE The string conversion semantics applied to the Expression value are like - String.prototype.concat rather than the + - operator.

-
- -
TemplateSpans : TemplateTail
-
    -
  1. Let tail be the TV of TemplateTail as defined in 11.8.6.
    2. -
  2. Return the string whose elements are the code units of tail.
    3. -
-
TemplateSpans : TemplateMiddleList TemplateTail
-
    -
  1. Let head be the result of evaluating TemplateMiddleList.
    2. -
  2. ReturnIfAbrupt(head).
    3. -
  3. Let tail be the TV of TemplateTail as defined in 11.8.6.
    4. -
  4. Return the string whose elements are the elements of head followed by the elements of tail.
    5. -
-
TemplateMiddleList : TemplateMiddle Expression
-
    -
  1. Let head be the TV of TemplateMiddle as defined in 11.8.6.
    2. -
  2. Let sub be the result of evaluating Expression.
    3. -
  3. Let middle be ToString(sub).
    4. -
  4. ReturnIfAbrupt(middle).
    5. -
  5. Return the sequence of characters consisting of the code units of head followed by the elements of - middle.
    6. -
- -
-

NOTE The string conversion semantics applied to the Expression value are like - String.prototype.concat rather than the + - operator.

-
- -
TemplateMiddleList : TemplateMiddleList TemplateMiddle Expression
-
    -
  1. Let rest be the result of evaluating TemplateMiddleList .
    2. -
  2. ReturnIfAbrupt(rest).
    3. -
  3. Let middle be the TV of TemplateMiddle as defined in 11.8.6.
    4. -
  4. Let sub be the result of evaluating Expression.
    5. -
  5. Let last be ToString(sub).
    6. -
  6. ReturnIfAbrupt(last).
    7. -
  7. Return the sequence of characters consisting of the elements of rest followed by the code units of - middle followed by the elements of last.
    8. -
- -
-

NOTE The string conversion semantics applied to the Expression value are like - String.prototype.concat rather than the + - operator.

-
-
-
-
- -
-
-

12.2.10 - The Grouping Operator

-
- -
-

12.2.10.1 Static Semantics: Early Errors

-
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  • -

    It is a Syntax Error if the lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList cannot be parsed with no tokens left over using - ParenthesizedExpression as the goal symbol.

    -
    • - -
  • -

    All Early Errors rules for ParenthesizedExpression and its derived productions also apply - to the CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.

    -
    • -
-
- -
-

12.2.10.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
ParenthesizedExpression : ( Expression )
-
    -
  1. Return IsFunctionDefinition of Expression.
    2. -
-
- -
-

12.2.10.3 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
ParenthesizedExpression : ( Expression )
-
    -
  1. Return IsValidSimpleAssignmentTarget of Expression.
    2. -
-
- -
-

12.2.10.4 Runtime Semantics: Evaluation

-
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  1. Let expr be CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
    2. -
  2. Return the result of evaluating expr.
    3. -
-
ParenthesizedExpression : ( Expression )
-
    -
  1. Return the result of evaluating Expression. This may be of type Reference.
    2. -
- -
-

NOTE This algorithm does not apply GetValue to the result of - evaluating Expression. The principal motivation for this is so that operators such as delete and - typeof may be applied to parenthesized expressions.

-
-
-
-
- -
-
-

12.3 Left-Hand-Side Expressions

-

Syntax

- -
-
MemberExpression[Yield] :
-
[Lexical goal InputElementRegExp] PrimaryExpression[?Yield]
-
MemberExpression[?Yield] [ Expression[In, ?Yield] ]
-
MemberExpression[?Yield] . IdentifierName
-
MemberExpression[?Yield] TemplateLiteral[?Yield]
-
super [ Expression[In, ?Yield] ]
-
super . IdentifierName
-
new super Arguments[?Yield]
-
new MemberExpression[?Yield] Arguments[?Yield]
-
- -
-
NewExpression[Yield] :
-
MemberExpression[?Yield]
-
new NewExpression[?Yield]
-
new super
-
- -
-
CallExpression[Yield] :
-
MemberExpression[?Yield] Arguments[?Yield]
-
super Arguments[?Yield]
-
CallExpression[?Yield] Arguments[?Yield]
-
CallExpression[?Yield] [ Expression[In, ?Yield] ]
-
CallExpression[?Yield] . IdentifierName
-
CallExpression[?Yield] TemplateLiteral[?Yield]
-
- -
-
Arguments[Yield] :
-
( )
-
( ArgumentList[?Yield] )
-
- -
-
ArgumentList[Yield] :
-
AssignmentExpression[In, ?Yield]
-
... AssignmentExpression[In, ?Yield]
-
ArgumentList[?Yield] , AssignmentExpression[In, ?Yield]
-
ArgumentList[?Yield] , ... AssignmentExpression[In, ?Yield]
-
- -
-
LeftHandSideExpression[Yield] :
-
NewExpression[?Yield]
-
CallExpression[?Yield]
-
-
- -
-
-

12.3.1 Static Semantics

-
- -
-

12.3.1.1 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.2.5.2, 14.1.4, 14.2.3, 14.4.3, 14.5.4

- -
MemberExpression : MemberExpression . IdentifierName
-
    -
  1. If MemberExpression Contains symbol is true, return true.
    2. -
  2. If symbol is a ReservedWord, return false.
    3. -
  3. If symbol is an Identifier and StringValue of symbol is the same value as the StringValue of - IdentifierName, return true;
    4. -
  4. Return false.
    5. -
-
MemberExpression : super . IdentifierName
-
    -
  1. If symbol is the ReservedWord super, return true.
    2. -
  2. If symbol is a ReservedWord, return false.
    3. -
  3. If symbol is an Identifier and StringValue of symbol is the same value as the StringValue of - IdentifierName, return true;
    4. -
  4. Return false.
    5. -
-
CallExpression : CallExpression . IdentifierName
-
    -
  1. If CallExpression Contains symbol is true, return true.
    2. -
  2. If symbol is a ReservedWord, return false.
    3. -
  3. If symbol is an Identifier and StringValue of symbol is the same value as the StringValue of - IdentifierName, return true;
    4. -
  4. Return false.
    5. -
-
- -
-

12.3.1.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
MemberExpression :
-
MemberExpression [ Expression ]
-
MemberExpression . IdentifierName
-
MemberExpression TemplateLiteral
-
super [ Expression ]
-
super . IdentifierName
-
new super Arguments
-
new MemberExpression Arguments
-
- -
-
NewExpression :
-
new NewExpression
-
new super
-
- -
-
CallExpression :
-
MemberExpression Arguments
-
super Arguments
-
CallExpression Arguments
-
CallExpression [ Expression ]
-
CallExpression . IdentifierName
-
CallExpression TemplateLiteral
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.3.1.3 Static Semantics: IsIdentifierRef

- -

See also: 12.2.0.3.

- -
-
LeftHandSideExpression :
-
CallExpression
-
- -
-
MemberExpression :
-
MemberExpression [ Expression ]
-
MemberExpression . IdentifierName
-
MemberExpression TemplateLiteral
-
super [ Expression ]
-
super . IdentifierName
-
new super Arguments
-
new MemberExpression Arguments
-
- -
-
NewExpression :
-
new NewExpression
-
new super
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.3.1.4 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
CallExpression :
-
CallExpression [ Expression ]
-
CallExpression . IdentifierName
-
- -
-
MemberExpression :
-
MemberExpression [ Expression ]
-
MemberExpression . IdentifierName
-
super [ Expression ]
-
super . IdentifierName
-
- -
    -
  1. Return true.
    2. -
- -
-
CallExpression :
-
MemberExpression Arguments
-
super Arguments
-
CallExpression Arguments
-
CallExpression TemplateLiteral
-
- -
-
NewExpression :
-
new NewExpression
-
new super
-
- -
-
MemberExpression :
-
MemberExpression TemplateLiteral
-
new super Arguments
-
new MemberExpression Arguments
-
- -
    -
  1. Return false.
    2. -
-
-
- -
-
-

12.3.2 - Property Accessors

- -
-

NOTE Properties are accessed by name, using either the dot notation:

-
- -
MemberExpression . IdentifierName
CallExpression . IdentifierName
- -

or the bracket notation:

- -
MemberExpression [ Expression ]
CallExpression [ Expression ]
- -

The dot notation is explained by the following syntactic conversion:

- -
MemberExpression . IdentifierName
- -

is identical in its behaviour to

- -
MemberExpression [ <identifier-name-string> ]
- -

and similarly

- -
CallExpression . IdentifierName
- -

is identical in its behaviour to

- -
CallExpression [ <identifier-name-string> ]
- -

where <identifier-name-string> is a string literal containing the same sequence of characters after - processing of Unicode escape sequences as the IdentifierName.

-
- -
-

12.3.2.1 Runtime Semantics: Evaluation

-
MemberExpression : MemberExpression [ Expression ]
-
    -
  1. Let baseReference be the result of evaluating MemberExpression.
    2. -
  2. Let baseValue be GetValue(baseReference).
    3. -
  3. ReturnIfAbrupt(baseValue).
    4. -
  4. Let propertyNameReference be the result of evaluating Expression.
    5. -
  5. Let propertyNameValue be GetValue(propertyNameReference).
    6. -
  6. ReturnIfAbrupt(propertyNameValue).
    7. -
  7. Let bv be CheckObjectCoercible(baseValue).
    8. -
  8. ReturnIfAbrupt(bv).
    9. -
  9. Let propertyNameString be ToString(propertyNameValue).
    10. -
  10. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    11. -
  11. Return a value of type Reference whose base value is bv and - whose referenced name is propertyNameString, and whose strict reference flag is strict.
    12. -
-
CallExpression : CallExpression [ Expression ]
- -

Is evaluated in exactly the same manner as MemberExpression : MemberExpression [ Expression - ] except that the contained CallExpression is evaluated in step - 1.

-
-
- -
-
-

12.3.3 The - new Operator

-
- -
-

12.3.3.1 Runtime Semantics: Evaluation

-
NewExpression : new NewExpression
-
    -
  1. Let ref be the result of evaluating NewExpression.
    2. -
  2. Let constructor be GetValue(ref).
    3. -
  3. ReturnIfAbrupt(constructor).
    4. -
  4. If IsConstructor(constructor) is false, throw a TypeError - exception.
    5. -
  5. Let thisCall be this NewExpression.
    6. -
  6. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    7. -
  7. If tailCall is true, then perform the PrepareForTailCall - abstract operation.
    8. -
  8. Let result be the result of calling the [[Construct]] internal method on constructor with an empty List as the argument.
    9. -
  9. Assert: If tailCall is true, the above call of [[Construct]] - will not return here, but instead evaluation will continue as if the following return has already occurred.
    10. -
  10. Return result.
    11. -
-
MemberExpression : new MemberExpression Arguments
-
    -
  1. Let ref be the result of evaluating MemberExpression.
    2. -
  2. Let constructor be GetValue(ref).
    3. -
  3. ReturnIfAbrupt(constructor).
    4. -
  4. Let argList be the result of evaluating Arguments, producing a List of argument values (12.3.6).
    5. -
  5. ReturnIfAbrupt(argList).
    6. -
  6. If IsConstructor (constructor) is false, throw a TypeError - exception.
    7. -
  7. Let thisCall be this MemberExpression.
    8. -
  8. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    9. -
  9. If tailCall is true, then perform the PrepareForTailCall - abstract operation.
    10. -
  10. Let result be the result of calling the [[Construct]] internal method on constructor, passing - argList as the argument.
    11. -
  11. Assert: If tailCall is true, the above call of [[Construct]] - will not return here, but instead evaluation will continue as if the following return has already occurred.
    12. -
  12. Return result.
    13. -
-
-
- -
-
-

12.3.4 - Function Calls

-
- -
-

12.3.4.1 Runtime Semantics: Evaluation

-
CallExpression : MemberExpression Arguments
-
    -
  1. Let ref be the result of evaluating MemberExpression.
    2. -
  2. If MemberExpression consists solely of the IdentifierName eval, then -
      -
    1. check if direct eval
      2. -
    2. Return EvaluateCall(ref, Arguments, false).
      3. -
    -
    3. -
  3. Let thisCall be this CallExpression.
    4. -
  4. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    5. -
  5. Return EvaluateCall(ref, Arguments, tailCall).
    6. -
-
CallExpression : CallExpression Arguments
-
    -
  1. Let ref be the result of evaluating CallExpression.
    2. -
  2. Let thisCall be this CallExpression
    3. -
  3. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    4. -
  4. Return EvaluateCall(ref, Arguments, tailCall).
    5. -
-
- -
-

12.3.4.2 Runtime Semantics: EvaluateCall

- -

The abstract operation EvaluateCall takes as arguments a value ref, and a syntactic grammar production - arguments, and a Boolean argument tailPosition. It performs the following steps:

- -
    -
  1. Let func be GetValue(ref).
    2. -
  2. ReturnIfAbrupt(func).
    3. -
  3. Let argList be ArgumentListEvaluation(arguments).
    4. -
  4. ReturnIfAbrupt(argList).
    5. -
  5. If IsCallable(func) is false, throw a TypeError exception.
    6. -
  6. If Type(ref) is Reference, then -
      -
    1. If IsPropertyReference(ref) is true, then -
        -
      1. Let thisValue be GetThisValue(ref).
        2. -
      -
      2. -
    2. Else, the base of ref is an Environment Record -
        -
      1. Let thisValue be the result of calling the WithBaseObject concrete method of GetBase(ref).
        2. -
      -
      3. -
    -
    7. -
  7. Else Type(ref) is not Reference, -
      -
    1. Let thisValue be undefined.
      2. -
    -
    8. -
  8. If tailPosition is true, then perform the PrepareForTailCall - abstract operation.
    9. -
  9. Let result be the result of calling the [[Call]] internal method on func, passing thisValue as - the thisArgument and argList as the argumentsList.
    10. -
  10. Assert: If tailPosition is true, the above call will not - return here, but instead evaluation will continue as if the following return has already occurred.
    11. -
  11. Assert: If result is not an abrupt completion then Type(result) is an ECMAScript language type
    12. -
  12. Return result.
    13. -
-
-
- -
-
-

12.3.5 The - super Keyword

-
- -
-

12.3.5.1 Static Semantics: Early Errors

- -
-
MemberExpression :
-
super [ Expression ]
-
super . IdentifierName
-
new super Arguments
-
NewExpression : new super
-
CallExpression : super Arguments
-
- -
    -
  • -

    It is a Syntax Error if the source code parsed with this production is global code that is not eval code.

    -
    • - -
  • -

    It is a Syntax Error if the source code parsed with this production is eval code and the source code is not being - processed by a direct call to eval that is contained in function code.

    -
    • -
-
- -
-

12.3.5.2 Runtime Semantics: Evaluation

-
MemberExpression : super [ Expression ]
-
    -
  1. Let propertyNameReference be the result of evaluating Expression.
    2. -
  2. Let propertyNameValue be GetValue(propertyNameReference).
    3. -
  3. Let propertyKey be ToPropertyKey(propertyNameValue).
    4. -
  4. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    5. -
  5. Return MakeSuperReference(propertyKey, strict).
    6. -
-
MemberExpression : super . IdentifierName
-
    -
  1. Let propertyKey be StringValue of IdentifierName.
    2. -
  2. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    3. -
  3. Return MakeSuperReference(propertyKey, strict).
    4. -
-
MemberExpression : new super Arguments
-
    -
  1. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    2. -
  2. Let ref be MakeSuperReference(undefined, strict).
    3. -
  3. Let constructor be GetValue(ref).
    4. -
  4. ReturnIfAbrupt(constructor).
    5. -
  5. Let argList be the result of evaluating Arguments, producing a List of argument values (12.3.6).
    6. -
  6. ReturnIfAbrupt(argList).
    7. -
  7. If IsConstructor (constructor) is false, throw a TypeError - exception.
    8. -
  8. Let thisCall be this MemberExpression.
    9. -
  9. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    10. -
  10. If tailCall is true, then perform the PrepareForTailCall - abstract operation.
    11. -
  11. Let result be the result of calling the [[Construct]] internal method on constructor, passing - argList as the argument.
    12. -
  12. Assert: If tailCall is true, the above call of [[Construct]] - will not return here, but instead evaluation will continue as if the following return has already occurred.
    13. -
  13. Return result.
    14. -
-
NewExpression : new super
-
    -
  1. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    2. -
  2. Let ref be MakeSuperReference(undefined, strict).
    3. -
  3. Let constructor be GetValue(ref).
    4. -
  4. ReturnIfAbrupt(constructor).
    5. -
  5. Let argList be a new empty List.
    6. -
  6. ReturnIfAbrupt(argList).
    7. -
  7. If IsConstructor (constructor) is false, throw a TypeError - exception.
    8. -
  8. Let thisCall be this NewExpression.
    9. -
  9. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    10. -
  10. If tailCall is true, then perform the PrepareForTailCall - abstract operation.
    11. -
  11. Let result be the result of calling the [[Construct]] internal method on constructor, passing - argList as the argument.
    12. -
  12. Assert: If tailCall is true, the above call of [[Construct]] - will not return here, but instead evaluation will continue as if the following return has already occurred.
    13. -
  13. Return result.
    14. -
-
CallExpression : super Arguments
-
    -
  1. If the code matched by the syntactic production that is being evaluated is strict - mode code, let strict be true, else let strict be false.
    2. -
  2. Let ref be MakeSuperReference(undefined, strict).
    3. -
  3. ReturnIfAbrupt(ref).
    4. -
  4. Let thisCall be this CallExpression.
    5. -
  5. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    6. -
  6. Return EvaluateCall(ref, Arguments, tailCall).
    7. -
-
- -
-

12.3.5.3 Runtime Semantics: MakeSuperReference(propertyKey, strict)

- -

The abstract operation MakeSuperReference with arguments propertyKey and strict performs the - following steps:

- -
    -
  1. Let env be GetThisEnvironment( ).
    2. -
  2. If the result of calling the HasSuperBinding concrete method of env is false, then throw a - ReferenceError exception.
    3. -
  3. Let actualThis be the result of calling the GetThisBinding concrete method of env.
    4. -
  4. Let baseValue be the result of calling the GetSuperBase concrete method of - env.
    5. -
  5. Let bv be CheckObjectCoercible(baseValue).
    6. -
  6. ReturnIfAbrupt(bv).
    7. -
  7. If propertyKey is undefined, then -
      -
    1. Let propertyKey be the result of calling the GetMethodName concrete - method of env.
      2. -
    2. If propertyKey is undefined, then throw a ReferenceError exception.
      3. -
    -
    8. -
  8. Return a value of type Reference that is a Super Reference whose base value is bv, whose referenced name is - propertyKey, whose thisValue is actualThis, and whose strict reference flag is strict.
    9. -
-
-
- -
-
-

12.3.6 - Argument Lists

- -
-

NOTE The evaluation of an argument list produces a List of values (see - 6.2.1).

-
-
- -
-

12.3.6.1 Runtime Semantics: - ArgumentListEvaluation

- -

See also: 12.2.9.2.1

- -
Arguments : ( )
-
    -
  1. Return an empty List.
    2. -
-
ArgumentList : AssignmentExpression
-
    -
  1. Let ref be the result of evaluating AssignmentExpression.
    2. -
  2. Let arg be GetValue(ref).
    3. -
  3. ReturnIfAbrupt(arg).
    4. -
  4. Return a List whose sole item is arg.
    5. -
-
ArgumentList : ... AssignmentExpression
-
    -
  1. Let list be an empty List.
    2. -
  2. Let spreadRef be the result of evaluating AssignmentExpression.
    3. -
  3. Let spreadObj be GetValue(spreadRef).
    4. -
  4. ReturnIfAbrupt(spreadObj).
    5. -
  5. If Type(spreadObj) is not Object, then throw a - TypeError exception.
    6. -
  6. Let iterator be GetIterator(spreadObj).
    7. -
  7. ReturnIfAbrupt(iterator).
    8. -
  8. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return list.
      4. -
    4. Let nextArg be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextArg).
      6. -
    6. Append nextArg as the last element of list.
      7. -
    -
    9. -
-
ArgumentList : ArgumentList , AssignmentExpression
-
    -
  1. Let precedingArgs be the result of evaluating ArgumentList.
    2. -
  2. ReturnIfAbrupt(precedingArgs).
    3. -
  3. Let ref be the result of evaluating AssignmentExpression.
    4. -
  4. Let arg be GetValue(ref).
    5. -
  5. ReturnIfAbrupt(arg).
    6. -
  6. Return a List whose length is one greater than the length of - precedingArgs and whose items are the items of precedingArgs, in order, followed at the end by - arg which is the last item of the new list.
    7. -
-
ArgumentList : ArgumentList , ... AssignmentExpression
-
    -
  1. Let precedingArgs be the result of evaluating ArgumentList.
    2. -
  2. Let spreadRef be the result of evaluating AssignmentExpression.
    3. -
  3. Let spreadObj be GetValue(spreadRef).
    4. -
  4. ReturnIfAbrupt(spreadObj).
    5. -
  5. If Type(spreadObj) is not Object, then throw a - TypeError exception.
    6. -
  6. Let iterator be GetIterator(spreadObj).
    7. -
  7. ReturnIfAbrupt(iterator).
    8. -
  8. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return precedingArgs.
      4. -
    4. Let nextArg be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextArg).
      6. -
    6. Append nextArg as the last element of precedingArgs.
      7. -
    -
    9. -
-
-
- -
-
-

12.3.7 - Tagged Templates

-
- -
-

12.3.7.1 Runtime Semantics: Evaluation

-
MemberExpression : MemberExpression TemplateLiteral
-
    -
  1. Let tagRef be the result of evaluating MemberExpression.
    2. -
  2. Let thisCall be this MemberExpression.
    3. -
  3. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    4. -
  4. Return EvaluateCall(tagRef, TemplateLiteral, tailCall).
    5. -
-
CallExpression : CallExpression TemplateLiteral
-
    -
  1. Let tagRef be the result of evaluating CallExpression.
    2. -
  2. Let thisCall be this CallExpression.
    3. -
  3. Let tailCall be IsInTailPosition(thisCall). (See 14.6.1)
    4. -
  4. Return EvaluateCall(tagRef, TemplateLiteral, tailCall).
    5. -
-
-
-
- -
-
-

12.4 - Postfix Expressions

-

Syntax

- -
-
PostfixExpression[Yield] :
-
LeftHandSideExpression[?Yield]
-
LeftHandSideExpression[?Yield] [no LineTerminator here] ++
-
LeftHandSideExpression[?Yield] [no LineTerminator here] --
-
-
- -
-

12.4.1 Static Semantics: Early Errors

- -
-
PostfixExpression :
-
LeftHandSideExpression ++
-
LeftHandSideExpression --
-
- -
    -
  • -

    It is an early Reference Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.

    -
    • -
-
- -
-

12.4.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8

- -
-
PostfixExpression :
-
LeftHandSideExpression ++
-
LeftHandSideExpression --
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.4.3 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
PostfixExpression :
-
LeftHandSideExpression ++
-
LeftHandSideExpression --
-
- -
    -
  1. Return false.
    2. -
-
- -
-
-

12.4.4 Postfix Increment Operator

-
- -
-

12.4.4.1 Runtime Semantics: Evaluation

-
PostfixExpression : LeftHandSideExpression ++
-
    -
  1. Let lhs be the result of evaluating LeftHandSideExpression.
    2. -
  2. Let oldValue be ToNumber(GetValue(lhs)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. Let newValue be the result of adding the value 1 to oldValue, using the same rules as for - the + operator (see 12.7.5).
    5. -
  5. Let status be PutValue(lhs, newValue).
    6. -
  6. ReturnIfAbrupt(status).
    7. -
  7. Return oldValue.
    8. -
-
-
- -
-
-

12.4.5 Postfix Decrement Operator

-
- -
-

12.4.5.1 Runtime Semantics: Evaluation

-
PostfixExpression : LeftHandSideExpression --
-
    -
  1. Let lhs be the result of evaluating LeftHandSideExpression.
    2. -
  2. Let oldValue be ToNumber(GetValue(lhs)).
    3. -
  3. Let newValue be the result of subtracting the value 1 from oldValue, using the same rules - as for the - operator (12.7.5).
    4. -
  4. Let status be PutValue(lhs, newValue).
    5. -
  5. ReturnIfAbrupt(status).
    6. -
  6. Return oldValue.
    7. -
-
-
-
- -
-
-

12.5 Unary - Operators

-

Syntax

- -
-
UnaryExpression[Yield] :
-
PostfixExpression[?Yield]
-
delete UnaryExpression[?Yield]
-
void UnaryExpression[?Yield]
-
typeof UnaryExpression[?Yield]
-
++ UnaryExpression[?Yield]
-
-- UnaryExpression[?Yield]
-
+ UnaryExpression[?Yield]
-
- UnaryExpression[?Yield]
-
~ UnaryExpression[?Yield]
-
! UnaryExpression[?Yield]
-
-
- -
-

12.5.1 Static Semantics: Early Errors

- -
-
UnaryExpression :
-
++ UnaryExpression
-
-- UnaryExpression
-
- -
    -
  • -

    It is an early Reference Error if IsValidSimpleAssignmentTarget of UnaryExpression is false.

    -
    • -
-
- -
-

12.5.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
UnaryExpression :
-
delete UnaryExpression
-
void UnaryExpression
-
typeof UnaryExpression
-
++ UnaryExpression
-
-- UnaryExpression
-
+ UnaryExpression
-
- UnaryExpression
-
~ UnaryExpression
-
! UnaryExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.5.3 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
UnaryExpression :
-
delete UnaryExpression
-
void UnaryExpression
-
typeof UnaryExpression
-
++ UnaryExpression
-
-- UnaryExpression
-
+ UnaryExpression
-
- UnaryExpression
-
~ UnaryExpression
-
! UnaryExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-
-

12.5.4 The - delete Operator

-
- -
-

12.5.4.1 Static Semantics: Early Errors

-
UnaryExpression : delete UnaryExpression
-
    -
  • -

    It is a Syntax Error if the UnaryExpression is contained in strict code and the derived UnaryExpression is PrimaryExpression : - IdentifierReference.

    -
    • - -
  • -

    It is a Syntax Error if the derived UnaryExpression is
    PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
    and derives a - production that, if used in place of UnaryExpression, would produce a Syntax Error according to these - rules. This rule is recursively applied.

    -
    • -
- -
-

NOTE The last rule means that expressions such as
delete - (((foo)))
produce early errors because of recursive application of the first rule.

-
-
- -
-

12.5.4.2 Runtime Semantics: Evaluation

-
UnaryExpression : delete UnaryExpression
-
    -
  1. Let ref be the result of evaluating UnaryExpression.
    2. -
  2. ReturnIfAbrupt(ref).
    3. -
  3. If Type(ref) is not Reference, return true.
    4. -
  4. If IsUnresolvableReference(ref) is true, then, -
      -
    1. Assert: IsStrictReference(ref) is false.
      2. -
    2. Return true.
      3. -
    -
    5. -
  5. If IsPropertyReference(ref) is true, then -
      -
    1. If IsSuperReference(ref), then throw a - ReferenceError exception.
      2. -
    2. Let deleteStatus be the result of calling the [[Delete]] internal method on ToObject(GetBase(ref)), - providing GetReferencedName(ref) as the argument.
      3. -
    3. ReturnIfAbrupt(deleteStatus).
      4. -
    4. If deleteStatus is false and IsStrictReference(ref) is true, then throw a - TypeError exception.
      5. -
    5. Return deleteStatus.
      6. -
    -
    6. -
  6. Else ref is a Reference to an Environment Record binding, -
      -
    1. Let bindings be GetBase(ref).
      2. -
    2. Return the result of calling the DeleteBinding concrete method of bindings, providing GetReferencedName(ref) as the argument.
      3. -
    -
    7. -
- -
-

NOTE When a delete operator occurs within strict - mode code, a SyntaxError exception is thrown if its UnaryExpression is a direct reference to a - variable, function argument, or function name. In addition, if a delete operator occurs within strict mode code and the property to be deleted has the attribute { [[Configurable]]: - false }, a TypeError exception is thrown.

-
-
-
- -
-
-

12.5.5 The - void Operator

-
- -
-

12.5.5.1 Runtime Semantics: Evaluation

-
UnaryExpression : void UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let status be GetValue(expr).
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Return undefined.
    5. -
- -
-

NOTE GetValue must be called even though its value is not used - because it may have observable side-effects.

-
-
-
- -
-
-

12.5.6 The - typeof Operator

-
- -
-

12.5.6.1 Runtime Semantics: Evaluation

-
UnaryExpression : typeof UnaryExpression
-
    -
  1. Let val be the result of evaluating UnaryExpression.
    2. -
  2. If Type(val) is Reference, then -
      -
    1. If IsUnresolvableReference(val) is true, return - "undefined".
      2. -
    2. Let val be GetValue(val).
      3. -
    -
    3. -
  3. ReturnIfAbrupt(val).
    4. -
  4. Return a String according to Table 33.
    5. -
- -
-
Table 33 — typeof Operator Results
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Type of valResult
Undefined"undefined"
Null"object"
Boolean"boolean"
Number"number"
String"string"
Symbol"symbol"
Object (ordinary and does not implement [[Call]])"object"
Object (standard exotic and does not implement [[Call]])"object"
Object (implements [[Call]])"function"
Object (non-standard exotic and does not implement [[Call]])Implementation-defined. Must not be "undefined", "boolean", "number", "symbol", or "string".
-
- -
-

NOTE Implementations are discouraged from defining new typeof result values for - non-standard exotic objects. If possible "object"should be used for such objects.

-
-
-
- -
-
-

12.5.7 Prefix Increment Operator

-
- -
-

12.5.7.1 Runtime Semantics: Evaluation

-
UnaryExpression : ++ UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let oldValue be ToNumber(GetValue(expr)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. Let newValue be the result of adding the value 1 to oldValue, using the same rules as for - the + operator (see 12.7.5).
    5. -
  5. Let status be PutValue(expr, newValue).
    6. -
  6. ReturnIfAbrupt(status).
    7. -
  7. Return newValue.
    8. -
-
-
- -
-
-

12.5.8 Prefix Decrement Operator

-
- -
-

12.5.8.1 Runtime Semantics: Evaluation

-
UnaryExpression : -- UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let oldValue be ToNumber(GetValue(expr)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. Let newValue be the result of subtracting the value 1 from oldValue, using the same - rules as for the - operator (see - 12.7.5).
    5. -
  5. Let status be PutValue(expr, newValue).
    6. -
  6. ReturnIfAbrupt(status).
    7. -
  7. Return newValue.
    8. -
-
-
- -
-
-

12.5.9 - Unary + Operator

- -
-

NOTE The unary + operator converts its operand to Number type.

-
-
- -
-

12.5.9.1 Runtime Semantics: Evaluation

-
UnaryExpression : + UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Return ToNumber(GetValue(expr)).
    3. -
-
-
- -
-
-

12.5.10 Unary - Operator

- -
-

NOTE The unary - operator converts its operand to Number type and then negates - it. Negating +0 produces −0, and negating −0 produces +0.

-
-
- -
-

12.5.10.1 Runtime Semantics: Evaluation

-
UnaryExpression : - UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let oldValue be ToNumber(GetValue(expr)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. If oldValue is NaN, return NaN.
    5. -
  5. Return the result of negating oldValue; that is, compute a Number with the same magnitude but opposite - sign.
    6. -
-
-
- -
-
-

12.5.11 Bitwise NOT Operator ( ~ )

-
- -
-

12.5.11.1 Runtime Semantics: Evaluation

-
UnaryExpression : ~ UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let oldValue be ToInt32(GetValue(expr)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. Return the result of applying bitwise complement to oldValue. The result is a signed 32-bit integer.
    5. -
-
-
- -
-
-

12.5.12 Logical NOT Operator ( ! )

-
- -
-

12.5.12.1 Runtime Semantics: Evaluation

-
UnaryExpression : ! UnaryExpression
-
    -
  1. Let expr be the result of evaluating UnaryExpression.
    2. -
  2. Let oldValue be ToBoolean(GetValue(expr)).
    3. -
  3. ReturnIfAbrupt(oldValue).
    4. -
  4. If oldValue is true, return false.
    5. -
  5. Return true.
    6. -
-
-
-
- -
-
-

12.6 - Multiplicative Operators

-

Syntax

- -
-
MultiplicativeExpression[Yield] :
-
UnaryExpression[?Yield]
-
MultiplicativeExpression[?Yield] * UnaryExpression[?Yield]
-
MultiplicativeExpression[?Yield] / UnaryExpression[?Yield]
-
MultiplicativeExpression[?Yield] % UnaryExpression[?Yield]
-
-
- -
-

12.6.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
MultiplicativeExpression :
-
MultiplicativeExpression * UnaryExpression
-
MultiplicativeExpression / UnaryExpression
-
MultiplicativeExpression % UnaryExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.6.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
MultiplicativeExpression :
-
MultiplicativeExpression * UnaryExpression
-
MultiplicativeExpression / UnaryExpression
-
MultiplicativeExpression % UnaryExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-
-

12.6.3 Runtime Semantics: Evaluation

- -

The production MultiplicativeExpression : MultiplicativeExpression @ UnaryExpression , where - @ stands for one of the operators in the above definitions, is evaluated as follows:

- -
    -
  1. Let left be the result of evaluating MultiplicativeExpression.
    2. -
  2. Let leftValue be GetValue(left).
    3. -
  3. ReturnIfAbrupt(leftValue).
    4. -
  4. Let right be the result of evaluating UnaryExpression.
    5. -
  5. Let rightValue be GetValue(right).
    6. -
  6. Let lnum be ToNumber(leftValue).
    7. -
  7. ReturnIfAbrupt(lnum).
    8. -
  8. Let rnum be ToNumber(rightValue).
    9. -
  9. ReturnIfAbrupt(rnum).
    10. -
  10. Return the result of applying the specified operation (*, /, or %) to lnum and rnum. See the Notes - below 12.6.3.1, 12.6.3.2, - 12.6.3.3.
    11. -
-
- -
-

12.6.3.1 Applying the * Operator

- -

The * operator performs multiplication, producing the product of its operands. Multiplication is - commutative. Multiplication is not always associative in ECMAScript, because of finite precision.

- -

The result of a floating-point multiplication is governed by the rules of IEEE 754 binary double-precision - arithmetic:

- -
    -
  • -

    If either operand is NaN, the result is NaN.

    -
    • - -
  • -

    The sign of the result is positive if both operands have the same sign, negative if the operands have different - signs.

    -
    • - -
  • -

    Multiplication of an infinity by a zero results in NaN.

    -
    • - -
  • -

    Multiplication of an infinity by an infinity results in an infinity. The sign is determined by the rule already - stated above.

    -
    • - -
  • -

    Multiplication of an infinity by a finite nonzero value results in a signed infinity. The sign is determined by the - rule already stated above.

    -
    • - -
  • -

    In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the - nearest representable value using IEEE 754 round-to-nearest mode. If the magnitude is too large to represent, the - result is then an infinity of appropriate sign. If the magnitude is too small to represent, the result is then a zero - of appropriate sign. The ECMAScript language requires support of gradual underflow as defined by IEEE 754.

    -
    • -
-
- -
-

12.6.3.2 Applying the / Operator

- -

The / operator performs division, producing the quotient of its operands. The left operand is the dividend - and the right operand is the divisor. ECMAScript does not perform integer division. The operands and result of all - division operations are double-precision floating-point numbers. The result of division is determined by the specification - of IEEE 754 arithmetic:

- -
    -
  • -

    If either operand is NaN, the result is NaN.

    -
    • - -
  • -

    The sign of the result is positive if both operands have the same sign, negative if the operands have different - signs.

    -
    • - -
  • -

    Division of an infinity by an infinity results in NaN.

    -
    • - -
  • -

    Division of an infinity by a zero results in an infinity. The sign is determined by the rule already stated - above.

    -
    • - -
  • -

    Division of an infinity by a nonzero finite value results in a signed infinity. The sign is determined by the rule - already stated above.

    -
    • - -
  • -

    Division of a finite value by an infinity results in zero. The sign is determined by the rule already stated - above.

    -
    • - -
  • -

    Division of a zero by a zero results in NaN; division of zero by any other finite value results in zero, - with the sign determined by the rule already stated above.

    -
    • - -
  • -

    Division of a nonzero finite value by a zero results in a signed infinity. The sign is determined by the rule - already stated above.

    -
    • - -
  • -

    In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the quotient is computed - and rounded to the nearest representable value using IEEE 754 round-to-nearest mode. If the magnitude is too large to - represent, the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small - to represent, the operation underflows and the result is a zero of the appropriate sign. The ECMAScript language - requires support of gradual underflow as defined by IEEE 754.

    -
    • -
-
- -
-

12.6.3.3 Applying the % Operator

- -

The % operator yields the remainder of its operands from an implied division; the left operand is the - dividend and the right operand is the divisor.

- -
-

NOTE In C and C++, the remainder operator accepts only integral operands; in ECMAScript, it - also accepts floating-point operands.

-
- -

The result of a floating-point remainder operation as computed by the % operator is not the same as the - “remainder” operation defined by IEEE 754. The IEEE 754 “remainder” operation computes the - remainder from a rounding division, not a truncating division, and so its behaviour is not analogous to that of the usual - integer remainder operator. Instead the ECMAScript language defines % on floating-point operations to behave - in a manner analogous to that of the Java integer remainder operator; this may be compared with the C library function - fmod.

- -

The result of an ECMAScript floating-point remainder operation is determined by the rules of IEEE arithmetic:

- -
    -
  • -

    If either operand is NaN, the result is NaN.

    -
    • - -
  • -

    The sign of the result equals the sign of the dividend.

    -
    • - -
  • -

    If the dividend is an infinity, or the divisor is a zero, or both, the result is NaN.

    -
    • - -
  • -

    If the dividend is finite and the divisor is an infinity, the result equals the dividend.

    -
    • - -
  • -

    If the dividend is a zero and the divisor is nonzero and finite, the result is the same as the dividend.

    -
    • - -
  • -

    In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the floating-point - remainder r from a dividend n and a divisor d is defined by the mathematical relation r = n − (d × q) - where q is an integer that is negative only if n/d is negative and positive only if n/d is positive, and whose - magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of n and d. r is - computed and rounded to the nearest representable value using IEEE 754 round-to-nearest mode.

    -
    • -
-
-
-
- -
-
-

12.7 - Additive Operators

-

Syntax

- -
-
AdditiveExpression[Yield] :
-
MultiplicativeExpression[?Yield]
-
AdditiveExpression[?Yield] + MultiplicativeExpression[?Yield]
-
AdditiveExpression[?Yield] - MultiplicativeExpression[?Yield]
-
-
- -
-

12.7.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
AdditiveExpression :
-
AdditiveExpression + MultiplicativeExpression
-
AdditiveExpression - MultiplicativeExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.7.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
AdditiveExpression :
-
AdditiveExpression + MultiplicativeExpression
-
AdditiveExpression - MultiplicativeExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-
-

12.7.3 The Addition operator ( + )

- -
-

NOTE The addition operator either performs string concatenation or numeric addition.

-
-
- -
-

12.7.3.1 Runtime Semantics: Evaluation

-
AdditiveExpression : AdditiveExpression + MultiplicativeExpression
-
    -
  1. Let lref be the result of evaluating AdditiveExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating MultiplicativeExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lprim be ToPrimitive(lval).
    8. -
  8. ReturnIfAbrupt(lprim).
    9. -
  9. Let rprim be ToPrimitive(rval).
    10. -
  10. ReturnIfAbrupt(rprim).
    11. -
  11. If Type(lprim) is String or Type(rprim) is String, then -
      -
    1. Return the String that is the result of concatenating ToString(lprim) - followed by ToString(rprim)
      2. -
    -
    12. -
  12. Return the result of applying the addition operation to ToNumber(lprim) and ToNumber(rprim). See the Note below 12.7.5.
    13. -
- -
-

NOTE 1 No hint is provided in the calls to ToPrimitive in - steps 7 and 9. All standard objects except Date objects handle the absence of a hint as if the hint Number were given; - Date objects handle the absence of a hint as if the hint String were given. Exotic objects may handle the absence of a - hint in some other manner.

-
- -
-

NOTE 2 Step 11 differs from step 5 of the Abstract Relational Comparison algorithm (7.2.8), by using the logical-or operation instead of the logical-and operation.

-
-
-
- -
-
-

12.7.4 The Subtraction Operator ( - )

-
- -
-

12.7.4.1 Runtime Semantics: Evaluation

-
AdditiveExpression : AdditiveExpression - MultiplicativeExpression
-
    -
  1. Let lref be the result of evaluating AdditiveExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating MultiplicativeExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lnum be ToNumber(lval).
    8. -
  8. ReturnIfAbrupt(lnum).
    9. -
  9. Let rnum be ToNumber(rval).
    10. -
  10. ReturnIfAbrupt(rnum).
    11. -
  11. Return the result of applying the subtraction operation to lnum and rnum. See the note below 12.7.5.
    12. -
-
-
- -
-

12.7.5 Applying the Additive Operators to Numbers

- -

The + operator performs addition when applied to two operands of numeric type, producing the sum of the - operands. The - operator performs subtraction, producing the difference of two numeric operands.

- -

Addition is a commutative operation, but not always associative.

- -

The result of an addition is determined using the rules of IEEE 754 binary double-precision arithmetic:

- -
    -
  • -

    If either operand is NaN, the result is NaN.

    -
    • - -
  • -

    The sum of two infinities of opposite sign is NaN.

    -
    • - -
  • -

    The sum of two infinities of the same sign is the infinity of that sign.

    -
    • - -
  • -

    The sum of an infinity and a finite value is equal to the infinite operand.

    -
    • - -
  • -

    The sum of two negative zeroes is −0. The sum of two positive zeroes, or of two zeroes of opposite sign, - is +0.

    -
    • - -
  • -

    The sum of a zero and a nonzero finite value is equal to the nonzero operand.

    -
    • - -
  • -

    The sum of two nonzero finite values of the same magnitude and opposite sign is +0.

    -
    • - -
  • -

    In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, and the operands have the same - sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using IEEE 754 - round-to-nearest mode. If the magnitude is too large to represent, the operation overflows and the result is then an - infinity of appropriate sign. The ECMAScript language requires support of gradual underflow as defined by IEEE 754.

    -
    • -
- -
-

NOTE The - operator performs subtraction when applied to two operands of numeric - type, producing the difference of its operands; the left operand is the minuend and the right operand is the subtrahend. - Given numeric operands a and b, it is always the case that a–b produces the same - result as a +(–b).

-
-
-
- -
-
-

12.8 - Bitwise Shift Operators

-

Syntax

- -
-
ShiftExpression[Yield] :
-
AdditiveExpression[?Yield]
-
ShiftExpression[?Yield] << AdditiveExpression[?Yield]
-
ShiftExpression[?Yield] >> AdditiveExpression[?Yield]
-
ShiftExpression[?Yield] >>> AdditiveExpression[?Yield]
-
-
- -
-

12.8.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
ShiftExpression :
-
ShiftExpression << AdditiveExpression
-
ShiftExpression >> AdditiveExpression
-
ShiftExpression >>> AdditiveExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.8.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
ShiftExpression :
-
ShiftExpression << AdditiveExpression
-
ShiftExpression >> AdditiveExpression
-
ShiftExpression >>> AdditiveExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-
-

12.8.3 - The Left Shift Operator ( << )

- -
-

NOTE Performs a bitwise left shift operation on the left operand by the amount specified by - the right operand.

-
-
- -
-

12.8.3.1 Runtime Semantics: Evaluation

-
ShiftExpression : ShiftExpression << AdditiveExpression
-
    -
  1. Let lref be the result of evaluating ShiftExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating AdditiveExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lnum be ToInt32(lval).
    8. -
  8. ReturnIfAbrupt(lnum).
    9. -
  9. Let rnum be ToUint32(rval).
    10. -
  10. ReturnIfAbrupt(rnum).
    11. -
  11. Let shiftCount be the result of masking out all but the least significant 5 bits of rnum, that is, - compute rnum & 0x1F.
    12. -
  12. Return the result of left shifting lnum by shiftCount bits. The result is a signed 32-bit - integer.
    13. -
-
-
- -
-
-

12.8.4 The Signed Right Shift Operator ( >> )

- -
-

NOTE Performs a sign-filling bitwise right shift operation on the left operand by the amount - specified by the right operand.

-
-
- -
-

12.8.4.1 Runtime Semantics: Evaluation

-
ShiftExpression : ShiftExpression >> AdditiveExpression
-
    -
  1. Let lref be the result of evaluating ShiftExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating AdditiveExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lnum be ToInt32(lval).
    8. -
  8. ReturnIfAbrupt(lnum).
    9. -
  9. Let rnum be ToUint32(rval).
    10. -
  10. ReturnIfAbrupt(rnum).
    11. -
  11. Let shiftCount be the result of masking out all but the least significant 5 bits of rnum, that is, - compute rnum & 0x1F.
    12. -
  12. Return the result of performing a sign-extending right shift of lnum by shiftCount bits. The most - significant bit is propagated. The result is a signed 32-bit integer.
    13. -
-
-
- -
-
-

12.8.5 The Unsigned Right Shift Operator ( >>> )

- -
-

NOTE Performs a zero-filling bitwise right shift operation on the left operand by the amount - specified by the right operand.

-
-
- -
-

12.8.5.1 Runtime Semantics: Evaluation

-
ShiftExpression : ShiftExpression >>> AdditiveExpression
-
    -
  1. Let lref be the result of evaluating ShiftExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating AdditiveExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lnum be ToUint32(lval).
    8. -
  8. ReturnIfAbrupt(lnum).
    9. -
  9. Let rnum be ToUint32(rval).
    10. -
  10. ReturnIfAbrupt(rnum).
    11. -
  11. Let shiftCount be the result of masking out all but the least significant 5 bits of rnum, that is, - compute rnum & 0x1F.
    12. -
  12. Return the result of performing a zero-filling right shift of lnum by shiftCount bits. Vacated bits - are filled with zero. The result is an unsigned 32-bit integer.
    13. -
-
-
-
- -
-
-

12.9 - Relational Operators

- -
-

NOTE The result of evaluating a relational operator is always of type Boolean, reflecting - whether the relationship named by the operator holds between its two operands.

-
- -

Syntax

- -
-
RelationalExpression[In, Yield] :
-
ShiftExpression[?Yield]
-
RelationalExpression[?In, ?Yield] < ShiftExpression[?Yield]
-
RelationalExpression[?In, ?Yield] > ShiftExpression[?Yield]
-
RelationalExpression[?In, ?Yield] <= ShiftExpression[? Yield]
-
RelationalExpression[?In, ?Yield] >= ShiftExpression[?Yield]
-
RelationalExpression[?In, ?Yield] instanceof ShiftExpression[?Yield]
-
[+In] RelationalExpression[In, ?Yield] in ShiftExpression[?Yield]
-
- -
-

NOTE The [In] grammar parameter is needed to avoid confusing the in operator in a - relational expression with the in operator in a for statement.

-
-
- -
-

12.9.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
RelationalExpression :
-
RelationalExpression < ShiftExpression
-
RelationalExpression > ShiftExpression
-
RelationalExpression <= ShiftExpression
-
RelationalExpression >= ShiftExpression
-
RelationalExpression instanceof ShiftExpression
-
RelationalExpression in ShiftExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.9.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
RelationalExpression :
-
RelationalExpression < ShiftExpression
-
RelationalExpression > ShiftExpression
-
RelationalExpression <= ShiftExpression
-
RelationalExpression >= ShiftExpression
-
RelationalExpression instanceof ShiftExpression
-
RelationalExpression in ShiftExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.9.3 Runtime Semantics: Evaluation

-
RelationalExpression : RelationalExpression < ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. Let r be the result of performing Abstract Relational Comparison lval < rval. (see 7.2.8)
    7. -
  7. ReturnIfAbrupt(r).
    8. -
  8. If r is undefined, return false. Otherwise, return r.
    9. -
-
RelationalExpression : RelationalExpression > ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. Let r be the result of performing Abstract Relational Comparison rval < lval with - LeftFirst equal to false.
    7. -
  7. ReturnIfAbrupt(r).
    8. -
  8. If r is undefined, return false. Otherwise, return r.
    9. -
-
RelationalExpression : RelationalExpression <= ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. Let r be the result of performing Abstract Relational Comparison rval < lval with - LeftFirst equal to false.
    7. -
  7. ReturnIfAbrupt(r).
    8. -
  8. If r is true or undefined, return false. Otherwise, return true.
    9. -
-
RelationalExpression : RelationalExpression >= ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. Let r be the result of performing Abstract Relational Comparison lval < rval.
    7. -
  7. ReturnIfAbrupt(r).
    8. -
  8. If r is true or undefined, return false. Otherwise, return true.
    9. -
-
RelationalExpression : RelationalExpression instanceof ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Return InstanceofOperator(lval, rval).
    8. -
-
RelationalExpression : RelationalExpression in ShiftExpression
-
    -
  1. Let lref be the result of evaluating RelationalExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating ShiftExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. If Type(rval) is not Object, throw a TypeError - exception.
    8. -
  8. Return HasProperty(rval, ToPropertyKey(lval)).
    9. -
-
- -
-

12.9.4 - Runtime Semantics: InstanceofOperator(O, C)

- -

The abstract operation InstanceofOperator(O, C) - implements the generic algorithm for determining if an object O inherits from the inheritance path defined by - constructor C. This abstract operation performs the following steps:

- -
    -
  1. If Type(C) is not Object, throw a TypeError - exception.
    2. -
  2. Let instOfHandler be GetMethod(C,@@hasInstance).
    3. -
  3. ReturnIfAbrupt(instOfHandler).
    4. -
  4. If instOfHandler is not undefined, then -
      -
    1. Let result be the result of calling the [[Call]] internal method of instOfHandler passing C - as thisArgument and a new List containing O as - argumentsList.
      2. -
    2. Return ToBoolean(result).
      3. -
    -
    5. -
  5. If IsCallable(C) is false, then throw a TypeError exception.
    6. -
  6. Return OrdinaryHasInstance(C, O).
    7. -
- -
-

NOTE Steps 5 and 6 provide compatibility with previous editions of ECMAScript that did not use - a @@hasInstance method to define the instanceof operator semantics. If a function object does not define or - inherit @@hasInstance it uses the default instanceof semantics.

-
-
-
- -
-
-

12.10 - Equality Operators

- -
-

NOTE The result of evaluating an equality operator is always of type Boolean, reflecting - whether the relationship named by the operator holds between its two operands.

-
- -

Syntax

- -
-
EqualityExpression[In, Yield] :
-
RelationalExpression[?In, ?Yield]
-
EqualityExpression[?In, ?Yield] == RelationalExpression[?In, ?Yield]
-
EqualityExpression[?In, ?Yield] != RelationalExpression[?In, ?Yield]
-
EqualityExpression[?In, ?Yield] === RelationalExpression[?In, ?Yield]
-
EqualityExpression[?In, ?Yield] !== RelationalExpression[?In, ?Yield]
-
-
- -
-

12.10.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
-
EqualityExpression :
-
EqualityExpression == RelationalExpression
-
EqualityExpression != RelationalExpression
-
EqualityExpression === RelationalExpression
-
EqualityExpression !== RelationalExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.10.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -
-
EqualityExpression :
-
EqualityExpression == RelationalExpression
-
EqualityExpression != RelationalExpression
-
EqualityExpression === RelationalExpression
-
EqualityExpression !== RelationalExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.10.3 Runtime Semantics: Evaluation

-
EqualityExpression : EqualityExpression == RelationalExpression
-
    -
  1. Let lref be the result of evaluating EqualityExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating RelationalExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Return the result of performing Abstract Equality Comparison rval == lval.
    8. -
-
EqualityExpression : EqualityExpression != RelationalExpression
-
    -
  1. Let lref be the result of evaluating EqualityExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating RelationalExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let r be the result of performing Abstract Equality Comparison rval == lval.
    8. -
  8. If r is true, return false. Otherwise, return true.
    9. -
-
EqualityExpression : EqualityExpression === RelationalExpression
-
    -
  1. Let lref be the result of evaluating EqualityExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval)
    4. -
  4. Let rref be the result of evaluating RelationalExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Return the result of performing Strict Equality Comparison rval === lval.
    8. -
-
EqualityExpression : EqualityExpression !== RelationalExpression
-
    -
  1. Let lref be the result of evaluating EqualityExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating RelationalExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let r be the result of performing Strict Equality Comparison rval === lval.
    8. -
  8. If r is true, return false. Otherwise, return true.
    9. -
- -
-

NOTE 1 Given the above definition of equality:

- -
    -
  • String comparison can be forced by: "" + a == "" + b.
    • -
  • Numeric comparison can be forced by: +a == +b.
    • -
  • Boolean comparison can be forced by: !a == !b.
    • -
-
- -
-

NOTE 2 The equality operators maintain the following invariants:

- -
    -
  • A != B is equivalent to !(A == - B).
    • -
  • A == B is equivalent to B == A, except - in the order of evaluation of A and B.
    • -
-
- -
-

NOTE 3 The equality operator is not always transitive. For example, there might be two distinct - String objects, each representing the same String value; each String object would be considered equal to the String value - by the == operator, but the two String objects would not be equal to each other. For Example:

- -
    -
  • new String("a") == "a" and "a" == new - String("a")are both true.
    • -
  • new String("a") == new String("a") is false.
    • -
-
- -
-

NOTE 4 Comparison of Strings uses a simple equality test on sequences of code unit values. - There is no attempt to use the more complex, semantically oriented definitions of character or string equality and - collating order defined in the Unicode specification. Therefore Strings values that are canonically equal according to the - Unicode standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized - form.

-
-
-
- -
-
-

12.11 Binary Bitwise Operators

-

Syntax

- -
-
BitwiseANDExpression[In, Yield] :
-
EqualityExpression[?In, ?Yield]
-
BitwiseANDExpression[?In, ?Yield] & EqualityExpression[?In, ?Yield]
-
- -
-
BitwiseXORExpression[In, Yield] :
-
BitwiseANDExpression[?In, ?Yield]
-
BitwiseXORExpression[?In, ?Yield] ^ BitwiseANDExpression[?In, ?Yield]
-
- -
-
BitwiseORExpression[In, Yield] :
-
BitwiseXORExpression[?In, ?Yield]
-
BitwiseORExpression[?In, ?Yield] | BitwiseXORExpression[?In, ?Yield]
-
-
- -
-

12.11.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -

BitwiseANDExpression : BitwiseANDExpression & EqualityExpression

- -

BitwiseXORExpression : BitwiseXORExpression ^ BitwiseANDExpression

- -
BitwiseORExpression : BitwiseORExpression | BitwiseXORExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.11.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.

- -

BitwiseANDExpression : BitwiseANDExpression & EqualityExpression

- -

BitwiseXORExpression : BitwiseXORExpression ^ BitwiseANDExpression

- -
BitwiseORExpression : BitwiseORExpression | BitwiseXORExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.11.3 Runtime Semantics: Evaluation

- -

The production A : A @ B, where @ is one of the bitwise operators in the productions above, is evaluated as - follows:

- -
    -
  1. Let lref be the result of evaluating A.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating B.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let lnum be ToInt32(lval).
    8. -
  8. ReturnIfAbrupt(lnum).
    9. -
  9. Let rnum be ToInt32(rval).
    10. -
  10. ReturnIfAbrupt(rnum).
    11. -
  11. Return the result of applying the bitwise operator @ to lnum and rnum. The result is a signed 32 bit - integer.
    12. -
-
-
- -
-
-

12.12 Binary Logical Operators

-

Syntax

- -
-
LogicalANDExpression[In, Yield] :
-
BitwiseORExpression[?In, ?Yield]
-
LogicalANDExpression[?In, ?Yield] && BitwiseORExpression[?In, ?Yield]
-
- -
-
LogicalORExpression[In, Yield] :
-
LogicalANDExpression[?In, ?Yield]
-
LogicalORExpression[?In, ?Yield] || LogicalANDExpression[?In, ?Yield]
-
- -
-

NOTE The value produced by a && or || operator is not - necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.

-
-
- -
-

12.12.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -

LogicalANDExpression : LogicalANDExpression && BitwiseORExpression

- -
LogicalORExpression : LogicalORExpression || LogicalANDExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.12.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.13.2, 12.14.3, 12.15.2.

- -

LogicalANDExpression : LogicalANDExpression && BitwiseORExpression

- -
LogicalORExpression : LogicalORExpression || LogicalANDExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.12.3 Runtime Semantics: Evaluation

-
LogicalANDExpression : LogicalANDExpression && BitwiseORExpression
-
    -
  1. Let lref be the result of evaluating LogicalANDExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. Let lbool be ToBoolean(lval).
    4. -
  4. ReturnIfAbrupt(lbool).
    5. -
  5. If lbool is false, return lval.
    6. -
  6. Let rref be the result of evaluating BitwiseORExpression.
    7. -
  7. Return GetValue(rref).
    8. -
-
LogicalORExpression : LogicalORExpression || LogicalANDExpression
-
    -
  1. Let lref be the result of evaluating LogicalORExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. Let lbool be ToBoolean(lval).
    4. -
  4. ReturnIfAbrupt(lbool).
    5. -
  5. If lbool is true, return lval.
    6. -
  6. Let rref be the result of evaluating LogicalANDExpression.
    7. -
  7. Return GetValue(rref).
    8. -
-
-
- -
-
-

12.13 - Conditional Operator ( ? : )

-

Syntax

- -
-
ConditionalExpression[In, Yield] :
-
LogicalORExpression[?In, ?Yield]
-
LogicalORExpression[?In,?Yield] ? AssignmentExpression[In, ?Yield] : AssignmentExpression[?In, ?Yield]
-
- -
-

NOTE The grammar for a ConditionalExpression in ECMAScript is slightly different from - that in C and Java, which each allow the second subexpression to be an Expression but restrict the third expression - to be a ConditionalExpression. The motivation for this difference in ECMAScript is to allow an assignment - expression to be governed by either arm of a conditional and to eliminate the confusing and fairly useless case of a comma - expression as the centre expression.

-
-
- -
-

12.13.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
ConditionalExpression : LogicalORExpression ? AssignmentExpression : AssignmentExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.13.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.14.3, 12.15.2.

- -
ConditionalExpression : LogicalORExpression ? AssignmentExpression : AssignmentExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.13.3 Runtime Semantics: Evaluation

-
ConditionalExpression : LogicalORExpression ? AssignmentExpression : AssignmentExpression
-
    -
  1. Let lref be the result of evaluating LogicalORExpression.
    2. -
  2. Let lval be ToBoolean(GetValue(lref)).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. If lval is true, then -
      -
    1. Let trueRef be the result of evaluating the first AssignmentExpression.
      2. -
    2. Return GetValue(trueRef).
      3. -
    -
    5. -
  5. Else -
      -
    1. Let falseRef be the result of evaluating the second AssignmentExpression.
      2. -
    2. Return GetValue(falseRef).
      3. -
    -
    6. -
-
-
- -
-
-

12.14 - Assignment Operators

-

Syntax

- -
-
AssignmentExpression[In, Yield] :
-
ConditionalExpression[?In, ?Yield]
-
[+Yield] YieldExpression[?In]
-
ArrowFunction[?In, ?Yield]
-
LeftHandSideExpression[?Yield] = AssignmentExpression[?In, ?Yield]
-
LeftHandSideExpression[?Yield] AssignmentOperator AssignmentExpression[?In, ?Yield]
-
- -
AssignmentOperator : one of
- -
- - - - - - - - - - - - - - -
*=/=%=+=-=<<=>>=>>>=&=^=|=
-
-
- -
-

12.14.1 Static Semantics: Early Errors

-
AssignmentExpression : LeftHandSideExpression = AssignmentExpression
-
    -
  • -

    It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and the lexical token sequence matched by - LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.

    -
    • - -
  • -

    If LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression can be parsed with no tokens left over using AssignmentPattern as the goal symbol then the following rules are not applied. Instead, the Early - Error rules for AssignmentPattern are used.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is an IdentifierReference that can be statically determined to always resolve to a declarative environment record binding and the resolved binding is an - immutable binding.

    -
    • - -
  • -

    It is an early Reference Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget of - LeftHandSideExpression is false.

    -
    • -
-
AssignmentExpression : LeftHandSideExpression AssignmentOperator AssignmentExpression
-
    -
  • -

    It is a Syntax Error if the LeftHandSideExpression is an IdentifierReference that can be statically determined to always resolve to a declarative environment record binding and the resolved binding is an - immutable binding.

    -
    • - -
  • -

    It is an early Reference Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.

    -
    • -
-
- -
-

12.14.2 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.15.1, 14.1.11, 14.4.8, 14.5.8.

- -
AssignmentExpression : ArrowFunction
-
    -
  1. Return true.
    2. -
- -
-
AssignmentExpression :
-
YieldExpression
-
LeftHandSideExpression = AssignmentExpression
-
LeftHandSideExpression AssignmentOperator AssignmentExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.14.3 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.15.2.

- -
-
AssignmentExpression :
-
YieldExpression
-
ArrowFunction
-
LeftHandSideExpression = AssignmentExpression
-
LeftHandSideExpression AssignmentOperator AssignmentExpression
-
- -
    -
  1. Return false.
    2. -
-
- -
-

12.14.4 Runtime Semantics: Evaluation

- -

AssignmentExpression[In, Yield] : LeftHandSideExpression[?Yield] = AssignmentExpression[?In, ?Yield]

- -
    -
  1. If LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral then -
      -
    1. Let lref be the result of evaluating LeftHandSideExpression.
      2. -
    2. ReturnIfAbrupt(lref).
      3. -
    3. Let rref be the result of evaluating AssignmentExpression.
      4. -
    4. Let rval be GetValue(rref).
      5. -
    5. If IsAnonymousFunctionDefinition(AssignmentExpression) and - IsIdentifierRef of LeftHandSideExpression are both true, then -
        -
      1. Let hasNameProperty be HasOwnProperty(rval, - "name").
        2. -
      2. ReturnIfAbrupt(hasNameProperty).
        3. -
      3. If hasNameProperty is false, then -
          -
        1. SetFunctionName(rval, GetReferencedName(lref)).
          2. -
        -
        4. -
      -
      6. -
    6. Let status be PutValue(lref, rval).
      7. -
    7. ReturnIfAbrupt(status).
      8. -
    8. Return rval.
      9. -
    -
    2. -
  2. Let AssignmentPattern be the parse of the source code corresponding to LeftHandSideExpression using - AssignmentPattern[?Yield] as the goal symbol.
    3. -
  3. Let rref be the result of evaluating AssignmentExpression.
    4. -
  4. Let rval be GetValue(rref).
    5. -
  5. ReturnIfAbrupt(rval).
    6. -
  6. If Type(rval) is not Object, then throw a TypeError - exception.
    7. -
  7. Let status be the result of performing DestructuringAssignmentEvaluation of AssignmentPattern using - rval as the argument.
    8. -
  8. ReturnIfAbrupt(status).
    9. -
  9. Return rval.
    10. -
-
AssignmentExpression : LeftHandSideExpression AssignmentOperator AssignmentExpression
-
    -
  1. Let lref be the result of evaluating LeftHandSideExpression.
    2. -
  2. Let lval be GetValue(lref).
    3. -
  3. ReturnIfAbrupt(lval).
    4. -
  4. Let rref be the result of evaluating AssignmentExpression.
    5. -
  5. Let rval be GetValue(rref).
    6. -
  6. ReturnIfAbrupt(rval).
    7. -
  7. Let operator be the @ where AssignmentOperator is @=
    8. -
  8. Let r be the result of applying operator @ to lval and rval.
    9. -
  9. Let status be PutValue(lref, r).
    10. -
  10. ReturnIfAbrupt(status).
    11. -
  11. Return r.
    12. -
- -
-

NOTE When an assignment occurs within strict mode code, it - is an runtime error if lref in step 1.f.of the first algorithm or step 9 of the second algorithm it is an - unresolvable reference. If it is, a ReferenceError exception is thrown. The LeftHandSide also may not be a - reference to a data property with the attribute value {[[Writable]]:false}, to an accessor property with the - attribute value {[[Set]]:undefined}, nor to a non-existent property of an object for which the IsExtensible predicate returns the value false. In these cases a TypeError - exception is thrown.

-
-
- -
-
-

12.14.5 Destructuring Assignment

-

Supplemental Syntax

- -

In certain circumstances when processing the production AssignmentExpression - : LeftHandSideExpression = AssignmentExpression the following grammar is used to refine the interpretation of LeftHandSideExpression.

- -
-
AssignmentPattern[Yield] :
-
ObjectAssignmentPattern[?Yield]
-
ArrayAssignmentPattern[?Yield]
-
- -
-
ObjectAssignmentPattern[Yield] :
-
{ }
-
{ AssignmentPropertyList[?Yield] }
-
{ AssignmentPropertyList[?Yield] , }
-
- -
-
ArrayAssignmentPattern[Yield] :
-
[ Elisionopt AssignmentRestElement[?Yield]opt ]
-
[ AssignmentElementList[?Yield] ]
-
[ AssignmentElementList[?Yield] , Elisionopt AssignmentRestElement[?Yield]opt ]
-
- -
-
AssignmentPropertyList[Yield] :
-
AssignmentProperty[?Yield]
-
AssignmentPropertyList[?Yield] , AssignmentProperty[?Yield]
-
- -
-
AssignmentElementList[Yield] :
-
AssignmentElisionElement[?Yield]
-
AssignmentElementList[?Yield] , AssignmentElisionElement[?Yield]
-
- -
-
AssignmentElisionElement[Yield] :
-
Elisionopt AssignmentElement[?Yield]
-
- -
-
AssignmentProperty[Yield] :
-
IdentifierReference[?Yield] Initializer[In,?Yield]opt
-
PropertyName : AssignmentElement[?Yield]
-
- -
-
AssignmentElement[Yield] :
-
DestructuringAssignmentTarget[?Yield] Initializer[In,?Yield]opt
-
- -
-
AssignmentRestElement[Yield] :
-
... DestructuringAssignmentTarget[?Yield]
-
- -
-
DestructuringAssignmentTarget[Yield] :
-
LeftHandSideExpression[?Yield]
-
-
- -
-

12.14.5.1 Static Semantics: Early Errors

-
AssignmentProperty : IdentifierReference Initializeropt
-
    -
  • -

    It is a Syntax Error if IsValidSimpleAssignment of IdentifierReference is false.

    -
    • - -
  • -

    It is a Syntax Error if IdentifierReference statically resolves to a immutable - binding.

    -
    • -
-
AssignmentRestElement : ... DestructuringAssignmentTarget
-
    -
  • -

    It is a Syntax Error if IsValidSimpleAssignmentTarget of DestructuringAssignmentTarget is false.

    -
    • -
-
DestructuringAssignmentTarget : LeftHandSideExpression
-
    -
  • -

    It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched - by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget(LeftHandSideExpression) is false.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is an IdentifierReference that can be statically determined to always resolve to a declarative environment record binding and the resolved binding is an - immutable binding.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is CoverParenthesizedExpressionAndArrowParameterList : - ( Expression ) and Expression derives a production that would produce a Syntax Error according to these rules if that - production is substituted for LeftHandSideExpression. This rule is recursively applied.

    -
    • -
- -
-

NOTE The last rule means that the other rules are applied even if multiple levels of nested - parentheses surround Expression.

-
-
- -
-

12.14.5.2 Runtime Semantics: DestructuringAssignmentEvaluation

- -

with parameter obj

- -
ObjectAssignmentPattern : { }
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
ArrayAssignmentPattern : [ ]
-
    -
  1. Let iterator be GetIterator(obj).
    2. -
  2. ReturnIfAbrupt(iterator).
    3. -
  3. Return NormalCompletion(empty).
    4. -
-
ArrayAssignmentPattern : [ Elision ]
-
    -
  1. Let iterator be GetIterator(obj).
    2. -
  2. ReturnIfAbrupt(iterator).
    3. -
  3. Return the result of performing IteratorDestructuringAssignmentEvaluation of Elision with iterator as - the argument.
    4. -
-
ArrayAssignmentPattern : [ Elisionopt AssignmentRestElement ]
-
    -
  1. Let iterator be GetIterator(obj).
    2. -
  2. ReturnIfAbrupt(iterator).
    3. -
  3. If Elision is present, then -
      -
    1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    4. -
  4. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentRestElement with - iterator as the argument.
    5. -
-
ArrayAssignmentPattern : [ AssignmentElementList ]
-
    -
  1. Let iterator be GetIterator(obj).
    2. -
  2. ReturnIfAbrupt(iterator).
    3. -
  3. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentElementList using - iterator as the argument.
    4. -
-
ArrayAssignmentPattern : [ AssignmentElementList , Elisionopt AssignmentRestElementopt ]
-
    -
  1. Let iterator be GetIterator(obj).
    2. -
  2. ReturnIfAbrupt(iterator).
    3. -
  3. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of - AssignmentElementList using iterator as the argument.
    4. -
  4. ReturnIfAbrupt(status).
    5. -
  5. If Elision is present, then -
      -
    1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    6. -
  6. If AssignmentRestElement is not present, then return status.
    7. -
  7. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentRestElement with - iterator as the argument.
    8. -
-
AssignmentPropertyList : AssignmentPropertyList , AssignmentProperty
-
    -
  1. Let status be the result of performing DestructuringAssignmentEvaluation for AssignmentPropertyList - using obj as the argument.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing DestructuringAssignmentEvaluation for AssignmentProperty using obj as - the argument.
    4. -
-
AssignmentProperty : IdentifierReference Initializeropt
-
    -
  1. Let P be StringValue of IdentifierReference.
    2. -
  2. Let v be Get(obj, P).
    3. -
  3. ReturnIfAbrupt(v).
    4. -
  4. If Initializeropt is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue).
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    -
    5. -
  5. Let lref be ResolveBinding(P).
    6. -
  6. Return PutValue(lref,v).
    7. -
-
AssignmentProperty : PropertyName : AssignmentElement
-
    -
  1. Let name be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(name).
    3. -
  3. Return the result of performing KeyedDestructuringAssignmentEvaluation of AssignmentElement with obj - and name as the arguments.
    4. -
-
- -
-

12.14.5.3 Runtime Semantics: IteratorDestructuringAssignmentEvaluation

- -

with parameters iterator

- -
AssignmentElementList : AssignmentElisionElement
-
    -
  1. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentElisionElement using - iterator as the argument.
    2. -
-
AssignmentElementList : AssignmentElementList , AssignmentElisionElement
-
    -
  1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of - AssignmentElementList using iterator as the argument.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentElisionElement using - iterator as the argument.
    4. -
-
AssignmentElisionElement : AssignmentElement
-
    -
  1. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentElement with - iterator as the argument.
    2. -
-
AssignmentElisionElement : Elision AssignmentElement
-
    -
  1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorDestructuringAssignmentEvaluation of AssignmentElement with - iterator as the argument.
    4. -
-
Elision : ,
-
    -
  1. Return IteratorStep(iterator).
    2. -
-
Elision : Elision ,
-
    -
  1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return IteratorStep(iterator).
    4. -
- -

AssignmentElement[Yield] : DestructuringAssignmentTarget Initializeropt

- -
    -
  1. If DestructuringAssignmentTarget is neither an ObjectLiteral nor an ArrayLiteral then -
      -
    1. Let lref be the result of evaluating DestructuringAssignmentTarget.
      2. -
    2. ReturnIfAbrupt(lref).
      3. -
    -
    2. -
  2. Let next be IteratorStep(iterator).
    3. -
  3. ReturnIfAbrupt(next).
    4. -
  4. If next is false, then let v be undefined
    5. -
  5. Else -
      -
    1. Let v be IteratorValue(next).
      2. -
    2. ReturnIfAbrupt(v).
      3. -
    -
    6. -
  6. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue)
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    -
    7. -
  7. If DestructuringAssignmentTarget is an ObjectLiteral or an ArrayLiteral then -
      -
    1. Let nestedAssignmentPattern be the parse of the source code corresponding to - DestructuringAssignmentTarget using either AssignmentPattern or - AssignmentPattern[Yield] as the goal symbol depending upon whether this - AssignmentElement has the Yield parameter.
      2. -
    2. If Type(v) is not Object, then throw a - TypeError exception.
      3. -
    3. Return the result of performing DestructuringAssignmentEvaluation of nestedAssignmentPattern with - v as the argument.
      4. -
    -
    8. -
  8. Return PutValue(lref,v).
    9. -
- -
-

NOTE Left to right evaluation order is maintained by evaluating a - DestructuringAssignmentTarget that is not a destructuring pattern prior to accessing the iterator or evaluating - the Initializer.

-
- -
AssignmentRestElement : ... DestructuringAssignmentTarget
-
    -
  1. Let lref be the result of evaluating DestructuringAssignmentTarget.
    2. -
  2. ReturnIfAbrupt(lref).
    3. -
  3. Let A be ArrayCreate(0).
    4. -
  4. Let n=0;
    5. -
  5. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then -
        -
      1. Return PutValue(lref, A).
        2. -
      -
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let defineStatus be CreateDataPropertyOrThrow(A, ToString(ToUint32(n)), nextValue).
      7. -
    7. ReturnIfAbrupt(defineStatus).
      8. -
    8. Increment n by 1.
      9. -
    -
    6. -
-
- -
-

12.14.5.4 Runtime Semantics: KeyedDestructuringAssignmentEvaluation

- -

with parameters obj and propertyName

- -

AssignmentElement [Yield] - : DestructuringAssignmentTarget Initializeropt

- -
    -
  1. Let v be Get(obj, propertyName).
    2. -
  2. ReturnIfAbrupt(v).
    3. -
  3. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue)
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    -
    4. -
  4. If DestructuringAssignmentTarget is an ObjectLiteral or an ArrayLiteral then -
      -
    1. Let AssignmentPattern be the parse of the source code corresponding to - DestructuringAssignmentTarget using either AssignmentPattern or - AssignmentPattern[Yield] as the goal symbol depending upon whether this - AssignmentElement has the Yield parameter.
      2. -
    2. If Type(v) is not Object, then throw a - TypeError exception.
      3. -
    3. Return the result of performing DestructuringAssignmentEvaluation of AssignmentPattern with v as - the argument.
      4. -
    -
    5. -
  5. Let lref be the result of evaluating DestructuringAssignmentTarget.
    6. -
  6. Return PutValue(lref,v).
    7. -
-
-
-
- -
-
-

12.15 Comma - Operator ( , )

-

Syntax

- -
-
Expression[In, Yield] :
-
AssignmentExpression[?In, ?Yield]
-
Expression[?In, ?Yield] , AssignmentExpression[?In, ?Yield]
-
-
- -
-

12.15.1 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 14.1.11, 14.4.8, 14.5.8.

- -
Expression : Expression , AssignmentExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.15.2 Static Semantics: IsValidSimpleAssignmentTarget

- -

See also: 12.2.0.3, 12.2.10.3, 12.3.1.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3.

- -
Expression : Expression , AssignmentExpression
-
    -
  1. Return false.
    2. -
-
- -
-

12.15.3 Runtime Semantics: Evaluation

-
Expression : Expression , AssignmentExpression
-
    -
  1. Let lref be the result of evaluating Expression.
    2. -
  2. ReturnIfAbrupt(GetValue(lref))
    3. -
  3. Let rref be the result of evaluating AssignmentExpression.
    4. -
  4. Return GetValue(rref).
    5. -
- -
-

NOTE GetValue must be called even though its value is not used - because it may have observable side-effects.

-
-
-
-
- -
-
-

13 ECMAScript Language: Statements and Declarations

-

Syntax

- -
-
Statement[Yield, Return] :
-
BlockStatement[?Yield, ?Return]
-
VariableStatement[?Yield]
-
EmptyStatement
-
ExpressionStatement[?Yield]
-
IfStatement[?Yield, ?Return]
-
BreakableStatement[?Yield, ?Return]
-
ContinueStatement[?Yield]
-
BreakStatement[?Yield]
-
[+Return] ReturnStatement[?Yield]
-
WithStatement[?Yield, ?Return]
-
LabelledStatement[?Yield, ?Return]
-
ThrowStatement[?Yield]
-
TryStatement[?Yield, ?Return]
-
DebuggerStatement
-
- -
-
Declaration[Yield, Default] :
-
FunctionDeclaration[?Yield,?Default]
-
GeneratorDeclaration[?Yield, ?Default]
-
ClassDeclaration[?Yield,?Default]
-
LexicalDeclaration[In, ?Yield]
-
- -
-
BreakableStatement[Yield, Return] :
-
IterationStatement[?Yield, ?Return]
-
SwitchStatement[?Yield, ?Return]
-
-
- -
-
-

13.0 - Statement Semantics

-
- -
-

13.0.1 Static Semantics: VarDeclaredNames

- -

See also: 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 0, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
-
Statement :
-
EmptyStatement
-
ExpressionStatement
-
ContinueStatement
-
BreakStatement
-
ReturnStatement
-
ThrowStatement
-
DebuggerStatement
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

13.0.2 Static Semantics: VarScopedDeclarations

- -

See also: 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
-
Statement :
-
EmptyStatement
-
ExpressionStatement
-
ContinueStatement
-
BreakStatement
-
ReturnStatement
-
ThrowStatement
-
DebuggerStatement
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

13.0.3 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.6, 13.12.4.

- -
BreakableStatement : IterationStatement
-
    -
  1. Let stmtResult be the result of performing LabelledEvaluation of IterationStatement with argument - labelSet.
    2. -
  2. If stmtResult.[[type]] is break and stmtResult.[[target]] - is empty, then -
      -
    1. If stmtResult.[[value]] is empty, then let stmtResult - be NormalCompletion(undefined).
      2. -
    2. Else, let stmtResult be NormalCompletion(stmtResult.[[value]])
      3. -
    -
    3. -
  3. Return stmtResult.
    4. -
-
BreakableStatement : SwitchStatement
-
    -
  1. Let stmtResult be the result of evaluating SwitchStatement.
    2. -
  2. If stmtResult.[[type]] is break and stmtResult.[[target]] - is empty, then -
      -
    1. If stmtResult.[[value]] is empty, then let stmtResult - be NormalCompletion(undefined).
      2. -
    2. Else, let stmtResult be NormalCompletion(stmtResult.[[value]])
      3. -
    -
    3. -
  3. Return stmtResult.
    4. -
- -
-

NOTE A BreakableStatement is one that can be exited via an unlabelled - BreakStatement.

-
-
- -
-

13.0.4 Runtime Semantics: Evaluation

- -
-
BreakableStatement :
-
IterationStatement
-
SwitchStatement
-
- -
    -
  1. Let newLabelSet be a new empty List.
    2. -
  2. Return the result of performing LabelledEvaluation of this BreakableStatement with argument - newLabelSet.
    3. -
-
-
- -
-
-

13.1 Block

-

Syntax

- -
-
BlockStatement[Yield, Return] :
-
Block[?Yield, ?Return]
-
- -
-
Block[Yield, Return] :
-
{ StatementList[?Yield, ?Return]opt }
-
- -
-
StatementList[Yield, Return] :
-
StatementListItem[?Yield, ?Return]
-
StatementList[?Yield, ?Return] StatementListItem[?Yield, ?Return]
-
- -
-
StatementListItem[Yield, Return] :
-
Statement[?Yield, ?Return]
-
Declaration[?Yield]
-
-
- -
-

13.1.1 Static Semantics: Early Errors

-
Block : { StatementList }
-
    -
  • -

    It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate - entries.

    -
    • - -
  • -

    It is a Syntax Error if any element of the LexicallyDeclaredNames of StatementList also - occurs in the VarDeclaredNames of StatementList.

    -
    • -
-
- -
-

13.1.2 Static Semantics: LexicallyScopedDeclarations

- -

See also: 13.11.2, 15.2.0.11.

- -
StatementList : StatementList StatementListItem
-
    -
  1. Let declarations be LexicallyScopedDeclarations of StatementList.
    2. -
  2. Append to declarations the elements of the LexicallyScopedDeclarations of StatementListItem.
    3. -
  3. Return declarations.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return a new empty List.
    2. -
-
StatementListItem : Declaration
-
    -
  1. Return a new List containing Declaration.
    2. -
-
- -
-

13.1.3 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.11.3, 14.1.14, 14.2.10, 14.4.8, 14.5.10, 15.1.3, 15.2.0.10.

- -
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let names be LexicallyDeclaredNames of StatementList.
    2. -
  2. Append to names the elements of the LexicallyDeclaredNames of StatementListItem.
    3. -
  3. Return names.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return a new empty List.
    2. -
-
StatementListItem : Declaration
-
    -
  1. Return the BoundNames of Declaration.
    2. -
-
- -
-

13.1.4 Static Semantics: TopLevelLexicallyDeclaredNames

-
StatementList : StatementList StatementListItem
-
    -
  1. Let names be TopLevelLexicallyDeclaredNames of StatementList.
    2. -
  2. Append to names the elements of the TopLevelLexicallyDeclaredNames of StatementListItem.
    3. -
  3. Return names.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return a new empty List.
    2. -
-
StatementListItem : Declaration
-
    -
  1. If Declaration is Declaration : FunctionDeclaration , then return a new empty List.
    2. -
  2. If Declaration is Declaration : GeneratorDeclaration , then return a new empty List.
    3. -
  3. Return the BoundNames of Declaration.
    4. -
- -
-

NOTE At the top level of a function, or script, function declarations are treated like var - declarations rather than like lexical declarations.

-
-
- -
-

13.1.5 Static Semantics: TopLevelLexicallyScopedDeclarations

-
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let declarations be TopLevelLexicallyScopedDeclarations of StatementList.
    2. -
  2. Append to declarations the elements of the TopLevelLexicallyScopedDeclarations of - StatementListItem.
    3. -
  3. Return declarations.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return a new empty List.
    2. -
-
StatementListItem : Declaration
-
    -
  1. If Declaration is Declaration : FunctionDeclaration , then return a new empty List.
    2. -
  2. If Declaration is Declaration : GeneratorDeclaration , then return a new empty List.
    3. -
  3. Return a new List containing Declaration.
    4. -
-
- -
-

13.1.6 Static Semantics: TopLevelVarDeclaredNames

-
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let names be TopLevelVarDeclaredNames of StatementList.
    2. -
  2. Append to names the elements of the TopLevelVarDeclaredNames of StatementListItem.
    3. -
  3. Return names.
    4. -
-
StatementListItem : Declaration
-
    -
  1. If Declaration is Declaration : FunctionDeclaration , then return the LexicallyDeclaredNames of Declaration.
    2. -
  2. If Declaration is Declaration : GeneratorDeclaration , then return the LexicallyDeclaredNames of Declaration.
    3. -
  3. Return a new empty List.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return VarDeclaredNames of Statement.
    2. -
- -
-

NOTE At the top level of a function or script, inner function declarations are treated like var - declarations.

-
-
- -
-

13.1.7 Static Semantics: TopLevelVarScopedDeclarations

-
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let declarations be TopLevelVarScopedDeclarations of StatementList.
    2. -
  2. Append to declarations the elements of the TopLevelVarScopedDeclarations of StatementListItem.
    3. -
  3. Return declarations.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return VarScopedDeclarations of Statement.
    2. -
-
StatementListItem : Declaration
-
    -
  1. If Declaration is Declaration : FunctionDeclaration , then return a new List containing FunctionDeclaration.
    2. -
  2. If Declaration is Declaration : GeneratorDeclaration , then return a new List containing GeneratorDeclaration.
    3. -
  3. Return a new empty List.
    4. -
-
- -
-

13.1.8 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 0, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let names be VarDeclaredNames of StatementList.
    2. -
  2. Append to names the elements of the VarDeclaredNames of StatementListItem.
    3. -
  3. Return names.
    4. -
-
StatementListItem : Declaration
-
    -
  1. Return a new empty List.
    2. -
-
- -
-

13.1.9 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
Block : { }
-
    -
  1. Return a new empty List.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let declarations be VarScopedDeclarations of StatementList.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of StatementListItem.
    3. -
  3. Return declarations.
    4. -
-
StatementListItem : Statement
-
    -
  1. Return VarScopedDeclarations of Statement.
    2. -
-
StatementListItem : Declaration
-
    -
  1. Return a new empty List.
    2. -
-
- -
-

13.1.10 Runtime Semantics: Evaluation

-
Block : { }
-
    -
  1. Return NormalCompletion(undefined).
    2. -
-
Block : { StatementList }
-
    -
  1. Let oldEnv be the running execution context’s LexicalEnvironment.
    2. -
  2. Let blockEnv be NewDeclarativeEnvironment(oldEnv).
    3. -
  3. Perform BlockDeclarationInstantiation(StatementList, - blockEnv).
    4. -
  4. Set the running execution context’s LexicalEnvironment to blockEnv.
    5. -
  5. Let blockValue be the result of evaluating StatementList.
    6. -
  6. Set the running execution context’s LexicalEnvironment to oldEnv.
    7. -
  7. If blockValue.[[type]] is normal and blockValue.[[value]] - is empty, then -
      -
    1. Return NormalCompletion(undefined).
      2. -
    -
    8. -
  8. Return blockValue.
    9. -
- -
-

NOTE No matter how control leaves the Block the LexicalEnvironment is always restored to its former state.

-
- -
StatementList : StatementList StatementListItem
-
    -
  1. Let sl be the result of evaluating StatementList.
    2. -
  2. ReturnIfAbrupt(sl).
    3. -
  3. Let s be the result of evaluating StatementListItem.
    4. -
  4. If s.[[type]] is throw, return s.
    5. -
  5. If s.[[value]] is empty, let V = sl.[[value]], - otherwise let V = s.[[value]].
    6. -
  6. Return Completion{[[type]]: s.[[type]], [[value]]: - V, [[target]]: s.[[target]]}.
    7. -
- -
-

NOTE Steps 5 and 6 of the above algorithm ensure that the value of a StatementList is - the value of the last value producing Statement in the StatementList. For example, the following calls to - the eval function all return the value 1:

- - 
eval("1;;;;;")
- 
eval("1;{}")
- 
eval("1;var a;")
-
-
- -
-

13.1.11 Runtime Semantics: BlockDeclarationInstantiation( code, env )

- -
-

NOTE When a Block or CaseBlock production is - evaluated a new Declarative Environment Record is created and bindings - for each block scoped variable, constant, or function declarated in the block are instantiated in the environment - record.

-
- -

BlockDeclarationInstantiation is performed as follows using arguments code and env. code - is the grammar production corresponding to the body of the block. env is the declarative environment record in which bindings are to be created.

- -
    -
  1. Let declarations be the LexicallyScopedDeclarations of code.
    2. -
  2. Let functionsToInitialize be an empty List.
    3. -
  3. For each element d in declarations do -
      -
    1. For each element dn of the BoundNames of d do -
        -
      1. If IsConstantDeclaration of d is true, then -
          -
        1. Call env’s CreateImmutableBinding concrete method passing dn as the argument.
          2. -
        -
        2. -
      2. Else, -
          -
        1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - dn and false as the arguments.
          2. -
        2. Assert: status is never an abrupt completion.
          3. -
        -
        3. -
      -
      2. -
    2. If d is a GeneratorDeclaration production or a FunctionDeclaration production, then -
        -
      1. Append d to functionsToInitialize.
        2. -
      -
      3. -
    -
    4. -
  4. For each production f in functionsToInitialize, in list order do -
      -
    1. Let fn be the sole element of the BoundNames of f.
      2. -
    2. Let fo be the result of performing InstantiateFunctionObject for f with argument env.
      3. -
    3. Call env’s InitializeBinding concrete method passing fn, and fo as the arguments.
      4. -
    -
    5. -
-
-
- -
-
-

13.2 Declarations and the Variable Statement

-
- -
-
-

13.2.1 Let and Const Declarations

- -
-

NOTE A let and const declarations define variables that are scoped - to the running execution context’s LexicalEnvironment. The variables are created when their containing Lexical Environment is instantiated but may not be accessed in any way until the - variable’s LexicalBinding is evaluated. A variable defined by a LexicalBinding with an Initializer is assigned the value of its Initializer’s AssignmentExpression when - the LexicalBinding is evaluated, not when the variable is created. If a LexicalBinding in a let declaration does not have an Initializer - the variable is assigned the value undefined when the LexicalBinding is evaluated.

-
- -

Syntax

- -
-
LexicalDeclaration[In, Yield] :
-
LetOrConst BindingList[?In, ?Yield] ;
-
- -
-
LetOrConst :
-
let
-
const
-
- -
-
BindingList[In, Yield] :
-
LexicalBinding[?In, ?Yield]
-
BindingList[?In, ?Yield] , LexicalBinding[?In, ?Yield]
-
- -
-
LexicalBinding[In, Yield] :
-
BindingIdentifier[?Yield] Initializer[?In, ?Yield]opt
-
BindingPattern[?Yield] Initializer[?In, ?Yield]
-
-
- -
-

13.2.1.1 Static Semantics: Early Errors

-
LexicalDeclaration : LetOrConst BindingList ;
-
    -
  • It is a Syntax Error if the BoundNames of BindingList contains "let".
    • -
  • It is a Syntax Error if the BoundNames of BindingList contains any duplicate entries.
    • -
-
LexicalBinding : BindingIdentifier Initializeropt
-
    -
  • -

    It is a Syntax Error if Initializer is not present and IsConstantDeclaration of the LexicalDeclaration containing this production is true.

    -
    • -
-
- -
-

13.2.1.2 Static Semantics: BoundNames

- -

See also:, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
LexicalDeclaration : LetOrConst BindingList ;
-
    -
  1. Return the BoundNames of BindingList.
    2. -
-
BindingList : BindingList , LexicalBinding
-
    -
  1. Let names be the BoundNames of BindingList.
    2. -
  2. Append to names the elements of the BoundNames of LexicalBinding.
    3. -
  3. Return names.
    4. -
-
LexicalBinding : BindingIdentifier Initializeropt
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
LexicalBinding : BindingPattern Initializer
-
    -
  1. Return the BoundNames of BindingPattern.
    2. -
-
- -
-

13.2.1.3 Static Semantics: IsConstantDeclaration

- -

See also: 14.1.8, 14.4.5, 14.5.5.

- -
LexicalDeclaration : LetOrConst BindingList ;
-
    -
  1. Return IsConstantDeclaration of LetOrConst.
    2. -
-
LetOrConst : let
-
    -
  1. Return false.
    2. -
-
LetOrConst : const
-
    -
  1. Return true.
    2. -
-
- -
-

13.2.1.4 Runtime Semantics: Evaluation

-
LexicalDeclaration : LetOrConst BindingList ;
-
    -
  1. Let next be the result of evaluating BindingList.
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. Return NormalCompletion(empty).
    4. -
-
BindingList : BindingList , LexicalBinding
-
    -
  1. Let next be the result of evaluating BindingList.
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. Return the result of evaluating LexicalBinding.
    4. -
-
LexicalBinding : BindingIdentifier
-
    -
  1. Let env be the running execution context’s LexicalEnvironment.
    2. -
  2. Return the result of performing BindingInitialization for BindingIdentifier passing undefined and - env as the arguments.
    3. -
- -
-

NOTE A static semantics rule ensures that this form of LexicalBinding - never occurs in a const declaration.

-
- -
LexicalBinding : BindingIdentifier Initializer
-
    -
  1. Let rhs be the result of evaluating Initializer.
    2. -
  2. Let value be GetValue(rhs).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. If IsAnonymousFunctionDefinition(Initializer) is - true, then -
      -
    1. Let hasNameProperty be HasOwnProperty(value, - "name").
      2. -
    2. ReturnIfAbrupt(hasNameProperty).
      3. -
    3. If hasNameProperty is false, then -
        -
      1. SetFunctionName(value, - StringValue(BindingIdentifier)).
        2. -
      -
      4. -
    -
    5. -
  5. Let env be the running execution context’s LexicalEnvironment.
    6. -
  6. Return the result of performing BindingInitialization for BindingIdentifier passing value and - env as the arguments.
    7. -
-
LexicalBinding : BindingPattern Initializer
-
    -
  1. Let rhs be the result of evaluating Initializer.
    2. -
  2. Let value be GetValue(rhs).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. If Type(value) is not Object, then throw a - TypeError exception.
    5. -
  5. Let env be the running execution context’s LexicalEnvironment.
    6. -
  6. Return the result of performing BindingInitialization for BindingPattern using value and env as - the arguments.
    7. -
-
-
- -
-
-

13.2.2 - Variable Statement

- -
-

NOTE A var statement declares variables that are scoped to the running execution context’s VariableEnvironment. Var variables are created when their containing Lexical Environment is instantiated and are initialized to undefined when - created. Within the scope of any VariableEnvironemnt a common Identifier may appear in more than - one VariableDeclaration but those declarations collective define only one variable. A variable - defined by a VariableDeclaration with an Initializer is assigned the - value of its Initializer’s AssignmentExpression when the VariableDeclaration is executed, not when the - variable is created.

-
- -

Syntax

- -
-
VariableStatement[Yield] :
-
var VariableDeclarationList[In, ?Yield] ;
-
- -
-
VariableDeclarationList[In, Yield] :
-
VariableDeclaration[?In, ?Yield]
-
VariableDeclarationList[?In, ?Yield] , VariableDeclaration[?In, ?Yield]
-
- -
-
VariableDeclaration[In, Yield] :
-
BindingIdentifier[?Yield] Initializer[?In, ?Yield]opt
-
BindingPattern[Yield] Initializer[?In, ?Yield]
-
-
- -
-

13.2.2.1 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
VariableDeclarationList : VariableDeclarationList , VariableDeclaration
-
    -
  1. Let names be BoundNames of VariableDeclarationList.
    2. -
  2. Append to names the elements of BoundNames of VariableDeclaration.
    3. -
  3. Return names.
    4. -
-
VariableDeclaration : BindingIdentifier Initializeropt
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
VariableDeclaration : BindingPattern Initializer
-
    -
  1. Return the BoundNames of BindingPattern.
    2. -
-
- -
-

13.2.2.2 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 0, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
VariableStatement : var VariableDeclarationList
-
    -
  1. Return BoundNames of VariableDeclarationList.
    2. -
-
- -
-

13.2.2.3 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
VariableDeclarationList : VariableDeclaration
-
    -
  1. Return a new List containing VariableDeclaration.
    2. -
-
VariableDeclarationList : VariableDeclarationList , VariableDeclaration
-
    -
  1. Let declarations be VarScopedDeclarations of VariableDeclarationList.
    2. -
  2. Append VariableDeclaration to declarations.
    3. -
  3. Return declarations.
    4. -
-
- -
-

13.2.2.4 Runtime Semantics: BindingInitialization

- -

With arguments value and environment.

- -

See also: 12.2.4.2.2, Error! Reference source not found., 13.2.3.4, 13.14.3.

- -
-

NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for - var statements formal parameter lists of non-strict functions. In those cases a lexical binding is hosted - and preinitialized prior to evaluation of its initializer.

-
- -
VariableDeclaration : BindingIdentifier
-
    -
  1. Return the result of performing BindingInitialization for BindingIdentifier passing value and - undefined as the arguments.
    2. -
-
VariableDeclaration : BindingIdentifier Initializer
-
    -
  1. Return the result of performing BindingInitialization for BindingIdentifier passing value and - undefined as the arguments.
    2. -
-
VariableDeclaration : BindingPattern Initializer
-
    -
  1. Return the result of performing BindingInitialization for BindingPattern passing value and - undefined as the arguments.
    2. -
-
- -
-

13.2.2.5 Runtime Semantics: - Evaluation

-
VariableStatement : var VariableDeclarationList ;
-
    -
  1. Let next be the result of evaluating VariableDeclarationList.
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. Return NormalCompletion( empty).
    4. -
-
VariableDeclarationList : VariableDeclarationList , VariableDeclaration
-
    -
  1. Let next be the result of evaluating VariableDeclarationList.
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. Return the result of evaluating VariableDeclaration.
    4. -
-
VariableDeclaration : BindingIdentifier
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
VariableDeclaration : BindingIdentifier Initializer
-
    -
  1. Let rhs be the result of evaluating Initializer.
    2. -
  2. Let value be GetValue(rhs).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. If IsAnonymousFunctionDefinition(Initializer) is - true, then -
      -
    1. Let hasNameProperty be HasOwnProperty(value, - "name").
      2. -
    2. ReturnIfAbrupt(hasNameProperty).
      3. -
    3. If hasNameProperty is false, then -
        -
      1. Perform SetFunctionName(value, - StringValue(BindingIdentifier)).
        2. -
      -
      4. -
    -
    5. -
  5. Return the result of performing BindingInitialization for BindingIdentifier passing value and - undefined as the arguments.
    6. -
- -
-

NOTE If a VariableDeclaration is nested within a with statement and the - Identifier in the VariableDeclaration is the same as a property name of the binding object of the with - statement’s object environment record, then step 3 will assign value - to the property instead of assigning to the VariableEnvironment binding of the - Identifier.

-
- -
VariableDeclaration : BindingPattern Initializer
-
    -
  1. Let rhs be the result of evaluating Initializer.
    2. -
  2. Let rval be GetValue(rhs).
    3. -
  3. ReturnIfAbrupt(rval).
    4. -
  4. If Type(rval) is not Object, then throw a - TypeError exception.
    5. -
  5. Return the result of performing BindingInitialization for BindingPattern passing rval and - undefined as arguments.
    6. -
-
-
- -
-
-

13.2.3 Destructuring Binding Patterns

-

Syntax

- -
-
BindingPattern[Yield,GeneratorParameter] :
-
ObjectBindingPattern[?Yield,?GeneratorParameter]
-
ArrayBindingPattern[?Yield,?GeneratorParameter]
-
- -
-
ObjectBindingPattern[Yield,GeneratorParameter] :
-
{ }
-
{ BindingPropertyList[?Yield,?GeneratorParameter] }
-
{ BindingPropertyList[?Yield,?GeneratorParameter] , }
-
- -
-
ArrayBindingPattern[Yield,GeneratorParameter] :
-
[ Elisionopt BindingRestElement[?Yield, ?GeneratorParameter]opt ]
-
[ BindingElementList[?Yield, ?GeneratorParameter] ]
-
[ BindingElementList[?Yield, ?GeneratorParameter] , Elisionopt BindingRestElement[?Yield, ?GeneratorParameter]opt ]
-
- -
-
BindingPropertyList[Yield,GeneratorParameter] :
-
BindingProperty[?Yield, ?GeneratorParameter]
-
BindingPropertyList[?Yield, ?GeneratorParameter] , BindingProperty[?Yield, ?GeneratorParameter]
-
- -
-
BindingElementList[Yield,GeneratorParameter] :
-
BindingElisionElement[?Yield, ?GeneratorParameter]
-
BindingElementList[?Yield, ?GeneratorParameter] , BindingElisionElement[?Yield, ?GeneratorParameter]
-
- -
-
BindingElisionElement[Yield,GeneratorParameter] :
-
Elisionopt BindingElement[?Yield, ?GeneratorParameter]
-
- -
-
BindingProperty[Yield,GeneratorParameter] :
-
SingleNameBinding[?Yield, ?GeneratorParameter]
-
PropertyName[?Yield, ?GeneratorParameter] : BindingElement[?Yield, ?GeneratorParameter]
-
- -
-
BindingElement[Yield,GeneratorParameter] :
-
SingleNameBinding[?Yield, ?GeneratorParameter]
-
[+GeneratorParameter] BindingPattern[?Yield,GeneratorParameter] Initializer[In]opt
-
[~GeneratorParameter] BindingPattern[?Yield] Initializer[In, ?Yield]opt
-
- -
-
SingleNameBinding[Yield,GeneratorParameter] :
-
[+GeneratorParameter] BindingIdentifier[Yield] Initializer[In]opt
-
[~GeneratorParameter] BindingIdentifier[?Yield] Initializer[In, ?Yield]opt
-
- -
-
BindingRestElement[Yield, GeneratorParameter] :
-
[+GeneratorParameter] ... BindingIdentifier[Yield]
-
[~GeneratorParameter] ... BindingIdentifier[?Yield]
-
-
- -
-

13.2.3.1 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
ObjectBindingPattern : { }
-
    -
  1. Return an empty List.
    2. -
-
ArrayBindingPattern : [ Elisionopt ]
-
    -
  1. Return an empty List.
    2. -
-
ArrayBindingPattern : [ Elisionopt BindingRestElement ]
-
    -
  1. Return the BoundNames of BindingRestElement.
    2. -
-
ArrayBindingPattern : [ BindingElementList , Elisionopt ]
-
    -
  1. Return the BoundNames of BindingElementList.
    2. -
-
ArrayBindingPattern : [ BindingElementList , Elisionopt BindingRestElement ]
-
    -
  1. Let names be BoundNames of BindingElementList.
    2. -
  2. Append to names the elements of BoundNames of BindingRestElement.
    3. -
  3. Return names.
    4. -
-
BindingPropertyList : BindingPropertyList , BindingProperty
-
    -
  1. Let names be BoundNames of BindingPropertyList.
    2. -
  2. Append to names the elements of BoundNames of BindingProperty.
    3. -
  3. Return names.
    4. -
-
BindingElementList : BindingElementList , BindingElisionElement
-
    -
  1. Let names be BoundNames of BindingElementList.
    2. -
  2. Append to names the elements of BoundNames of BindingElisionElement.
    3. -
  3. Return names.
    4. -
-
BindingElisionElement : Elisionopt BindingElement
-
    -
  1. Return BoundNames of BindingElement.
    2. -
-
BindingProperty : PropertyName : BindingElement
-
    -
  1. Return the BoundNames of BindingElement.
    2. -
-
SingleNameBinding : BindingIdentifier Initializeropt
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
BindingElement : BindingPattern Initializeropt
-
    -
  1. Return the BoundNames of BindingPattern.
    2. -
-
- -
-

13.2.3.2 Static Semantics: ContainsExpression

- -

See also: 14.1.5, 14.2.4.

- -
ObjectBindingPattern : { }
-
    -
  1. Return false.
    2. -
-
ArrayBindingPattern : [ Elisionopt ]
-
    -
  1. Return false.
    2. -
-
ArrayBindingPattern : [ Elisionopt BindingRestElement ]
-
    -
  1. Return false.
    2. -
-
ArrayBindingPattern : [ BindingElementList , Elisionopt ]
-
    -
  1. Return ContainsExpression of BindingElementList.
    2. -
-
ArrayBindingPattern : [ BindingElementList , Elisionopt BindingRestElement ]
-
    -
  1. Return ContainsExpression of BindingElementList.
    2. -
-
BindingPropertyList : BindingPropertyList , BindingProperty
-
    -
  1. Let has be ContainsExpression of BindingPropertyList.
    2. -
  2. If has is true, return true.
    3. -
  3. Return ContainsExpression of BindingProperty.
    4. -
-
BindingElementList : BindingElementList , BindingElisionElement
-
    -
  1. Let has be ContainsExpression of BindingElementList.
    2. -
  2. If has is true, return true.
    3. -
  3. Return ContainsExpression of BindingElisionElement.
    4. -
-
BindingElisionElement : Elisionopt BindingElement
-
    -
  1. Return ContainsExpression of BindingElement.
    2. -
-
BindingProperty : PropertyName : BindingElement
-
    -
  1. Let has be IsComputedPropertyKey of PropertyName.
    2. -
  2. If has is true, return true.
    3. -
  3. Return the ContainsExpression of BindingElement.
    4. -
-
BindingElement : BindingPattern Initializer
-
    -
  1. Return true.
    2. -
-
SingleNameBinding : BindingIdentifier
-
    -
  1. Return false.
    2. -
-
SingleNameBinding : BindingIdentifier Initializer
-
    -
  1. Return true.
    2. -
-
- -
-

13.2.3.3 Static Semantics: HasInitializer

- -

See also: 13.2.3.3, 14.1.7, 14.2.7.

- -
BindingElement : BindingPattern
-
    -
  1. Return false.
    2. -
-
BindingElement : BindingPattern Initializer
-
    -
  1. Return true.
    2. -
-
SingleNameBinding : BindingIdentifier
-
    -
  1. Return false.
    2. -
-
SingleNameBinding : BindingIdentifier Initializer
-
    -
  1. Return true.
    2. -
-
- -
-

13.2.3.4 Static Semantics: IsSimpleParameterList

- -

See also: 14.1.11, 14.2.8.

- -
BindingElement : BindingPattern
-
    -
  1. Return false.
    2. -
-
BindingElement : BindingPattern Initializer
-
    -
  1. Return false.
    2. -
-
SingleNameBinding : BindingIdentifier
-
    -
  1. Return true.
    2. -
-
SingleNameBinding : BindingIdentifier Initializer
-
    -
  1. Return false.
    2. -
-
- -
-

13.2.3.5 Runtime Semantics: BindingInitialization

- -

With parameters value and environment.

- -

See also: 12.2.4.2.2, Error! Reference source not found., 13.2.2.2, 13.14.3.

- -
-

NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for - formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order - to deal with the possibility of multiple parameters with the same name.

-
- -
BindingPattern : ObjectBindingPattern
-
    -
  1. Assert: Type(value) is Object
    2. -
  2. Return the result of performing BindingInitialization for ObjectBindingPattern using value and - environment as arguments.
    3. -
-
BindingPattern : ArrayBindingPattern
-
    -
  1. Assert: Type(value) is Object
    2. -
  2. Let iterator be GetIterator(value).
    3. -
  3. ReturnIfAbrupt(iterator).
    4. -
  4. Return the result of performing IteratorBindingInitialization for ArrayBindingPattern using iterator, - and environment as arguments.
    5. -
-
ObjectBindingPattern : { }
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
BindingPropertyList : BindingPropertyList , BindingProperty
-
    -
  1. Let status be the result of performing BindingInitialization for BindingPropertyList using - value and environment as arguments.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing BindingInitialization for BindingProperty using value and - environment as arguments.
    4. -
-
BindingProperty : SingleNameBinding
-
    -
  1. Let name be the string that is the only element of BoundNames of SingleNameBinding.
    2. -
  2. Return the result of performing KeyedBindingInitialization for SingleNameBinding using value, - environment, and name as the arguments.
    3. -
-
BindingProperty : PropertyName : BindingElement
-
    -
  1. Let P be the result of evaluating PropertyName
    2. -
  2. ReturnIfAbrupt(P).
    3. -
  3. Return the result of performing KeyedBindingInitialization for BindingElement using value, - environment, and P as arguments.
    4. -
-
- -
-

13.2.3.6 Runtime Semantics: IteratorBindingInitialization

- -

With parameters iterator, and environment.

- -

See also: 14.1.20, .

- -
-

NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for - formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order - to deal with the possibility of multiple parameters with the same name.

-
- -
ArrayBindingPattern : [ ]
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
ArrayBindingPattern : [ Elision ]
-
    -
  1. Return the result of performing IteratorDestructuringAssignmentEvaluation of Elision with iterator as - the argument.
    2. -
-
ArrayBindingPattern : [ Elisionopt BindingRestElement ]
-
    -
  1. If Elision is present, then -
      -
    1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    2. -
  2. Return the result of performing IteratorBindingInitialization for BindingRestElement using iterator - and environment as arguments.
    3. -
-
ArrayBindingPattern : [ BindingElementList ]
-
    -
  1. Return the result of performing IteratorBindingInitialization for BindingElementList using iterator - and environment as arguments.
    2. -
-
ArrayBindingPattern : [ BindingElementList , ]
-
    -
  1. Return the result of performing IteratorBindingInitialization for BindingElementList using iterator - and environment as arguments.
    2. -
-
ArrayBindingPattern : [ BindingElementList , Elision ]
-
    -
  1. Let status be the result of performing IteratorBindingInitialization for BindingElementList using - iterator and environment as arguments.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorDestructuringAssignmentEvaluation of Elision with iterator as - the argument.
    4. -
-
ArrayBindingPattern : [ BindingElementList , Elisionopt BindingRestElement ]
-
    -
  1. Let status be the result of performing IteratorBindingInitialization for BindingElementList using - iterator and environment as arguments.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. If Elision is present, then -
      -
    1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    4. -
  4. Return the result of performing IteratorBindingInitialization for BindingRestElement using iterator - and environment as arguments.
    5. -
-
BindingElementList : BindingElisionElement
-
    -
  1. Return the result of performing IteratorBindingInitialization for BindingElisionElement using - iterator and environment as arguments.
    2. -
-
BindingElementList : BindingElementList , BindingElisionElement
-
    -
  1. Let status be the result of performing IteratorBindingInitialization for BindingElementList iterator - and environment as arguments.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorBindingInitialization for BindingElisionElement using iterator - and environment as arguments.
    4. -
-
BindingElisionElement : BindingElement
-
    -
  1. Return the result of performing IteratorBindingInitialization of BindingElement with iterator and - environment as the arguments.
    2. -
-
BindingElisionElement : Elision BindingElement
-
    -
  1. Let status be the result of performing IteratorDestructuringAssignmentEvaluation of Elision with - iterator as the argument.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorBindingInitialization of BindingElement with iterator and - environment as the arguments.
    4. -
-
BindingElement : SingleNameBinding
-
    -
  1. Return the result of performing IteratorBindingInitialization for SingleNameBinding using iterator - and environment as the arguments.
    2. -
-
SingleNameBinding : BindingIdentifier Initializeropt
-
    -
  1. Let next be IteratorStep(iterator).
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. If next is false, then let v be undefined
    4. -
  4. Else -
      -
    1. Let v be IteratorValue(next).
      2. -
    2. ReturnIfAbrupt(v).
      3. -
    -
    5. -
  5. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue).
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    4. If IsAnonymousFunctionDefinition(Initializer) is - true, then -
        -
      1. Let hasNameProperty be HasOwnProperty(v, - "name").
        2. -
      2. ReturnIfAbrupt(hasNameProperty).
        3. -
      3. If hasNameProperty is false, then -
          -
        1. SetFunctionName(v, - StringValue(BindingIdentifier)).
          2. -
        -
        4. -
      -
      5. -
    -
    6. -
  6. Return the result of performing BindingInitialization for BindingIdentifier passing v and - environment as arguments.
    7. -
-
BindingElement : BindingPattern Initializeropt
-
    -
  1. Let next be IteratorStep(iterator).
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. If next is false, then let v be undefined
    4. -
  4. Else -
      -
    1. Let v be IteratorValue(next).
      2. -
    2. ReturnIfAbrupt(v).
      3. -
    -
    5. -
  5. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue)
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    -
    6. -
  6. If Type(v) is not Object, then throw a TypeError - exception.
    7. -
  7. Return the result of performing BindingInitialization of BindingPattern with v and environment - as the arguments.
    8. -
-
BindingRestElement : ... BindingIdentifier
-
    -
  1. Let A be ArrayCreate(0).
    2. -
  2. Let n=0.
    3. -
  3. Repeat, -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then -
        -
      1. Return the result of performing BindingInitialization for BindingIdentifier using A and - environment as arguments.
        2. -
      -
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let defineStatus be CreateDataPropertyOrThrow(A, ToString(ToUint32(n)), nextValue).
      7. -
    7. ReturnIfAbrupt(defineStatus).
      8. -
    8. Increment n by 1.
      9. -
    -
    4. -
-
- -
-

13.2.3.7 Runtime Semantics: KeyedBindingInitialization

- -

With parameters obj, environment, and propertyName.

- -
-

NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for - formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order - to deal with the possibility of multiple parameters with the same name.

-
- -
BindingElement : BindingPattern Initializeropt
-
    -
  1. Let v be Get(obj, propertyName).
    2. -
  2. ReturnIfAbrupt(v).
    3. -
  3. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue).
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    -
    4. -
  4. If Type(v) is not Object, then throw a TypeError - exception.
    5. -
  5. Return the result of performing BindingInitialization for BindingPattern passing v and - environment as arguments.
    6. -
-
SingleNameBinding : BindingIdentifier Initializeropt
-
    -
  1. Let v be Get(obj, propertyName).
    2. -
  2. ReturnIfAbrupt(v).
    3. -
  3. If Initializer is present and v is undefined, then -
      -
    1. Let defaultValue be the result of evaluating Initializer.
      2. -
    2. Let v be GetValue(defaultValue).
      3. -
    3. ReturnIfAbrupt(v).
      4. -
    4. If IsAnonymousFunctionDefinition(Initializer) is - true, then -
        -
      1. Let hasNameProperty be HasOwnProperty(v, - "name").
        2. -
      2. ReturnIfAbrupt(hasNameProperty).
        3. -
      3. If hasNameProperty is false, then -
          -
        1. SetFunctionName(v, - StringValue(BindingIdentifier)).
          2. -
        -
        4. -
      -
      5. -
    -
    4. -
  4. Return the result of performing BindingInitialization for BindingIdentifier passing v and - environment as arguments.
    5. -
-
-
-
- -
-
-

13.3 Empty - Statement

-

Syntax

- -
-
EmptyStatement :
-
;
-
-
- -
-

13.3.1 Runtime Semantics: Evaluation

-
EmptyStatement : ;
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
-
- -
-
-

13.4 - Expression Statement

-

Syntax

- -
-
ExpressionStatement[Yield] :
-
[lookahead ∉ {{, function, class, let [}] Expression[In, ?Yield] ;
-
- -
-

NOTE An ExpressionStatement cannot start with an opening curly brace because that might - make it ambiguous with a Block. Also, an ExpressionStatement cannot start with the function or - class keywords because that would make it ambiguous with a FunctionDeclaration, a - GeneratorDeclaration, or a ClassDeclaration. An ExpressionStatement cannot start with the two token - sequence let [ because that would make it ambiguous with a let LexicalDeclaration whose - first LexicalBinding was an ArrayBindingPattern.

-
-
- -
-

13.4.1 Runtime Semantics: Evaluation

-
ExpressionStatement : Expression ;
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let value be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. Return NormalCompletion(value).
    5. -
-
-
- -
-
-

13.5 The - if Statement

-

Syntax

- -
-
IfStatement[Yield, Return] :
-
if ( Expression[In, ?Yield] ) Statement[?Yield, ?Return] else Statement[?Yield, ?Return]
-
if ( Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
- -

Each else for which the choice of associated if is ambiguous shall be associated with the - nearest possible if that would otherwise have no corresponding else.

-
- -
-

13.5.1 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 0, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
IfStatement : if ( Expression ) Statement else Statement
-
    -
  1. Let names be VarDeclaredNames of the first Statement.
    2. -
  2. Append to names the elements of the VarDeclaredNames of the second Statement.
    3. -
  3. Return names.
    4. -
-
IfStatement : if ( Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.5.2 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
IfStatement : if ( Expression ) Statement else Statement
-
    -
  1. Let declarations be VarScopedDeclarations of the first Statement.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of the second Statement.
    3. -
  3. Return declarations.
    4. -
-
IfStatement : if ( Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.5.3 Runtime Semantics: Evaluation

-
IfStatement : if ( Expression ) Statement else Statement
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let exprValue be ToBoolean(GetValue(exprRef)).
    3. -
  3. ReturnIfAbrupt(exprValue).
    4. -
  4. If exprValue is true, then -
      -
    1. Let stmtValue be the result of evaluating the first Statement.
      2. -
    -
    5. -
  5. Else, -
      -
    1. Let stmtValue be the result of evaluating the second Statement.
      2. -
    -
    6. -
  6. If stmtValue.[[type]] is normal and stmtValue.[[value]] is - empty, then -
      -
    1. Return NormalCompletion(undefined).
      2. -
    -
    7. -
  7. Return stmtValue.
    8. -
-
IfStatement : if ( Expression ) Statement
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let exprValue be ToBoolean(GetValue(exprRef)).
    3. -
  3. ReturnIfAbrupt(exprValue).
    4. -
  4. If exprValue is false, then -
      -
    1. Return NormalCompletion(undefined).
      2. -
    -
    5. -
  5. Else, -
      -
    1. Let stmtValue be the result of evaluating Statement.
      2. -
    -
    6. -
  6. If stmtValue.[[type]] is normal and stmtValue.[[value]] is - empty, then -
      -
    1. Return NormalCompletion(undefined).
      2. -
    -
    7. -
  7. Return stmtValue.
    8. -
-
-
- -
-
-

13.6 - Iteration Statements

-

Syntax

- -
-
IterationStatement[Yield, Return] :
-
do Statement[?Yield, ?Return] while ( Expression[In, ?Yield] ) ;opt
-
while ( Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
for ( [lookahead ∉ {let [}] Expression[?Yield]opt ; Expression[In, ?Yield]opt ; Expression[In, ?Yield]opt ) Statement[?Yield, ?Return]
-
for ( var VariableDeclarationList[?Yield] ; Expression[In, ?Yield]opt ; Expression[In, ?Yield]opt ) Statement[?Yield, ?Return]
-
for ( LexicalDeclaration[?Yield] Expression[In, ?Yield]opt ; Expression[In, ?Yield]opt ) Statement[?Yield, ?Return]
-
for ( [lookahead ∉ {let [}] LeftHandSideExpression[?Yield] in Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
for ( var ForBinding[?Yield] in Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
for ( ForDeclaration[?Yield] in Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
for ( [lookahead ≠ let ] LeftHandSideExpression[?Yield] of AssignmentExpression[In, ?Yield] ) Statement [?Yield, ?Return]
-
for ( var ForBinding[?Yield] of AssignmentExpression[In, ?Yield] ) Statement[?Yield, ?Return]
-
for ( ForDeclaration[?Yield] of AssignmentExpression[In, ?Yield] ) Statement[?Yield, ?Return]
-
- -
-
ForDeclaration[Yield] :
-
LetOrConst ForBinding[?Yield]
-
- -
-

NOTE 1 ForBinding is defined in 12.2.4.2.

-
- -
-

NOTE 2 A semicolon is not required after a do-while statement.

-
-
- -
-
-

13.6.0 Semantics

-
- -
-

13.6.0.1 - Runtime Semantics: LoopContinues(completion, labelSet)

- -

The abstract operation LoopContinues with arguments - completion and labelSet is defined by the following step:

- -
    -
  1. If completion.[[type]] is normal, then return true.
    2. -
  2. If completion.[[type]] is not continue, then return - false.
    3. -
  3. If completion.[[target]] is empty, then return true.
    4. -
  4. If completion.[[target]] is an element of labelSet, then return true.
    5. -
  5. Return false.
    6. -
- -
-

NOTE Within the Statement part of an IterationStatement a - ContinueStatement may be used to begin a new iteration.

-
-
-
- -
-
-

13.6.1 - The do-while Statement

-
- -
-

13.6.1.1 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 0, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
IterationStatement : do Statement while ( Expression ) ;opt
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.6.1.2 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
IterationStatement : do Statement while ( Expression ) ;opt
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-

13.6.1.3 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.0.2, 13.6.2.2, 13.6.3.2, 13.6.4.6, 13.12.4.

- -
IterationStatement : do Statement while ( Expression ) ;opt
-
    -
  1. Let V = undefined.
    2. -
  2. Repeat -
      -
    1. Let stmt be the result of evaluating Statement.
      2. -
    2. If stmt.[[value]] is not empty, let V = - stmt.[[value]].
      3. -
    3. If LoopContinues (stmt,labelSet) is false, return - stmt.
      4. -
    4. Let exprRef be the result of evaluating Expression.
      5. -
    5. Let exprValue be ToBoolean(GetValue(exprRef)).
      6. -
    6. If exprValue is false, Return NormalCompletion(V).
      7. -
    7. Else if exprValue is not true, then -
        -
      1. Assert: exprValue is an abrupt completion.
        2. -
      2. If LoopContinues (exprValue,labelSet) is false, - return exprValue.
        3. -
      -
      8. -
    -
    3. -
-
-
- -
-
-

13.6.2 The - while Statement

-
- -
-

13.6.2.1 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.5.1, 13.6.1.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
IterationStatement : while ( Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.6.2.2 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 15.1.6, 15.2.0.14.

- -
IterationStatement : while ( Expression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-

13.6.2.3 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.0.2, 13.6.1.2, 13.6.3.2, 13.6.4.6, 13.12.4.

- -
IterationStatement : while ( Expression ) Statement
-
    -
  1. Let V = undefined.
    2. -
  2. Repeat -
      -
    1. Let exprRef be the result of evaluating Expression.
      2. -
    2. Let exprValue be ToBoolean(GetValue(exprRef)).
      3. -
    3. If exprValue is false, return NormalCompletion(V).
      4. -
    4. If exprValue is not true, then -
        -
      1. Assert: exprValue is an abrupt completion.
        2. -
      2. If LoopContinues (exprValue,labelSet) is false, - return exprValue.
        3. -
      -
      5. -
    5. Let stmt be the result of evaluating Statement.
      6. -
    6. If stmt.[[value]] is not empty, let V = - stmt.[[value]].
      7. -
    7. If LoopContinues (stmt,labelSet) is false, return - stmt.
      8. -
    -
    3. -
-
-
- -
-
-

13.6.3 The - for Statement

-
- -
-

13.6.3.1 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
IterationStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
IterationStatement : for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. Let names be BoundNames of VariableDeclarationList.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Statement.
    3. -
  3. Return names.
    4. -
-
IterationStatement : for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.6.3.2 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
IterationStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
IterationStatement : for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. Let declarations be VarScopedDeclarations of VariableDeclarationList.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Statement.
    3. -
  3. Return declarations.
    4. -
-
IterationStatement : for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-

13.6.3.3 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.0.2, 13.6.1.2, 13.6.2.2, 13.6.4.6, 13.12.4.

- -
IterationStatement : for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. If the first Expression is present, then -
      -
    1. Let exprRef be the result of evaluating the first Expression.
      2. -
    2. Let exprValue be GetValue(exprRef).
      3. -
    3. If LoopContinues(exprValue,labelSet) is false, return - exprValue.
      4. -
    -
    2. -
  2. Return the result of performing ForBodyEvaluation with the first Expression as the testExpr argument, - the second Expression as the incrementExpr argument, Statement as the stmt argument, () - as the perIterationBindings, and with labelSet.
    3. -
-
IterationStatement : for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement
-
    -
  1. Let varDcl be the result of evaluating VariableDeclarationList.
    2. -
  2. If LoopContinues(varDcl,labelSet) is false, return - varDcl.
    3. -
  3. Return the result of performing ForBodyEvaluation with the first Expression as the testExpr argument, - the second Expression as the incrementExpr argument, Statement as the stmt argument, () - as the perIterationBindings, and with labelSet.
    4. -
-
IterationStatement : for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
-
    -
  1. Let oldEnv be the running execution context’s LexicalEnvironment.
    2. -
  2. Let loopEnv be NewDeclarativeEnvironment(oldEnv).
    3. -
  3. Let isConst be the result of performing IsConstantDeclaration of LexicalDeclaration.
    4. -
  4. Let boundNames be the BoundNames of LexicalDeclaration.
    5. -
  5. For each element dn of boundNames do -
      -
    1. If isConst is true, then -
        -
      1. Call loopEnv’s CreateImmutableBinding concrete method passing dn as the argument.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Call loopEnv’s CreateMutableBinding concrete method passing dn and false as the - arguments.
        2. -
      2. Assert: The above call to CreateMutableBinding will never return an - abrupt completion.
        3. -
      -
      3. -
    -
    6. -
  6. Set the running execution context’s LexicalEnvironment to loopEnv.
    7. -
  7. Let forDcl be the result of evaluating LexicalDeclaration.
    8. -
  8. If LoopContinues(forDcl,labelSet) is false, then -
      -
    1. Set the running execution context’s LexicalEnvironment to oldEnv.
      2. -
    2. Return forDcl.
      3. -
    -
    9. -
  9. If isConst is false, let perIterationLets be boundNames otherwise let - perIterationLets be ( ).
    10. -
  10. Let bodyResult be the result of performing ForBodyEvaluation with the first Expression as the - testExpr argument, the second Expression as the incrementExpr argument, Statement as the - stmt argument, perIterationLets as the perIterationBindings, and with labelSet.
    11. -
  11. Set the running execution context’s LexicalEnvironment to oldEnv.
    12. -
  12. Return bodyResult.
    13. -
-
- -
-

13.6.3.4 Runtime Semantics: ForBodyEvaluation

- -

The abstract operation ForBodyEvaluation with arguments testExpr, incrementExpr, stmt, - perIterationBindings, and labelSet is performed as follows:

- -
    -
  1. Let V = undefined.
    2. -
  2. Let status be CreatePerIterationEnvironment(perIterationBindings).
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Repeat -
      -
    1. If testExpr is not [empty], then -
        -
      1. Let testExprRef be the result of evaluating testExpr.
        2. -
      2. Let testExprValue be ToBoolean(GetValue(testExprRef))
        3. -
      3. If testExprValue is false, return NormalCompletion(V).
        4. -
      4. Else if LoopContinues (testExprValue,labelSet) is - false, return testExprValue.
        5. -
      -
      2. -
    2. Let result be the result of evaluating stmt.
      3. -
    3. If result.[[value]] is not empty, let V = - result.[[value]].
      4. -
    4. If LoopContinues (result,labelSet) is false, return - result.
      5. -
    5. Let status be CreatePerIterationEnvironment(perIterationBindings).
      6. -
    6. ReturnIfAbrupt(status).
      7. -
    7. If incrementExpr is not [empty], then -
        -
      1. Let incExprRef be the result of evaluating incrementExpr.
        2. -
      2. Let incExprValue be GetValue(incExprRef).
        3. -
      3. If LoopContinues(incExprValue,labelSet) is false, - return incExprValue.
        4. -
      -
      8. -
    -
    5. -
-
- -
-

13.6.3.5 Runtime Semantics: CreatePerIterationEnvironment

- -

The abstract operation CreatePerIterationEnvironment with argument perIterationBindings is performed as - follows:

- -
    -
  1. If perIterationBindings has any elements, then -
      -
    1. Let lastIterationEnv be the running execution context’s LexicalEnvironment.
      2. -
    2. Let outer be lastIterationEnv’s outer environment - reference.
      3. -
    3. Assert: outer is not null.
      4. -
    4. Let thisIterationEnv be NewDeclarativeEnvironment(outer).
      5. -
    5. For each element bn of perIterationBindings do, -
        -
      1. Let status be the result of calling thisIterationEnv’s CreateMutableBinding concrete - method passing bn and false as the arguments.
        2. -
      2. Assert: status is never an abrupt completion.
        3. -
      3. Let lastValue be the result of calling lastIterationEnv’s GetBindingValue concrete - method passing bn and true as the arguments.
        4. -
      4. ReturnIfAbrupt(lastValue).
        5. -
      5. Call the InitializeBinding concrete method of thisIterationEnv passing bn and lastValue - as the arguments.
        6. -
      -
      6. -
    6. Set the running execution context’s LexicalEnvironment to thisIterationEnv.
      7. -
    -
    2. -
  2. Return undefined
    3. -
-
-
- -
-
-

13.6.4 The for-in and - for-of Statements

-
- -
-

13.6.4.1 Static Semantics: Early Errors

- -
-
IterationStatement :
-
for ( LeftHandSideExpression in Expression ) Statement
-
for ( LeftHandSideExpression of AssignmentExpression ) Statement
-
- -
    -
  • -

    It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched - by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.

    -
    • - -
  • -

    If LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression can be parsed with no tokens left over using AssignmentPattern as the goal symbol then the following rules are not applied. Instead, the Early - Error rules for AssignmentPattern are used.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is a IdentifierReference that can be statically determined to always resolve to a declarative environment record binding and the resolved binding is an - immutable binding.

    -
    • - -
  • -

    It is a Syntax Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.

    -
    • - -
  • -

    It is a Syntax Error if the LeftHandSideExpression is CoverParenthesizedExpressionAndArrowParameterList : - ( Expression ) and Expression derives a production that would produce a Syntax Error according to these rules if that - production is substituted for LeftHandSideExpression. This rule is recursively applied.

    -
    • -
- -
-

NOTE The last rule means that the other rules are applied even if parentheses surround - Expression.

-
- -
-
IterationStatement :
-
for ( ForDeclaration in Expression ) Statement
-
for ( ForDeclaration of AssignmentExpression ) Statement
-
- -
    -
  • -

    It is a Syntax Error if the BoundNames of ForDeclaration contains "let".

    -
    • - -
  • -

    It is a Syntax Error if any element of the BoundNames of ForDeclaration also occurs in the - VarDeclaredNames of Statement.

    -
    • -
-
- -
-

13.6.4.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
ForDeclaration : LetOrConst ForBinding
-
    -
  1. Return the BoundNames of ForBinding.
    2. -
-
- -
-

13.6.4.3 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
IterationStatement : for ( LeftHandSideExpression in Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
IterationStatement : for ( var ForBinding in Expression ) Statement
-
    -
  1. Let names be the BoundNames of ForBinding.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Statement.
    3. -
  3. Return names.
    4. -
-
IterationStatement : for ( ForDeclaration in Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
IterationStatement : for ( LeftHandSideExpression of AssignmentExpression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
IterationStatement : for ( var ForBinding of AssignmentExpression ) Statement
-
    -
  1. Let names be the BoundNames of ForBinding.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Statement.
    3. -
  3. Return names.
    4. -
-
IterationStatement : for ( ForDeclaration of AssignmentExpression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.6.4.4 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
IterationStatement : for ( LeftHandSideExpression in Expression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
IterationStatement : for ( var ForBinding in Expression ) Statement
-
    -
  1. Let declarations be a List containing - ForBinding.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Statement.
    3. -
  3. Return declarations.
    4. -
-
IterationStatement : for ( ForDeclaration in Expression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
IterationStatement : for ( LeftHandSideExpression of AssignmentExpression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
IterationStatement : for ( var ForBinding of AssignmentExpression ) Statement
-
    -
  1. Let declarations be a List containing - ForBinding.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Statement.
    3. -
  3. Return declarations.
    4. -
-
IterationStatement : for ( ForDeclaration of AssignmentExpression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-

13.6.4.5 Runtime Semantics: BindingInstantiation

- -

With arguments value and environment.

- -

See also: 13.0.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.12.4.

- -
ForDeclaration : LetOrConst ForBinding
-
    -
  1. For each element name of the BoundNames of ForBinding do -
      -
    1. If IsConstantDeclaration of LetOrConst is true, then -
        -
      1. Call environment’s CreateImmutableBinding concrete method with argument name.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Call environment’s CreateMutableBinding concrete method with argument name.
        2. -
      2. Assert: The above call to CreateMutableBinding will never return an - abrupt completion.
        3. -
      -
      3. -
    -
    2. -
  2. Return the result of performing BindingInitialization for ForBinding passing value and - environment as the arguments.
    3. -
-
- -
-

13.6.4.6 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.0.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.12.4.

- -
IterationStatement : for ( LeftHandSideExpression in Expression ) Statement
-
    -
  1. Let keyResult be ForIn/OfExpressionEvaluation( ( ), Expression, enumerate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with LeftHandSideExpression, Statement, - keyResult, assignment, and labelSet.
    4. -
-
IterationStatement : for ( var ForBinding in Expression ) Statement
-
    -
  1. Let keyResult be ForIn/OfExpressionEvaluation( ( ), Expression, enumerate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with ForBinding, Statement, keyResult, - varBinding, and labelSet.
    4. -
-
IterationStatement : for ( ForDeclaration in Expression ) Statement
-
    -
  1. Let keyResult be the result of performing ForIn/OfExpressionEvaluation(BoundNames of ForDeclaration, - Expression, enumerate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with ForDeclaration, Statement, - keyResult, lexicalBinding, and labelSet.
    4. -
-
IterationStatement : for ( LeftHandSideExpression of AssignmentExpression ) Statement
-
    -
  1. Let keyResult be the result of performing ForIn/OfExpressionEvaluation( ( ), AssignmentExpression, - iterate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with LeftHandSideExpression, Statement, - keyResult, assignment, and labelSet.
    4. -
-
IterationStatement : for ( var ForBinding of AssignmentExpression ) Statement
-
    -
  1. Let keyResult be the result of performing ForIn/OfExpressionEvaluation( ( ), AssignmentExpression, - iterate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with ForBinding, Statement, keyResult, - varBinding, and labelSet.
    4. -
-
IterationStatement : for ( ForDeclaration of AssignmentExpression ) Statement
-
    -
  1. Let keyResult be the result of performing ForIn/OfExpressionEvaluation( BoundNames of ForDeclaration, - AssignmentExpression, iterate, labelSet).
    2. -
  2. ReturnIfAbrupt(keyResult).
    3. -
  3. Return the result of performing ForIn/OfBodyEvaluation with ForDeclaration, Statement, - keyResult, lexicalBinding, and labelSet.
    4. -
-
- -
-

13.6.4.7 Runtime Semantics: ForIn/OfExpressionEvaluation Abstract - Operation

- -

The abstract operation ForIn/OfExpressionEvaluation is called with arguments TDZnames, - expr, iterationKind, and labelSet. The - value of iterationKind is either enumerate or iterate.

- -
    -
  1. Let oldEnv be the running execution context’s LexicalEnvironment.
    2. -
  2. If TDZnames is not an empty List, then -
      -
    1. Assert: TDZnames has no duplicate entries.
      2. -
    2. Let TDZ be NewDeclarativeEnvironment(oldEnv).
      3. -
    3. For each string name in TDZnames, do -
        -
      1. Let status be the result of calling TDZ’s CreateMutableBinding concrete method passing - name and false as the arguments.
        2. -
      2. Assert: status is never an abrupt completion.
        3. -
      -
      4. -
    4. Set the running execution context’s LexicalEnvironment to TDZ.
      5. -
    -
    3. -
  3. Let exprRef be the result of evaluating the production that is expr.
    4. -
  4. Set the running execution context’s LexicalEnvironment to oldEnv.
    5. -
  5. Let exprValue be GetValue(exprRef).
    6. -
  6. If exprValue is an abrupt completion, -
      -
    1. If LoopContinues(exprValue,labelSet) is false, then return - exprValue.
      2. -
    2. Else, return Completion{[[type]]: break, [[value]]: empty, - [[target]]: empty}.
      3. -
    -
    7. -
  7. If exprValue.[[value]] is null or undefined, then -
      -
    1. Return Completion{[[type]]: break, [[value]]: empty, [[target]]: empty}.
      2. -
    -
    8. -
  8. Let obj be ToObject(exprValue).
    9. -
  9. If iterationKind is enumerate, then -
      -
    1. Let keys be the result of calling the [[Enumerate]] internal method of obj with no arguments.
      2. -
    -
    10. -
  10. Else, -
      -
    1. Assert: iterationKind is iterate.
      2. -
    2. Let keys be GetIterator(obj).
      3. -
    -
    11. -
  11. If keys is an abrupt completion, then -
      -
    1. If LoopContinues(keys,labelSet) is false, then return - keys.
      2. -
    2. Assert: keys.[[type]] is continue
      3. -
    3. Return Completion{[[type]]: break, [[value]]: empty, [[target]]: empty}.
      4. -
    -
    12. -
  12. Return keys.
    13. -
-
- -
-

13.6.4.8 Runtime Semantics: ForIn/OfBodyEvaluation

- -

The abstract operation ForIn/OfBodyEvaluation is called with arguments lhs, stmt, keys, - lhsKind, and labelSet. The value of lhsKind is either assignment, - varBinding or lexicalBinding.

- -
    -
  1. Let oldEnv be the running execution context’s LexicalEnvironment.
    2. -
  2. Let V = undefined .
    3. -
  3. Repeat -
      -
    1. Let nextResult be IteratorStep(keys).
      2. -
    2. ReturnIfAbrupt(nextResult).
      3. -
    3. If nextResult is false, then return NormalCompletion(V).
      4. -
    4. Let nextValue be IteratorValue(nextResult).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. If lhsKind is assignment, then -
        -
      1. Assert: lhs is a LeftHandSideExpression.
        2. -
      2. If lhs is neither an ObjectLiteral nor an ArrayLiteral then -
          -
        1. Let lhsRef be the result of evaluating lhs ( it may be evaluated repeatedly).
          2. -
        2. Let status be PutValue(lhsRef, nextValue).
          3. -
        -
        3. -
      3. Else -
          -
        1. Let assignmentPattern be the parse of the source code corresponding to lhs using - AssignmentPattern as the goal symbol.
          2. -
        2. If Type(nextValue) is not Object, then throw - a TypeError exception.
          3. -
        3. Let status be the result of performing DestructuringAssignmentEvaluation of - AssignmentPattern using nextValue as the argument.
          4. -
        -
        4. -
      -
      7. -
    7. Else if lhsKind is varBinding, then -
        -
      1. Assert: lhs is a ForBinding.
        2. -
      2. Let status be the result of performing BindingInitialization for lhs passing nextValue - and undefined as the arguments.
        3. -
      -
      8. -
    8. Else, -
        -
      1. Assert: lhsKind is lexicalBinding.
        2. -
      2. Assert: lhs is a ForDeclaration.
        3. -
      3. Let iterationEnv be NewDeclarativeEnvironment(oldEnv).
        4. -
      4. Let status be the result of performing BindingInstantiation for lhs passing nextValue - and iterationEnv as arguments.
        5. -
      5. Assert: status is not an abrupt completion.
        6. -
      6. Set the running execution context’s LexicalEnvironment to iterationEnv.
        7. -
      -
      9. -
    9. If status.[[type]] is normal, then -
        -
      1. Let status be the result of evaluating stmt.
        2. -
      2. If status.[[type]] is normal and status.[[value]] - is not empty, then -
          -
        1. Let V = status.[[value]].
          2. -
        -
        3. -
      -
      10. -
    10. Set the running execution context’s LexicalEnvironment to oldEnv.
      11. -
    11. If status is an abrupt completion and LoopContinues(status,labelSet) is false, then return - status.
      12. -
    -
    4. -
-
-
-
- -
-
-

13.7 The - continue Statement

-

Syntax

- -
-
ContinueStatement[Yield] :
-
continue ;
-
continue [no LineTerminator here] LabelIdentifier[?Yield] ;
-
-
- -
-

13.7.1 Static Semantics: Early Errors

-
ContinueStatement : continue ;
-
    -
  • -

    It is a Syntax Error if this production is not nested, directly or indirectly (but not crossing function boundaries), - within an IterationStatement.

    -
    • -
-
ContinueStatement : continue LabelIdentifier ;
-
    -
  • -

    It is a Syntax Error if this production is not nested, directly or indirectly (but not crossing function boundaries), - within an IterationStatement.

    -
    • - -
  • -

    It is a Syntax Error if StringValue(LabelIdentifier) does not appear in the enclosing - IterationLabelSet of this ContinueStatement.

    -
    • -
-
- -
-

13.7.2 Runtime Semantics: Evaluation

-
ContinueStatement : continue ;
-
    -
  1. Return Completion{[[type]]: continue, [[value]]: empty, [[target]]: empty}.
    2. -
-
ContinueStatement : continue LabelIdentifier ;
-
    -
  1. Let label be the StringValue of LabelIdentifier.
    2. -
  2. Return Completion{[[type]]: continue, [[value]]: empty, [[target]]: label - }.
    3. -
-
-
- -
-
-

13.8 The - break Statement

-

Syntax

- -
-
BreakStatement[Yield] :
-
break ;
-
break [no LineTerminator here] LabelIdentifier[?Yield] ;
-
-
- -
-

13.8.1 Static Semantics: Early Errors

-
BreakStatement : break ;
-
    -
  • -

    It is a Syntax Error if this production is not nested, directly or indirectly (but not crossing function boundaries), - within an IterationStatement or a SwitchStatement.

    -
    • -
-
BreakStatement : break LabelIdentifier ;
-
    -
  • -

    It is a Syntax Error if StringValue(LabelIdentifier) does not appear in the enclosing - CurrentLabelSet of this BreakStatement.

    -
    • -
-
- -
-

13.8.2 Runtime Semantics: Evaluation

-
BreakStatement : break ;
-
    -
  1. Return Completion{[[type]]: break, [[value]]: empty, [[target]]: empty}.
    2. -
-
BreakStatement : break LabelIdentifier ;
-
    -
  1. Let label be the StringValue of LabelIdentifier.
    2. -
  2. Return Completion{[[type]]: break, [[value]]: empty, [[target]]: label - }.
    3. -
-
-
- -
-
-

13.9 The - return Statement

-

Syntax

- -
-
ReturnStatement[Yield] :
-
return ;
-
return [no LineTerminator here] Expression[In, ?Yield] ;
-
- -
-

NOTE A return statement causes a function to cease execution and return a value to - the caller. If Expression is omitted, the return value is undefined. Otherwise, the return - value is the value of Expression.

-
-
- -
-

13.9.1 Runtime Semantics: Evaluation

-
ReturnStatement : return ;
-
    -
  1. Return Completion{[[type]]: return, [[value]]: undefined, [[target]]: empty}.
    2. -
-
ReturnStatement : return Expression ;
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let exprValue be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(exprValue).
    4. -
  4. Return Completion{[[type]]: return, [[value]]: exprValue, [[target]]: empty}.
    5. -
-
-
- -
-
-

13.10 The - with Statement

-

Syntax

- -
-
WithStatement[Yield, Return] :
-
with ( Expression[In, ?Yield] ) Statement[?Yield, ?Return]
-
- -
-

NOTE The with statement adds an object - environment record for a computed object to the lexical environment of the running execution context. It then executes a statement using this augmented lexical environment. Finally, it restores the original lexical environment.

-
-
- -
-

13.10.1 Static Semantics: Early Errors

-
WithStatement : with ( Expression ) Statement
-
    -
  • -

    It is a Syntax Error if the code that matches this production is contained in strict - code.

    -
    • -
-
- -
-

13.10.2 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
WithStatement : with ( Expression ) Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.10.3 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
WithStatement : with ( Expression ) Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-

13.10.4 Runtime Semantics: Evaluation

-
WithStatement : with ( Expression ) Statement
-
    -
  1. Let val be the result of evaluating Expression.
    2. -
  2. Let obj be ToObject(GetValue(val)).
    3. -
  3. ReturnIfAbrupt(obj).
    4. -
  4. Let oldEnv be the running execution context’s LexicalEnvironment.
    5. -
  5. Let newEnv be NewObjectEnvironment(obj, oldEnv).
    6. -
  6. Set the withEnvironment flag of newEnv’s environment record to true.
    7. -
  7. Set the running execution context’s LexicalEnvironment to newEnv.
    8. -
  8. Let C be the result of evaluating Statement.
    9. -
  9. Set the running execution context’s Lexical Environment to oldEnv.
    10. -
  10. Return C.
    11. -
- -
-

NOTE No matter how control leaves the embedded Statement, whether normally or by some - form of abrupt completion or exception, the LexicalEnvironment is always restored to its former state.

-
-
-
- -
-
-

13.11 The - switch Statement

-

Syntax

- -
-
SwitchStatement[Yield, Return] :
-
switch ( Expression[In, ?Yield] ) CaseBlock[?Yield, ?Return]
-
- -
-
CaseBlock[Yield, Return] :
-
{ CaseClauses[?Yield, ?Return]opt }
-
{ CaseClauses[?Yield, ?Return]opt DefaultClause[?Yield, ?Return] CaseClauses[?Yield, ?Return]opt }
-
- -
-
CaseClauses[Yield, Return] :
-
CaseClause[?Yield, ?Return]
-
CaseClauses[?Yield, ?Return] CaseClause[?Yield, ?Return]
-
- -
-
CaseClause[Yield, Return] :
-
case Expression[In, ?Yield] : StatementList[?Yield, ?Return]opt
-
- -
-
DefaultClause[Yield, Return] :
-
default : StatementList[?Yield, ?Return]opt
-
-
- -
-

13.11.1 Static Semantics: Early Errors

-
CaseBlock : { CaseClauses }
-
    -
  • -

    It is a Syntax Error if the LexicallyDeclaredNames of CaseClauses contains any duplicate - entries.

    -
    • - -
  • -

    It is a Syntax Error if any element of the LexicallyDeclaredNames of CaseClauses also occurs - in the VarDeclaredNames of CaseClauses.

    -
    • -
-
- -
-

13.11.2 Static Semantics: LexicallyScopedDeclarations

- -

See also: 13.1.2, 15.2.0.11.

- -
CaseBlock : { }
-
    -
  1. Return a new empty List.
    2. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. If the first CaseClauses is present, let declarations be the LexicallyScopedDeclarations of the first - CaseClauses.
    2. -
  2. Else let declarations be a new empty List.
    3. -
  3. Append to declarations the elements of the LexicallyScopedDeclarations of the DefaultClause.
    4. -
  4. If the second CaseClauses is not present, return declarations.
    5. -
  5. Else return the result of appending to declarations the elements of the LexicallyScopedDeclarations of the - second CaseClauses.
    6. -
-
CaseClauses : CaseClauses CaseClause
-
    -
  1. Let declarations be LexicallyScopedDeclarations of CaseClauses.
    2. -
  2. Append to declarations the elements of the LexicallyScopedDeclarations of CaseClause.
    3. -
  3. Return declarations.
    4. -
-
CaseClause : case Expression : StatementListopt
-
    -
  1. If the StatementList is present, return the LexicallyScopedDeclarations of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
DefaultClause : default : StatementListopt
-
    -
  1. If the StatementList is present, return the LexicallyScopedDeclarations of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
- -
-

13.11.3 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 14.1.14, 14.2.10, 14.4.8, 14.5.10, 15.1.3, 15.2.0.10.

- -
CaseBlock : { }
-
    -
  1. Return a new empty List.
    2. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. If the first CaseClauses is present, let names be the LexicallyDeclaredNames of the first - CaseClauses.
    2. -
  2. Else let names be a new empty List.
    3. -
  3. Append to names the elements of the LexicallyDeclaredNames of the DefaultClause.
    4. -
  4. If the second CaseClauses is not present, return names.
    5. -
  5. Else return the result of appending to names the elements of the LexicallyDeclaredNames of the second - CaseClauses.
    6. -
-
CaseClauses : CaseClauses CaseClause
-
    -
  1. Let names be LexicallyDeclaredNames of CaseClauses.
    2. -
  2. Append to names the elements of the LexicallyDeclaredNames of CaseClause.
    3. -
  3. Return names.
    4. -
-
CaseClause : case Expression : StatementListopt
-
    -
  1. If the StatementList is present, return the LexicallyDeclaredNames of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
DefaultClause : default : StatementListopt
-
    -
  1. If the StatementList is present, return the LexicallyDeclaredNames of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
- -
-

13.11.4 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
SwitchStatement : switch ( Expression ) CaseBlock
-
    -
  1. Return the VarDeclaredNames of CaseBlock.
    2. -
-
CaseBlock : { }
-
    -
  1. Return a new empty List.
    2. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. If the first CaseClauses is present, let names be the VarDeclaredNames of the first - CaseClauses.
    2. -
  2. Else let names be a new empty List.
    3. -
  3. Append to names the elements of the VarDeclaredNames of the DefaultClause.
    4. -
  4. If the second CaseClauses is not present, return names.
    5. -
  5. Else return the result of appending to names the elements of the VarDeclaredNames of the second - CaseClauses.
    6. -
-
CaseClauses : CaseClauses CaseClause
-
    -
  1. Let names be VarDeclaredNames of CaseClauses.
    2. -
  2. Append to names the elements of the VarDeclaredNames of CaseClause.
    3. -
  3. Return names.
    4. -
-
CaseClause : case Expression : StatementListopt
-
    -
  1. If the StatementList is present, return the VarDeclaredNames of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
DefaultClause : default : StatementListopt
-
    -
  1. If the StatementList is present, return the VarDeclaredNames of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
- -
-

13.11.5 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
SwitchStatement : switch ( Expression ) CaseBlock
-
    -
  1. Return the VarScopedDeclarations of CaseBlock.
    2. -
-
CaseBlock : { }
-
    -
  1. Return a new empty List.
    2. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. If the first CaseClauses is present, let declarations be the VarScopedDeclarations of the first - CaseClauses.
    2. -
  2. Else let declarations be a new empty List.
    3. -
  3. Append to declarations the elements of the VarScopedDeclarations of the DefaultClause.
    4. -
  4. If the second CaseClauses is not present, return declarations.
    5. -
  5. Else return the result of appending to declarations the elements of the VarScopedDeclarations of the second - CaseClauses.
    6. -
-
CaseClauses : CaseClauses CaseClause
-
    -
  1. Let declarations be VarScopedDeclarations of CaseClauses.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of CaseClause.
    3. -
  3. Return declarations.
    4. -
-
CaseClause : case Expression : StatementListopt
-
    -
  1. If the StatementList is present, return the VarScopedDeclarations of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
DefaultClause : default : StatementListopt
-
    -
  1. If the StatementList is present, return the VarScopedDeclarations of StatementList.
    2. -
  2. Else return a new empty List.
    3. -
-
- -
-

13.11.6 Runtime Semantics: CaseBlockEvaluation

- -

With argument input.

- -
CaseBlock : { CaseClausesopt }
-
    -
  1. Let V = undefined.
    2. -
  2. Let A be the list of CaseClause items in source text order.
    3. -
  3. Let searching be true.
    4. -
  4. Repeat, for each CaseClause, C, in A -
      -
    1. If searching is true, then -
        -
      1. Let clauseSelector be the result of CaseSelectorEvaluation of C.
        2. -
      2. ReturnIfAbrupt(clauseSelector).
        3. -
      3. Let matched be the result of performing Strict Equality Comparison input === - clauseSelector.
        4. -
      4. If matched is true, then -
          -
        1. Set searching to false.
          2. -
        2. If C has a StatementList, then -
            -
          1. Let V be the result of evaluating C’s StatementList.
            2. -
          2. ReturnIfAbrupt(V).
            3. -
          -
          3. -
        -
        5. -
      -
      2. -
    2. Else searching is false, -
        -
      1. If C has a StatementList, then -
          -
        1. Let R be the result of evaluating C’s StatementList.
          2. -
        2. If R.[[value]] is not empty, then let V = - R.[[value]].
          3. -
        3. If R is an abrupt completion, then return - Completion{[[type]]: R.[[type]], [[value]]: - V, [[target]]: R.[[target]]}.
          4. -
        -
        2. -
      -
      3. -
    -
    5. -
  5. Return NormalCompletion(V).
    6. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. Let V = undefined.
    2. -
  2. Let A be the list of CaseClause items in the first CaseClauses, in source text order.
    3. -
  3. Let found be false.
    4. -
  4. Repeat letting C be in order each CaseClause in A -
      -
    1. If found is false, then -
        -
      1. Let clauseSelector be the result of CaseSelectorEvaluation of C.
        2. -
      2. If clauseSelector is an abrupt completion, then -
          -
        1. If clauseSelector.[[value]] is empty, then return Completion{[[type]]: clauseSelector.[[type]], - [[value]]: undefined, [[target]]: clauseSelector.[[target]]}.
          2. -
        2. Else, return clauseSelector.
          3. -
        -
        3. -
      3. Let found be the result of performing Strict Equality Comparison input === - clauseSelector.
        4. -
      -
      2. -
    2. If found is true, then -
        -
      1. Let R be the result of evaluating CaseClause C.
        2. -
      2. If R.[[value]] is not empty, then let V = - R.[[value]].
        3. -
      3. If R is an abrupt completion, then return Completion{[[type]]: R.[[type]], [[value]]: - V, [[target]]: R.[[target]]}.
        4. -
      -
      3. -
    -
    5. -
  5. Let foundInB be false.
    6. -
  6. If found is false, then -
      -
    1. Let B be a new List containing the CaseClause - items in the second CaseClauses, in source text order.
      2. -
    2. Repeat, letting C be in order each CaseClause in B -
        -
      1. If foundInB is false, then -
          -
        1. Let clauseSelector be the result of CaseSelectorEvaluation of C.
          2. -
        2. If clauseSelector is an abrupt completion, - then -
            -
          1. If clauseSelector.[[value]] is empty, then return - Completion{[[type]]: - clauseSelector.[[type]], [[value]]: undefined, [[target]]: - clauseSelector.[[target]]}.
            2. -
          2. Else, return clauseSelector.
            3. -
          -
          3. -
        3. Let foundInB be the result of performing Strict Equality Comparison input === - clauseSelector.
          4. -
        -
        2. -
      2. If foundInB is true, then -
          -
        1. Let R be the result of evaluating CaseClause C.
          2. -
        2. If R.[[value]] is not empty, then let V = - R.[[value]].
          3. -
        3. If R is an abrupt completion, then return - Completion{[[type]]: R.[[type]], [[value]]: - V, [[target]]: R.[[target]]}.
          4. -
        -
        3. -
      -
      3. -
    -
    7. -
  7. If foundInB is true, then return NormalCompletion(V).
    8. -
  8. Let R be the result of evaluating DefaultClause.
    9. -
  9. If R.[[value]] is not empty, then let V = - R.[[value]].
    10. -
  10. If R is an abrupt completion, then return Completion{[[type]]: R.[[type]], [[value]]: V, - [[target]]: R.[[target]]}.
    11. -
  11. Let B be a new List containing the CaseClause - items in the second CaseClauses, in source text order.
    12. -
  12. Repeat, letting C be in order each CaseClause in B (NOTE this is another complete iteration of - the second CaseClauses) -
      -
    1. Let R be the result of evaluating CaseClause C.
      2. -
    2. If R.[[value]] is not empty, then let V = - R.[[value]].
      3. -
    3. If R is an abrupt completion, then return Completion{[[type]]: R.[[type]], [[value]]: V, - [[target]]: R.[[target]]}.
      4. -
    -
    13. -
  13. Return NormalCompletion(V).
    14. -
-
- -
-

13.11.7 Runtime Semantics: CaseSelectorEvaluation

-
CaseClause : case Expression : StatementListopt
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Return GetValue(exprRef).
    3. -
- -
-

NOTE CaseSelectorEvaluation does not execute the associated StatementList. It simply - evaluates the Expression and returns the value, which the CaseBlock algorithm uses to determine which - StatementList to start executing.

-
-
- -
-

13.11.8 Runtime Semantics: Evaluation

-
SwitchStatement : switch ( Expression ) CaseBlock
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let switchValue be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(switchValue).
    4. -
  4. Let oldEnv be the running execution context’s LexicalEnvironment.
    5. -
  5. Let blockEnv be NewDeclarativeEnvironment(oldEnv).
    6. -
  6. Perform BlockDeclarationInstantiation(CaseBlock, - blockEnv).
    7. -
  7. Let R be the result of performing CaseBlockEvaluation of CaseBlock with argument - switchValue.
    8. -
  8. Set the running execution context’s LexicalEnvironment to oldEnv.
    9. -
  9. Return R.
    10. -
- -
-

NOTE No matter how control leaves the SwitchStatement the LexicalEnvironment is always restored to its former state.

-
- -
CaseClause : case Expression :
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
CaseClause : case Expression : StatementList
-
    -
  1. Return the result of evaluating StatementList.
    2. -
-
DefaultClause : default :
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
DefaultClause : default : StatementList
-
    -
  1. Return the result of evaluating StatementList.
    2. -
-
-
- -
-
-

13.12 - Labelled Statements

-

Syntax

- -
-
LabelledStatement[Yield, Return] :
-
LabelIdentifier[?Yield] : Statement[?Yield, ?Return]
-
- -
-

NOTE A Statement may be prefixed by a label. Labelled statements are - only used in conjunction with labelled break and continue statements. ECMAScript has no - goto statement. A Statement can be part of a LabelledStatement, which itself can be part of a LabelledStatement, and so on. - The labels introduced this way are collectively referred to as the “current label set” when describing the - semantics of individual statements. A LabelledStatement has no semantic meaning other than the - introduction of a label to a label set.

-
-
- -
-

13.12.1 Static Semantics: Early Errors

-
LabelledStatement : LabelIdentifier : Statement
-
    -
  • -

    It is a Syntax Error if the immediately enclosing CurrentLabelSet contains the StringValue of LabelIdentifier.

    -
    • -
-
- -
-

13.12.2 Static Semantics: CurrentLabelSet

-
LabelledStatement : LabelIdentifier : Statement
-
    -
  1. The CurrentLabelSet of this LabelledStatement is a List - that includes the StringValue of LabelIdentifier and all elements of the immediately enclosing - CurrentLabelSet.
    2. -
-
- -
-

13.12.3 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
LabelledStatement : LabelIdentifier : Statement
-
    -
  1. Return the VarDeclaredNames of Statement.
    2. -
-
- -
-

13.12.4 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
LabelledStatement : LabelIdentifier : Statement
-
    -
  1. Return the VarScopedDeclarations of Statement.
    2. -
-
- -
-
-

13.12.5 Runtime Semantics: LabelledEvaluation

- -

With argument labelSet.

- -

See also: 13.0.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.6.

- -
LabelledStatement : LabelIdentifier : Statement
-
    -
  1. Let label be the StringValue of LabelIdentifier.
    2. -
  2. Return LabelledStatementEvaluation(label, Statement, - labelSet).
    3. -
-
- -
-

13.12.5.1 Runtime Semantics: LabelledStatementEvaluation(label, stmt, - labelSet)

- -

The abstract operation LabelledStatementEvaluation with arguments label, stmt, and - labelSet is performed as follows:

- -
    -
  1. Let newLabelSet be a new List containing label - and the elements of labelSet.
    2. -
  2. If stmt is either a LabelledStatement or a BreakableStatement, then -
      -
    1. Let stmtResult be the result of performing LabelledEvaluation of stmt with argument - newLabelSet.
      2. -
    -
    3. -
  3. Else, -
      -
    1. Let stmtResult be the result of evaluating stmt.
      2. -
    -
    4. -
  4. If stmtResult.[[type]] is break and SameValue(stmtResult.[[target]], label), then -
      -
    1. Let result be NormalCompletion(stmtResult.[[value]]).
      2. -
    -
    5. -
  5. Else, -
      -
    1. Let result be stmtResult.
      2. -
    -
    6. -
  6. Return result.
    7. -
-
- -
-

13.12.5.2 Runtime Semantics: Evaluation

-
LabelledStatement : LabelIdentifier : Statement
-
    -
  1. Let newLabelSet be a new empty List.
    2. -
  2. Return the result of performing LabelledEvaluation of this LabelledStatement with argument - newLabelSet.
    3. -
-
-
-
- -
-
-

13.13 The - throw Statement

-

Syntax

- -
-
ThrowStatement[Yield] :
-
throw [no LineTerminator here] Expression[In, ?Yield] ;
-
-
- -
-

13.13.1 Runtime Semantics: Evaluation

-
ThrowStatement : throw Expression ;
-
    -
  1. Let exprRef be the result of evaluating Expression.
    2. -
  2. Let exprValue be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(exprValue).
    4. -
  4. Return Completion{[[type]]: throw, [[value]]: exprValue, [[target]]: empty}.
    5. -
-
-
- -
-
-

13.14 The - try Statement

-

Syntax

- -
-
TryStatement[Yield, Return] :
-
try Block[?Yield, ?Return] Catch[?Yield, ?Return]
-
try Block[?Yield, ?Return] Finally[?Yield, ?Return]
-
try Block[?Yield, ?Return] Catch[?Yield, ?Return] Finally[?Yield, ?Return]
-
- -
-
Catch[Yield, Return] :
-
catch ( CatchParameter[?Yield] ) Block[?Yield, ?Return]
-
- -
-
Finally[Yield, Return] :
-
finally Block[?Yield, ?Return]
-
- -
-
CatchParameter[Yield] :
-
BindingIdentifier[?Yield]
-
BindingPattern[?Yield]
-
- -
-

NOTE The try statement encloses a block of code in which an exceptional condition - can occur, such as a runtime error or a throw statement. The catch clause provides the - exception-handling code. When a catch clause catches an exception, its CatchParameter is bound to that - exception.

-
-
- -
-

13.14.1 Static Semantics: Early Errors

-
Catch : catch ( CatchParameter ) Block
-
    -
  • -

    It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the - LexicallyDeclaredNames of Block.

    -
    • - -
  • -

    It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the - VarDeclaredNames of Block.

    -
    • -
- -

NOTE An alternative static semantics for this production is given in B.3.3.

-
- -
-

13.14.2 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
TryStatement : try Block Catch
-
    -
  1. Let names be VarDeclaredNames of Block.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Catch.
    3. -
  3. Return names.
    4. -
-
TryStatement : try Block Finally
-
    -
  1. Let names be VarDeclaredNames of Block.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Finally.
    3. -
  3. Return names.
    4. -
-
TryStatement : try Block Catch Finally
-
    -
  1. Let names be VarDeclaredNames of Block.
    2. -
  2. Append to names the elements of the VarDeclaredNames of Catch.
    3. -
  3. Append to names the elements of the VarDeclaredNames of Finally.
    4. -
  4. Return names.
    5. -
-
Catch : catch ( CatchParameter ) Block
-
    -
  1. Return the VarDeclaredNames of Block.
    2. -
-
- -
-

13.14.3 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 14.1.18, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
TryStatement : try Block Catch
-
    -
  1. Let declarations be VarScopedDeclarations of Block.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Catch.
    3. -
  3. Return declarations.
    4. -
-
TryStatement : try Block Finally
-
    -
  1. Let declarations be VarScopedDeclarations of Block.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Finally.
    3. -
  3. Return declarations.
    4. -
-
TryStatement : try Block Catch Finally
-
    -
  1. Let declarations be VarScopedDeclarations of Block.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of Catch.
    3. -
  3. Append to declarations the elements of the VarScopedDeclarations of Finally.
    4. -
  4. Return declarations.
    5. -
-
Catch : catch ( CatchParameter ) Block
-
    -
  1. Return the VarScopedDeclarations of Block.
    2. -
-
- -
-

13.14.4 Runtime Semantics: BindingInitialization

- -

With arguments value and environment.

- -
-

NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for - var statements formal parameter lists of non-strict functions. In those cases a lexical binding is hosted and - preinitialized prior to evaluation of its initializer.

-
- -

See also: 12.2.4.2.2, Error! Reference source not found., 13.2.2.2, 13.2.3.4.

- -

CatchParameter : BindingPattern

- -
    -
  1. If Type(value) is not Object, then throw a TypeError - exception.
    2. -
  2. Return the result of performing BindingInitialization for BindingPattern passing value and - environment as the arguments.
    3. -
-
- -
-

13.14.5 Runtime Semantics: CatchClauseEvaluation

- -

with parameter thrownValue

- -
Catch : catch ( CatchParameter ) Block
-
    -
  1. Let oldEnv be the running execution context’s LexicalEnvironment.
    2. -
  2. Let catchEnv be NewDeclarativeEnvironment(oldEnv).
    3. -
  3. For each element argName of the BoundNames of CatchParameter, do -
      -
    1. Call the CreateMutableBinding concrete method of catchEnv passing argName as the argument.
      2. -
    2. Assert: The above call to CreateMutableBinding will never return an abrupt completion.
      3. -
    -
    4. -
  4. Let status be the result of performing BindingInitialization for CatchParameter passing - thrownValue and catchEnv as arguments.
    5. -
  5. ReturnIfAbrupt(status).
    6. -
  6. Set the running execution context’s LexicalEnvironment to catchEnv.
    7. -
  7. Let B be the result of evaluating Block.
    8. -
  8. Set the running execution context’s LexicalEnvironment to oldEnv.
    9. -
  9. Return B.
    10. -
- -
-

NOTE No matter how control leaves the Block the LexicalEnvironment is always restored to its former state.

-
-
- -
-

13.14.6 Runtime Semantics: Evaluation

-
TryStatement : try Block Catch
-
    -
  1. Let B be the result of evaluating Block.
    2. -
  2. If B.[[type]] is not throw, return B.
    3. -
  3. Return the result of performing CatchClauseEvaluation of Catch with parameter B.[[value]].
    4. -
-
TryStatement : try Block Finally
-
    -
  1. Let B be the result of evaluating Block.
    2. -
  2. Let F be the result of evaluating Finally.
    3. -
  3. If F.[[type]] is normal, return B.
    4. -
  4. Return F.
    5. -
-
TryStatement : try Block Catch Finally
-
    -
  1. Let B be the result of evaluating Block.
    2. -
  2. If B.[[type]] is throw, then -
      -
    1. Let C be the result of performing CatchClauseEvaluation of Catch with parameter - B.[[value]].
      2. -
    -
    3. -
  3. Else B.[[type]] is not throw, -
      -
    1. Let C be B.
      2. -
    -
    4. -
  4. Let F be the result of evaluating Finally.
    5. -
  5. If F.[[type]] is normal, return C.
    6. -
  6. Return F.
    7. -
-
-
- -
-
-

13.15 The - debugger statement

-

Syntax

- -
-
DebuggerStatement :
-
debugger ;
-
-
- -
-

13.15.1 Runtime Semantics: Evaluation

- -
-

NOTE Evaluating the DebuggerStatement production may allow an - implementation to cause a breakpoint when run under a debugger. If a debugger is not present or active this statement has - no observable effect.

-
- -
DebuggerStatement : debugger ;
-
    -
  1. If an implementation defined debugging facility is available and enabled, then -
      -
    1. Perform an implementation defined debugging action.
      2. -
    2. Let result be an implementation defined Completion - value.
      3. -
    -
    2. -
  2. Else -
      -
    1. Let result be NormalCompletion(empty).
      2. -
    -
    3. -
  3. Return result.
    4. -
-
-
-
- -
-
-

14 ECMAScript Language: Functions and Classes

- -
-

NOTE Various ECMAScript language elements cause the creation of ECMAScript function objects (9.1.14). Evaluation of such functions starts with the execution of their - [[Call]] internal method (Error! Reference source not found.).

-
-
- -
-
-

14.1 - Function Definitions

-

Syntax

- -
-
FunctionDeclaration[Yield, Default] :
-
function BindingIdentifier[?Yield, ?Default] ( FormalParameters ) { FunctionBody }
-
- -
-
FunctionExpression :
-
function BindingIdentifieropt ( FormalParameters ) { FunctionBody }
-
- -
-
StrictFormalParameters[Yield, GeneratorParameter] :
-
FormalParameters[?Yield, ?GeneratorParameter]
-
- -
-
FormalParameters[Yield,GeneratorParameter] :
-
[empty]
-
FormalParameterList[?Yield, ?GeneratorParameter]
-
- -
-
FormalParameterList[Yield,GeneratorParameter] :
-
FunctionRestParameter[?Yield]
-
FormalsList[?Yield, ?GeneratorParameter]
-
FormalsList[?Yield, ?GeneratorParameter] , FunctionRestParameter[?Yield]
-
- -
-
FormalsList[Yield,GeneratorParameter] :
-
FormalParameter[?Yield, ?GeneratorParameter]
-
FormalsList[?Yield, ?GeneratorParameter] , FormalParameter[?Yield,?GeneratorParameter]
-
- -
-
FunctionRestParameter[Yield] :
-
BindingRestElement[Yield]
-
- -
-
FormalParameter[Yield,GeneratorParameter] :
-
BindingElement[?Yield, ?GeneratorParameter]
-
- -
-
FunctionBody[Yield] :
-
FunctionStatementList[?Yield]
-
- -
-
FunctionStatementList[Yield] :
-
StatementList[?Yield, Return]opt
-
-
- -
-

14.1.1 Directive Prologues and the Use Strict Directive

- -

A Directive Prologue is the longest sequence of ExpressionStatement productions occurring as the - initial StatementListItem productions of a FunctionBody or a ScriptBody and where each ExpressionStatement in the sequence consists entirely of - a StringLiteral token followed by a semicolon. The - semicolon may appear explicitly or may be inserted by automatic semicolon - insertion. A Directive Prologue may be an empty sequence.

- -

A Use Strict Directive is an ExpressionStatement in a Directive Prologue whose StringLiteral is either the exact character sequences "use strict" or - 'use strict'. A Use Strict Directive may not contain an EscapeSequence or LineContinuation.

- -

A Directive Prologue may contain more than one Use Strict Directive. However, an implementation may issue a warning if - this occurs.

- -
-

NOTE The ExpressionStatement productions of a Directive Prologue are evaluated normally - during evaluation of the containing production. Implementations may define implementation specific meanings for - ExpressionStatement productions which are not a Use Strict Directive and which occur in a Directive Prologue. If - an appropriate notification mechanism exists, an implementation should issue a warning if it encounters in a Directive - Prologue an ExpressionStatement that is not a Use Strict Directive and which does not have a meaning defined by the - implementation.

-
-
- -
-

14.1.2 Static Semantics: Early Errors

- -

FunctionDeclaration : function - BindingIdentifier ( FormalParameters ) { FunctionBody }
and
FunctionExpression : - function BindingIdentifieropt ( FormalParameters ) { FunctionBody - }

- -
    -
  • -

    If the source code matching this production is strict code, the Early Error rules - for StrictFormalParameters : FormalParameters are applied.

    -
    • - -
  • -

    It is a Syntax Error if any element of the BoundNames of FormalParameters also occurs in the - LexicallyDeclaredNames of FunctionBody.

    -
    • -
- -
-

NOTE The LexicallyDeclaredNames of a FunctionBody does not include identifiers bound - using var or function declarations. Simple parameter lists bind identifiers as VarDeclaredNames. Parameter lists that - contain destructuring patterns, default value initializers, or a rest parameter bind identifiers as - LexicallyDeclaredNames.

-
- -
StrictFormalParameters : FormalParameters
-
    -
  • -

    It is a Syntax Error if BoundNames of FormalParameters contains any duplicate elements.

    -
    • -
-
FormalParameters : FormalParameterList
-
    -
  • -

    It is a Syntax Error if IsSimpleParameterList of FormalParameterList is false and BoundNames of - FormalParameterList contains any duplicate elements.

    -
    • -
- -
-

NOTE Multiple occurrences of the same Identifier in a FormalParamterList is only - allowed for non-strict functions and generator functions that have simple parameter lists.

-
- -
FunctionStatementList : StatementList
-
    -
  • -

    It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate entries.

    -
    • - -
  • -

    It is a Syntax Error if any element of the LexicallyDeclaredNames of StatementList also occurs in the - VarDeclaredNames of StatementList.

    -
    • -
-
- -
-

14.1.3 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
FormalParameters : [empty]
-
    -
  1. Return an empty List.
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. Let names be BoundNames of FormalsList.
    2. -
  2. Append to names the BoundNames of FunctionRestParameter.
    3. -
  3. Return names.
    4. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. Let names be BoundNames of FormalsList.
    2. -
  2. Append to names the elements of BoundNames of FormalParameter.
    3. -
  3. Return names.
    4. -
-
- -
-

14.1.4 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.2.5.2, 12.3.1.1, 14.2.3, 14.4.3, 14.5.4

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
FunctionExpression : function BindingIdentifieropt ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
- -
-

NOTE Static semantic rules that depend upon substructure generally do not look into function - definitions.

-
-
- -
-

14.1.5 Static Semantics: ContainsExpression

- -

See also: 13.2.3.2, 14.2.4.

- -
FormalParameters : [empty]
-
    -
  1. Return false.
    2. -
-
FormalParameterList : FunctionRestParameter
-
    -
  1. Return false.
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. Return ContainsExpression of FormalsList.
    2. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. If ContainsExpression of FormalsList is true, then return true.
    2. -
  2. Return ContainsExpression of FormalParameter.
    3. -
-
- -
-

14.1.6 Static Semantics: ExpectedArgumentCount

- -

See also: 14.2.6, 14.3.2.

- -
FormalParameters : [empty]
-
    -
  1. Return 0.
    2. -
-
FormalParameterList : FunctionRestParameter
-
    -
  1. Return 0.
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. Return the ExpectedArgumentCount of FormalsList.
    2. -
- -
-

NOTE The ExpectedArgumentCount of a FormalParameterList is the number of - FormalParameters to the left of either the rest parameter or the first FormalParameter with an Initializer. - A FormalParameter without an initializer is allowed after the first parameter with an initializer but such - parameters are considered to be optional with undefined as their default value.

-
- -
FormalsList : FormalParameter
-
    -
  1. If HasInitializer of FormalParameter is true return 0
    2. -
  2. Return 1.
    3. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. Let count be the ExpectedArgumentCount of FormalsList.
    2. -
  2. If HasInitializer of FormalsList is true or HasInitializer of FormalParameter is true, - then return count.
    3. -
  3. Return count+1.
    4. -
-
- -
-

14.1.7 Static Semantics: HasInitializer

- -

See also: 13.2.3.3, 14.2.7.

- -
FormalParameters : [empty]
-
    -
  1. Return false.
    2. -
-
FormalParameterList : FunctionRestParameter
-
    -
  1. Return false.
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. If HasInitializer of FormalsList is true, then return true.
    2. -
  2. Return false.
    3. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. If HasInitializer of FormalsList is true, then return true.
    2. -
  2. Return HasInitializer of FormalParameter.
    3. -
-
- -
-

14.1.8 Static Semantics: HasName

- -

See also: 14.2.8, 14.4.6, 14.5.6.

- -
FunctionExpression : function ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
FunctionExpression : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
- -
-

14.1.9 Static Semantics: IsAnonymousFunctionDefinition ( production) Abstract - Operation

- -

The abstract operation IsAnonymousFunctionDefinition determines if its argument is a function definition that does not - bind a name. The argument production is the result of parsing an AssignmentExpression or - Initializer. The following steps are taken:

- -
    -
  1. If IsFunctionDefinition of production is false, then return false.
    2. -
  2. Let hasName be the result of HasName of production.
    3. -
  3. If hasName is true, then return false.
    4. -
  4. Return true.
    5. -
-
- -
-

14.1.10 Static Semantics: IsConstantDeclaration

- -

See also: 13.2.1.3, 14.4.5, 14.5.5.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
- -
-

14.1.11 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.4.8, 14.5.8.

- -
FunctionExpression : function ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
FunctionExpression : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
- -
-

14.1.12 Static Semantics: IsSimpleParameterList

- -

See also: 13.2.3.4, 14.2.8

- -
FormalParameters : [empty]
-
    -
  1. Return true.
    2. -
-
FormalParameterList : FunctionRestParameter
-
    -
  1. Return false.
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. Return false.
    2. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. If IsSimpleParameterList of FormalsList is false, return false.
    2. -
  2. Return IsSimpleParameterList of FormalParameter.
    3. -
-
FormalParameter : BindingElement
-
    -
  1. Return IsSimpleParameterList of BindingElement.
    2. -
-
- -
-

14.1.13 Static Semantics: IsStrict

- -

See also: 15.1.2, 15.2.0.7.

- -
FunctionStatementList : StatementListopt
-
    -
  1. If this FunctionStatementList is contained in strict code or if - StatementList is strict code, then return true. Otherwise, return - false.
    2. -
-
- -
-

14.1.14 Static Semantics: LexicallyScopedDeclarations

- -

See also: 13.11.2, 15.2.0.11.

- -
FunctionStatementList : [empty]
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : StatementList
-
    -
  1. Return the TopLevelLexicallyScopedDeclarations of StatementList.
    2. -
-
- -
-

14.1.15 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.2.10, 14.4.8, 14.5.10, 15.1.3, 15.2.0.10.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
FunctionStatementList : [empty]
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : StatementList
-
    -
  1. Return TopLevelLexicallyDeclaredNames of StatementList.
    2. -
-
- -
-

14.1.16 Static Semantics: ReferencesSuper

- -

See also: 14.2.12, 14.3.6, 14.4.11.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If FormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
FunctionExpression : function BindingIdentifieropt ( FormalParameters ) { FunctionBody }
-
    -
  1. If FormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
FormalParameters : [empty]
-
    -
  1. Return false.
    2. -
-
FormalParameters : FormalParameterList
-
    -
  1. Return FormalParameterList Contains super.
    2. -
-
FunctionBody : FunctionStatementList
-
    -
  1. Return FunctionStatementList Contains super.
    2. -
-
- -
-

14.1.17 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : [empty]
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : StatementList
-
    -
  1. Return TopLevelVarDeclaredNames of StatementList.
    2. -
-
- -
-

14.1.18 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.2.14, 14.4.13, 15.1.6, 15.2.0.14.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : [empty]
-
    -
  1. Return an empty List.
    2. -
-
FunctionStatementList : StatementList
-
    -
  1. Return the TopLevelVarScopedDeclarations of StatementList.
    2. -
-
- -
-

14.1.19 Runtime Semantics: EvaluateBody

- -

With parameter functionObject.

- -

See also: 14.2.16, 14.4.13.

- -
FunctionBody : FunctionStatementList
-
    -
  1. The code of this FunctionBody is strict mode code if it is contained in strict mode code or if the Directive Prologue (14.1.1) of its FunctionStatementList contains - a Use Strict Directive or if any of the conditions - in 10.2.1 apply. If the code of this FunctionBody is strict mode code, FunctionStatementList is evaluated in the following steps as - strict mode code. Otherwise, StatementList is evaluated in the following - steps as non-strict mode code.
    2. -
  2. Let result be the result of evaluating FunctionStatementList.
    3. -
  3. If result.[[type]] is return then return NormalCompletion(result.[[value]])
    4. -
  4. ReturnIfAbrupt(result).
    5. -
  5. Return NormalCompletion(undefined).
    6. -
-
- -
-

14.1.20 Runtime Semantics: IteratorBindingInitialization

- -

With parameters iterator and environment.

- -
-

NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for - formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to - deal with the possibility of multiple parameters with the same name.

-
- -

See also: 13.2.3.6, - .

- -
FormalParameters : [empty]
-
    -
  1. Return NormalCompletion(empty).
    2. -
-
FormalParameterList : FormalsList , FunctionRestParameter
-
    -
  1. Let restIndex be the result of performing IteratorBindingInitialization for FormalsList using - iterator, and environment as the arguments.
    2. -
  2. ReturnIfAbrupt(restIndex).
    3. -
  3. Return the result of performing IteratorBindingInitialization for FunctionRestParameter using iterator - and environment as the arguments.
    4. -
-
FormalsList : FormalsList , FormalParameter
-
    -
  1. Let status be the result of performing IteratorBindingInitialization for FormalsList using - iterator and environment as the arguments.
    2. -
  2. ReturnIfAbrupt(status).
    3. -
  3. Return the result of performing IteratorBindingInitialization for FormalParameter using iterator and - environment as the arguments.
    4. -
-
- -
-

14.1.21 Runtime Semantics: InstantiateFunctionObject

- -

With parameter scope.

- -

See also: 14.4.15.

- -
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If the FunctionDeclaration is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Let name be StringValue of BindingIdentifier.
    3. -
  3. Let F be FunctionCreate(Normal, - FormalParameters, FunctionBody, scope, strict).
    4. -
  4. If ReferencesSuper of FunctionDeclaration is true, then -
      -
    1. Perform MakeMethod(F, name, undefined).
      2. -
    -
    5. -
  5. Perform MakeConstructor(F).
    6. -
  6. SetFunctionName(F, name).
    7. -
  7. Return F.
    8. -
-
- -
-

14.1.22 Runtime Semantics: Evaluation

-
FunctionDeclaration : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return NormalCompletion(empty)
    2. -
-
FunctionExpression : function ( FormalParameters ) { FunctionBody }
-
    -
  1. If the FunctionExpression is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Let scope be the LexicalEnvironment of the running execution context.
    3. -
  3. Let closure be FunctionCreate(Normal, FormalParameters, FunctionBody, scope, strict).
    4. -
  4. If ReferencesSuper of FunctionExpression is true, then -
      -
    1. Perform MakeMethod(closure, undefined, undefined).
      2. -
    -
    5. -
  5. Perform MakeConstructor(closure).
    6. -
  6. Return closure.
    7. -
-
FunctionExpression : function BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If the FunctionExpression is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Let runningContext be the running execution context’s Lexical Environment.
    3. -
  3. Let funcEnv be NewDeclarativeEnvironment(runningContext - ).
    4. -
  4. Let envRec be funcEnv’s environment record.
    5. -
  5. Let name be StringValue of BindingIdentifier.
    6. -
  6. Call the CreateImmutableBinding concrete method of envRec passing name as the argument.
    7. -
  7. Let closure be FunctionCreate(Normal, FormalParameters, FunctionBody, funcEnv, strict).
    8. -
  8. If ReferencesSuper of FunctionExpression is true, then -
      -
    1. Perform MakeMethod(closure, name, undefined).
      2. -
    -
    9. -
  9. Perform MakeConstructor(closure).
    10. -
  10. SetFunctionName(closure, name).
    11. -
  11. Call the InitializeBinding concrete method of envRec passing name and closure as the - arguments.
    12. -
  12. Return NormalCompletion(closure).
    13. -
- -
-

NOTE 1 The BindingIdentifier in a FunctionExpression can be referenced from - inside the FunctionExpression's FunctionBody to allow the function to call itself recursively. However, - unlike in a FunctionDeclaration, the BindingIdentifier in a FunctionExpression cannot be referenced - from and does not affect the scope enclosing the FunctionExpression.

-
- -
-

NOTE 2 A prototype property is automatically created for every function defined - using a FunctionDeclaration or FunctionExpression, to allow for the possibility that the function will be - used as a constructor.

-
- -
FunctionStatementList : [empty]
-
    -
  1. Return NormalCompletion(undefined).
    2. -
-
-
- -
-
-

14.2 Arrow Function Definitions

-

Syntax

- -
-
ArrowFunction[In, Yield] :
-
ArrowParameters[?Yield] [no LineTerminator here] => ConciseBody[?In]
-
- -
-
ArrowParameters[Yield] :
-
BindingIdentifier[?Yield]
-
CoverParenthesizedExpressionAndArrowParameterList[?Yield]
-
- -
-
ConciseBody[In] :
-
[lookahead ≠ { ] AssignmentExpression[?In]
-
{ FunctionBody }
-
- -

Supplemental Syntax

- -

When processing the production

- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -

is recognized the following grammar is used to refine the interpretation of CoverParenthesizedExpressionAndArrowParameterList :

- -
-
ArrowFormalParameters[Yield, GeneratorParameter] :
-
( StrictFormalParameters[?Yield, ?GeneratorParameter] )
-
-
- -
-

14.2.1 Static Semantics: Early Errors

-
ArrowFunction : ArrowParameters => ConciseBody
-
    -
  • -

    It is a Syntax Error if any element of the BoundNames of ArrowParameters also occurs in the - LexicallyDeclaredNames of ConciseBody.

    -
    • -
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  • -

    If the [Yield] grammar parameter is present on ArrowParameters, it is a Syntax Error if the - lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList[?Yield] cannot be - parsed with no tokens left over using ArrowFormalParameters[Yield, GeneratorParameter] as the goal - symbol.

    -
    • - -
  • -

    If the [Yield] grammar parameter is not present on ArrowParameters, it is a Syntax Error if the - lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList[?Yield] cannot be - parsed with no tokens left over using ArrowFormalParameters as the goal symbol.

    -
    • - -
  • -

    It is a Syntax Error if any early errors are present for CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].

    -
    • -
-
- -
-

14.2.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.1.3, 14.4.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return the BoundNames of formals.
    3. -
-
- -
-

14.2.3 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.2.5.2, 12.3.1.1, 14.1.4, 14.4.3, 14.5.4

- -
ArrowFunction : ArrowParameters => ConciseBody
-
    -
  1. If symbol is neither super nor this, then return false.
    2. -
  2. If ArrowParameters Contains symbol is true, return true;
    3. -
  3. Return ConciseBody Contains symbol .
    4. -
- -
-

NOTE Normally, Contains does not look inside most function forms However, Contains is used to detect this and - super usage within an ArrowFunction.

-
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return formals Contains symbol.
    3. -
-
- -
-

14.2.4 Static Semantics: ContainsExpression

- -

See also: 13.2.3.2, 14.1.5.

- -
ArrowParameters : BindingIdentifier
-
    -
  1. Return false.
    2. -
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return the ContainsExpression of formals.
    3. -
-
- -
-

14.2.5 Static Semantics: CoveredFormalsList

-
ArrowParameters : BindingIdentifier
-
    -
  1. Return BindingIdentifier.
    2. -
- -
-
CoverParenthesizedExpressionAndArrowParameterList[Yield] :
-
( Expression )
-
( )
-
( ... BindingIdentifier )
-
( Expression , ... BindingIdentifier )
-
- -
    -
  1. If the [Yield] grammar parameter is present for - CoverParenthesizedExpressionAndArrowParameterList[Yield] return the result of parsing the lexical - token stream matched by CoverParenthesizedExpressionAndArrowParameterList[Yield] using - ArrowFormalParameters[Yield, GeneratorParameter] as the goal symbol.
    2. -
  2. If the [Yield] grammar parameter is not present for - CoverParenthesizedExpressionAndArrowParameterList[Yield] return the result of parsing the lexical - token stream matched by CoverParenthesizedExpressionAndArrowParameterList using ArrowFormalParameters as - the goal symbol.
    3. -
-
- -
-

14.2.6 Static Semantics: ExpectedArgumentCount

- -

See also: 14.1.5, 14.3.2.

- -
ArrowParameters : BindingIdentifier
-
    -
  1. Return 1.
    2. -
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return the ExpectedArgumentCount of formals.
    3. -
-
- -
-

14.2.7 Static Semantics: HasInitializer

- -

See also: 13.2.3.3, 14.1.7.

- -
ArrowParameters : BindingIdentifier
-
    -
  1. Return false.
    2. -
-
ArrowParameters : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  1. Let formals be CoveredFormalsList of CoverParenthesizedExpressionAndArrowParameterList.
    2. -
  2. Return the HasInitializer of formals.
    3. -
-
- -
-

14.2.8 Static Semantics: HasName

- -

See also: 14.1.8, 14.4.6, 14.5.6.

- -
ArrowFunction : ArrowParameters => ConciseBody
-
    -
  1. Return false.
    2. -
-
- -
-

14.2.9 Static Semantics: IsSimpleParameterList

- -

See also: 13.2.3.4, 14.1.11.

- -
ArrowParameters : BindingIdentifier
-
    -
  1. Return true.
    2. -
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return the IsSimpleParameterList of formals.
    3. -
-
- -
-

14.2.10 Static Semantics: LexicallyScopedDeclarations

- -

See also: 13.11.2, 15.2.0.11.

- -
ConciseBody : AssignmentExpression
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.2.11 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.1.14, 14.4.8, 14.5.10, 15.1.3, 15.2.0.10.

- -
ConciseBody : AssignmentExpression
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.2.12 Static Semantics: ReferencesSuper

- -

See also: 14.1.16, 14.3.6, 14.4.11.

- -
ArrowFunction : ArrowParameters => ConciseBody
-
    -
  1. Return false.
    2. -
- -
-

NOTE ReferencesSuper is used to determine whether a function requires its own super bindings. - This is never the case for Arrow Functions.

-
-
- -
-

14.2.13 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.4.12, 14.5.15, 15.1.5, 15.2.0.13.

- -
ConciseBody : AssignmentExpression
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.2.14 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.4.13, 15.1.6, 15.2.0.14.

- -
ConciseBody : AssignmentExpression
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.2.15 Runtime Semantics: IteratorBindingInitialization

- -

With parameters iterator and environment.

- -

See also: 12.2.4.2.2, Error! Reference source not found.,13.2.2.2,13.2.3.4,13.14.3, 14.1.20.

- -
-

NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for - formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to - deal with the possibility of multiple parameters with the same name.

-
- -
ArrowParameters : BindingIdentifier
-
    -
  1. Let next be IteratorStep(iterator).
    2. -
  2. ReturnIfAbrupt(next).
    3. -
  3. If next is false, then let v be undefined
    4. -
  4. Else -
      -
    1. Let v be IteratorValue(next).
      2. -
    2. ReturnIfAbrupt(v).
      3. -
    -
    5. -
  5. Return the result of performing BindingInitialization for BindingIdentifier using v and - environment as the arguments.
    6. -
- -

ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]

- -
    -
  1. Let formals be CoveredFormalsList of - CoverParenthesizedExpressionAndArrowParameterList[?Yield].
    2. -
  2. Return the result of performing IteratorBindingInitialization of formals with arguments iterator and - environment.
    3. -
-
- -
-

14.2.16 Runtime Semantics: EvaluateBody

- -

With parameter functionObject.

- -

See also: 14.1.18, 14.4.13.

- -
ConciseBody : AssignmentExpression
-
    -
  1. The code of this ConciseBody is strict mode code if it is contained in strict mode code or if any of the conditions in 10.2.1 apply. If the code of this ConciseBody is strict mode code, AssignmentExpression is evaluated in the following steps as - strict mode code. Otherwise, AssignmentExpression is evaluated in the - following steps as non-strict mode code.
    2. -
  2. Let exprRef be the result of evaluating AssignmentExpression.
    3. -
  3. Let exprValue be GetValue(exprRef).
    4. -
  4. If exprValue.[[type]] is return then return NormalCompletion(exprValue.[[value]]).
    5. -
  5. ReturnIfAbrupt(exprValue).
    6. -
  6. Return NormalCompletion(exprValue).
    7. -
- -
-

NOTE In the absence of extensions to this specification, the test is step 4 will never be - true.

-
-
- -
-

14.2.17 Runtime Semantics: Evaluation

- -

ArrowFunction[Yield] : - ArrowParameters[?Yield] => - ConciseBody

- -
    -
  1. If the code of this ArrowFunction is contained in strict mode code or if - any of the conditions in 10.2.1 apply, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Let scope be the LexicalEnvironment of the running execution context.
    3. -
  3. Let parameters be CoveredFormalsList of ArrowParameters[?Yield].
    4. -
  4. Let closure be FunctionCreate(Arrow, parameters, ConciseBody, scope, strict).
    5. -
  5. Return closure.
    6. -
- -
-

NOTE Any reference to arguments, super, or this within - an ArrowFunction are resoved to their bindings in the lexically enclosing function. Even though an - ArrowFunction may contain references to super, the function object created in step 4 is not made into - a method by performing MakeMethod. An ArrowFunction that references - super is always contained within a non-ArrowFunction and the necessary state to implement - super is accessible via the scope that is captured by the function object of the - ArrowFunction.

-
-
-
- -
-
-

14.3 Method - Definitions

-

Syntax

- -
-
MethodDefinition[Yield] :
-
PropertyName[?Yield] ( StrictFormalParameters ) { FunctionBody }
-
GeneratorMethod[?Yield]
-
get PropertyName[?Yield] ( ) { FunctionBody }
-
set PropertyName[?Yield] ( PropertySetParameterList ) { FunctionBody }
-
- -
-
PropertySetParameterList :
-
FormalParameter
-
-
- -
-

14.3.1 Static Semantics: Early Errors

-
MethodDefinition : PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  • -

    It is a Syntax Error if any element of the BoundNames of StrictFormalParameters also occurs in the - LexicallyDeclaredNames of FunctionBody.

    -
    • -
-
MethodDefinition : set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
    -
  • -

    It is a Syntax Error if BoundNames of PropertySetParameterList contains any duplicate elements.

    -
    • - -
  • -

    It is a Syntax Error if any element of the BoundNames of PropertySetParameterList also occurs in the - LexicallyDeclaredNames of FunctionBody.

    -
    • -
-
- -
-

14.3.2 Static Semantics: ComputedPropertyContains

- -

With parameter symbol.

- -

See also: 12.2.5.2, 14.4.3, 14.5.5.

- -
-
MethodDefinition :
-
PropertyName ( StrictFormalParameters ) { FunctionBody }
-
get PropertyName ( ) { FunctionBody }
-
set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
- -
    -
  1. Return the result of ComputedPropertyContains for PropertyName with argument symbol.
    2. -
-
- -
-

14.3.3 Static Semantics: ExpectedArgumentCount

- -

See also: 14.1.5, 14.2.6.

- -
PropertySetParameterList : FormalParameter
-
    -
  1. If HasInitializer of FormalParameter is true return 0
    2. -
  2. Return 1.
    3. -
-
- -
-

14.3.4 Static Semantics: HasComputedPropertyKey

- -

See also: 12.2.5.4, 14.4.5

- -
-
MethodDefinition :
-
PropertyName ( StrictFormalParameters ) { FunctionBody }
-
get PropertyName ( ) { FunctionBody }
-
set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
- -
    -
  1. Return HasComputedPropertyKey of PropertyName.
    2. -
-
- -
-

14.3.5 Static Semantics: PropName

- -

See also: 12.2.5.6, 14.4.10, 14.5.13

- -
-
MethodDefinition :
-
PropertyName ( StrictFormalParameters ) { FunctionBody }
-
get PropertyName ( ) { FunctionBody }
-
set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
- -
    -
  1. Return PropName of PropertyName.
    2. -
-
- -
-

14.3.6 Static Semantics: ReferencesSuper

- -

See also: 14.1.16, 14.2.12, 14.4.11.

- -
MethodDefinition : PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. If StrictFormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
MethodDefinition : get PropertyName ( ) { FunctionBody }
-
    -
  1. Return FunctionBody Contains super.
    2. -
-
MethodDefinition : set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
    -
  1. If PropertySetParameterList Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
- -
-

14.3.7 Static Semantics: SpecialMethod

-
MethodDefinition : PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
- -
-
MethodDefinition :
-
GeneratorMethod
-
get PropertyName ( ) { FunctionBody }
-
set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
- -
    -
  1. Return true.
    2. -
-
- -
-

14.3.8 Runtime Semantics: DefineMethod

- -

With parameters object and optional parameter functionPrototype.

- -
MethodDefinition : PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let strict be IsStrict of FunctionBody.
    4. -
  4. Let scope be the running execution context’s LexicalEnvironment.
    5. -
  5. Let closure be FunctionCreate(Method, StrictFormalParameters, FunctionBody, scope, strict). If - functionPrototype was passed as a parameter then pass its value as the functionPrototype optional - argument of FunctionCreate.
    6. -
  6. If ReferencesSuper of MethodDefinition is true, then -
      -
    1. Perform MakeMethod(closure, propKey, object).
      2. -
    -
    7. -
  7. Return the Record{[[key]]: propKey, [[closure]]: closure}.
    8. -
-
- -
-

14.3.9 Runtime Semantics: PropertyDefinitionEvaluation

- -

With parameter object.

- -

See also: 12.2.5.9, 14.4.16, B.3.1

- -
MethodDefinition : PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Let methodDef be the result of DefineMethod of this MethodDefinition with argument object.
    2. -
  2. ReturnIfAbrupt(methodDef).
    3. -
  3. SetFunctionName(methodDef.[[closure]], methodDef.[[key]]).
    4. -
  4. Let desc be the Property Descriptor{[[Value]]: - methodDef.[[closure]], [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: - true}.
    5. -
  5. Return DefinePropertyOrThrow(object, methodDef.[[key]], - desc).
    6. -
-
MethodDefinition : GeneratorMethod
- -

See 14.4.

- -
MethodDefinition : get PropertyName ( ) { FunctionBody }
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let strict be IsStrict of FunctionBody.
    4. -
  4. Let scope be the running execution context’s LexicalEnvironment.
    5. -
  5. Let formalParameterList be the production FormalParameters : [empty]
    6. -
  6. Let closure be FunctionCreate(Method, formalParameterList, FunctionBody, scope, strict).
    7. -
  7. If ReferencesSuper of MethodDefinition is true, then -
      -
    1. Perform MakeMethod(closure, propKey, object).
      2. -
    -
    8. -
  8. SetFunctionName(closure, propKey, "get").
    9. -
  9. Let desc be the PropertyDescriptor{[[Get]]: closure, [[Enumerable]]: true, [[Configurable]]: - true}
    10. -
  10. Return DefinePropertyOrThrow(object, propKey, - desc).
    11. -
-
MethodDefinition : set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let strict be IsStrict of FunctionBody.
    4. -
  4. Let scope be the running execution context’s LexicalEnvironment.
    5. -
  5. Let closure be FunctionCreate(Method, PropertySetParameterList, FunctionBody, scope, strict).
    6. -
  6. If ReferencesSuper of MethodDefinition is true, then -
      -
    1. Perform MakeMethod(closure, propKey, object).
      2. -
    -
    7. -
  7. SetFunctionName(closure, propKey, "set").
    8. -
  8. Let desc be the PropertyDescriptor{[[Set]]: closure, [[Enumerable]]: true, [[Configurable]]: - true}
    9. -
  9. Return DefinePropertyOrThrow(object, propKey, - desc).
    10. -
-
-
- -
-
-

14.4 Generator Function Definitions

-

Syntax

- -
-
GeneratorMethod[Yield] :
-
* PropertyName[?Yield] ( StrictFormalParameters[Yield,GeneratorParameter] ) { FunctionBody[Yield] }
-
- -
-
GeneratorDeclaration[Yield, Default] :
-
function * BindingIdentifier[?Yield, ?Default] ( FormalParameters[Yield,GeneratorParameter] ) { FunctionBody[Yield] }
-
- -
-
GeneratorExpression :
-
function * BindingIdentifier[Yield]opt ( FormalParameters[Yield,GeneratorParameter] ) { FunctionBody[Yield] }
-
- -
-
YieldExpression[In] :
-
yield
-
yield [no LineTerminator here] [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]
-
yield [no LineTerminator here] * [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]
-
- -
-

NOTE YieldExpression cannot be used within the FormalParameters of a generator - function because any expressions that are part of FormalParameters are evaluate before the resulting generator - object is in a resumable state.

-
- -

Supplemental Syntax

- -

The following productions are used as an aid in specifying the semantics of certain ECMAScript language features. They - are not used when parsing ECMAScript source code.

- -
-
GeneratorBody :
-
FunctionBody
-
Comprehension
-
- -
-

NOTE: Abstract operations relating to generator objects are defined in 25.3.3.

-
-
- -
-

14.4.1 Static Semantics: Early Errors

-
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  • -

    It is a Syntax Error if any element of the BoundNames of StrictFormalParameters also occurs in the - LexicallyDeclaredNames of FunctionBody.

    -
    • -
- -

GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody - }
and
GeneratorExpression : function * BindingIdentifieropt ( FormalParameters ) { FunctionBody }

- -

If the source code matching this production is strict code, the Early Error rules for - StrictFormalParameters : FormalParameters are applied.

- -
    -
  • -

    It is a Syntax Error if any element of the BoundNames of FormalParameters also occurs in the - LexicallyDeclaredNames of FunctionBody.

    -
    • -
-
- -
-

14.4.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.5.2, 15.2.1.2, 15.2.2.1.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
- -
-

14.4.3 Static Semantics: ComputedPropertyContains

- -

With parameter symbol.

- -

See also: 12.2.5.2, 14.3.2, 14.5.5.

- -
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Return the result of ComputedPropertyContains for PropertyName with argument symbol.
    2. -
-
- -
-

14.4.4 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.2.5.2, 12.3.1.1, 14.1.4, 14.2.3, 14.5.4

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
GeneratorExpression : function * BindingIdentifieropt ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
- -
-

NOTE Static semantic rules that depend upon substructure generally do not look into function - definitions.

-
-
- -
-

14.4.5 Static Semantics: HasComputedPropertyKey

- -

See also: 12.2.5.4, 14.3.4

- -
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Return IsComputedPropertyKey of PropertyName.
    2. -
-
- -
-

14.4.6 Static Semantics: HasName

- -

See also: 14.1.8, 14.2.8, 14.5.6.

- -
GeneratorExpression : function * ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
GeneratorExpression : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
- -
-

14.4.7 Static Semantics: IsConstantDeclaration

- -

See also: 13.2.1.3, 14.1.8, 14.5.5.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return false.
    2. -
-
- -
-

14.4.8 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.5.8.

- -
GeneratorExpression : function * ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
GeneratorExpression : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return true.
    2. -
-
- -
-

14.4.9 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.1.14, 14.2.10, 14.5.10, 15.1.3, 15.2.0.10.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
- -
-

14.4.10 Static Semantics: PropName

- -

See also: 12.2.5.6, 14.3.5, 14.5.13

- -
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Return PropName of PropertyName.
    2. -
-
- -
-

14.4.11 Static Semantics: ReferencesSuper

- -

See also: 14.1.16,14.2.12, 14.3.6.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If FormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
GeneratorExpression : function * BindingIdentifieropt ( FormalParameters ) { FunctionBody }
-
    -
  1. If FormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. If StrictFormalParameters Contains super is true, then return true.
    2. -
  2. Return FunctionBody Contains super.
    3. -
-
- -
-

14.4.12 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.5.15, 15.1.5, 15.2.0.13.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.4.13 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 15.1.6, 15.2.0.14.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return an empty List.
    2. -
-
- -
-

14.4.14 Runtime Semantics: EvaluateBody

- -

With parameter functionObject.

- -

See also: 14.1.18, 14.2.16.

- -
GeneratorBody : FunctionBody
-
    -
  1. Assert: A Function Environment - Record containing a this binding has already been activated.
    2. -
  2. Let env be GetThisEnvironment( ).
    3. -
  3. Let G be the result of calling the GetThisBinding concrete method of env.
    4. -
  4. If Type(G) is not Object or if Type(G) is Object and G does not have a - [[GeneratorState]] internal slot or if Type(G) is Object and G has a [[GeneratorState]] internal slot and the value of G’s - [[GeneratorState]] internal slot is not - undefined, then -
      -
    1. Let newG be OrdinaryCreateFromConstructor(functionObject, - "%GeneratorPrototype%", ( [[GeneratorState]], [[GeneratorContext]]) ).
      2. -
    2. ReturnIfAbrupt(newG).
      3. -
    3. Let G be newG.
      4. -
    -
    5. -
  5. Return GeneratorStart(G, FunctionBody).
    6. -
-
GeneratorBody : Comprehension
-
    -
  1. Let G be ObjectCreate(%GeneratorPrototype%, ( [[GeneratorState]], [[GeneratorContext]]) ).
    2. -
  2. ReturnIfAbrupt(G).
    3. -
  3. Assert: the value of G’s [[GeneratorState]] internal slot is undefined.
    4. -
  4. Let startStatus be GeneratorStart(G, Comprehension).
    5. -
  5. ReturnIfAbrupt(startStatus).
    6. -
  6. Return G.
    7. -
-
- -
-

14.4.15 Runtime Semantics: InstantiateFunctionObject

- -

With parameter scope.

- -

See also: 14.1.21.

- -
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If the GeneratorDeclaration is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Let name be StringValue of BindingIdentifier.
    3. -
  3. Using FunctionBody from the production that is being evaluated, let body be the supplemental syntactic - grammar production: GeneratorBody : FunctionBody .
    4. -
  4. Let F be GeneratorFunctionCreate(Normal, FormalParameters, body, scope, strict).
    5. -
  5. If ReferencesSuper of GeneratorDeclaration is true, then -
      -
    1. Perform MakeMethod(F, name, undefined).
      2. -
    -
    6. -
  6. Let prototype be ObjectCreate(%GeneratorPrototype%).
    7. -
  7. Perform MakeConstructor(F, true, prototype).
    8. -
  8. SetFunctionName(F, name).
    9. -
  9. Return F.
    10. -
-
- -
-

14.4.16 Runtime Semantics: PropertyDefinitionEvaluation

- -

With parameter object.

- -

See also: 12.2.5.9, 14.3.9, B.3.1

- -
GeneratorMethod : * PropertyName ( StrictFormalParameters ) { FunctionBody }
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let strict be IsStrict of FunctionBody.
    4. -
  4. Let scope be the running execution context’s LexicalEnvironment.
    5. -
  5. Using FunctionBody from the production that is being evaluated, let body be the supplemental syntactic - grammar production: GeneratorBody : FunctionBody .
    6. -
  6. Let closure be GeneratorFunctionCreate(Method, StrictFormalParameters, body, scope, strict).
    7. -
  7. If ReferencesSuper of GeneratorMethod is true, then -
      -
    1. Perform MakeMethod(closure, propKey, object).
      2. -
    -
    8. -
  8. Let prototype be ObjectCreate(%GeneratorPrototype%).
    9. -
  9. Perform MakeConstructor(closure, true, prototype).
    10. -
  10. SetFunctionName(closure, propKey).
    11. -
  11. Let desc be the Property Descriptor{[[Value]]: - closure, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true}.
    12. -
  12. Return DefinePropertyOrThrow(object, propKey, - desc).
    13. -
-
- -
-

14.4.17 Runtime Semantics: Evaluation

-
GeneratorDeclaration : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. Return NormalCompletion(empty)
    2. -
-
GeneratorExpression : function * ( FormalParameters ) { FunctionBody }
-
    -
  1. If the GeneratorExpression is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Using FunctionBody from the production that is being evaluated, let body be the supplemental syntactic - grammar production: GeneratorBody : FunctionBody .
    3. -
  3. Let scope be the LexicalEnvironment of the running execution context.
    4. -
  4. Let closure be GeneratorFunctionCreate(Normal, FormalParameters, body, scope, strict).
    5. -
  5. If ReferencesSuper of GeneratorExpression is true, then -
      -
    1. Perform MakeMethod(closure, undefined, undefined).
      2. -
    -
    6. -
  6. Let prototype be ObjectCreate(%GeneratorPrototype%).
    7. -
  7. Perform MakeConstructor(closure, true, prototype).
    8. -
  8. Return closure.
    9. -
-
GeneratorExpression : function * BindingIdentifier ( FormalParameters ) { FunctionBody }
-
    -
  1. If the GeneratorExpression is contained in strict code or if its - FunctionBody is strict code, then let strict be true. - Otherwise let strict be false.
    2. -
  2. Using FunctionBody from the production that is being evaluated, let body be the supplemental syntactic - grammar production: GeneratorBody : FunctionBody .
    3. -
  3. Let runningContext be the running execution context’s Lexical Environment.
    4. -
  4. Let funcEnv be NewDeclarativeEnvironment(runningContext).
    5. -
  5. Let envRec be funcEnv’s environment record.
    6. -
  6. Let name be StringValue of BindingIdentifier.
    7. -
  7. Call the CreateImmutableBinding concrete method of envRec passing name as the argument.
    8. -
  8. Let closure be GeneratorFunctionCreate(Normal, FormalParameters, body, funcEnv, strict).
    9. -
  9. If ReferencesSuper of GeneratorExpression is true, then -
      -
    1. Perform MakeMethod(closure, name, undefined).
      2. -
    -
    10. -
  10. Let prototype be ObjectCreate(%GeneratorPrototype%).
    11. -
  11. Perform MakeConstructor (closure, true, prototype).
    12. -
  12. SetFunctionName(closure, name).
    13. -
  13. Call the InitializeBinding concrete method of envRec passing name and closure as the - arguments.
    14. -
  14. Return closure.
    15. -
- -
-

NOTE 1 The BindingIdentifier in a GeneratorExpression can be referenced from - inside the GeneratorExpression's FunctionBody to allow the generator code to call itself recursively. - However, unlike in a GeneratorDeclaration, the BindingIdentifier in a GeneratorExpression cannot be - referenced from and does not affect the scope enclosing the GeneratorExpression.

-
- -
YieldExpression : yield
-
    -
  1. Return GeneratorYield(CreateIterResultObject(undefined, false)).
    2. -
-
YieldExpression : yield AssignmentExpression
-
    -
  1. Let exprRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let value be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. Return GeneratorYield(CreateIterResultObject(value, false)).
    5. -
-
YieldExpression : yield * AssignmentExpression
-
    -
  1. Let exprRef be the result of evaluating AssignmentExpression.
    2. -
  2. Let value be GetValue(exprRef).
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. Let iterator be GetIterator(value).
    5. -
  5. ReturnIfAbrupt(iterator).
    6. -
  6. Let received be NormalCompletion(undefined).
    7. -
  7. Repeat -
      -
    1. If received.[[type]] is normal, then -
        -
      1. Let innerResult be IteratorNext(iterator, - received.[[value]]).
        2. -
      2. ReturnIfAbrupt(innerResult).
        3. -
      -
      2. -
    2. Else -
        -
      1. Assert: received.[[type]] is throw.
        2. -
      2. If HasProperty(iterator, "throw") is true, then -
          -
        1. Let innerResult be Invoke(iterator, "throw", - (received.[[value]])).
          2. -
        2. ReturnIfAbrupt(innerResult).
          3. -
        3. If Type(innerResult) is not Object, then throw - a TypeError exception.
          4. -
        -
        3. -
      3. Else, return received.
        4. -
      -
      3. -
    3. Let done be IteratorComplete(innerResult).
      4. -
    4. ReturnIfAbrupt(done).
      5. -
    5. If done is true, then -
        -
      1. Return IteratorValue (innerResult).
        2. -
      -
      6. -
    6. Let received be GeneratorYield(innerResult).
      7. -
    -
    8. -
-
-
- -
-
-

14.5 Class - Definitions

-

Syntax

- -
-
ClassDeclaration[Yield, Default] :
-
class BindingIdentifier[?Yield, ?Default] ClassTail[?Yield]
-
- -
-
ClassExpression[Yield,GeneratorParameter] :
-
class BindingIdentifier[?Yield]opt ClassTail[?Yield,?GeneratorParameter]
-
- -
-
ClassTail[Yield,GeneratorParameter] :
-
[~GeneratorParameter] ClassHeritage[?Yield]opt { ClassBody[?Yield]opt }
-
[+GeneratorParameter] ClassHeritageopt { ClassBodyopt }
-
- -
-
ClassHeritage[Yield] :
-
extends LeftHandSideExpression[?Yield]
-
- -
-
ClassBody[Yield] :
-
ClassElementList[?Yield]
-
- -
-
ClassElementList[Yield] :
-
ClassElement[?Yield]
-
ClassElementList[?Yield] ClassElement[?Yield]
-
- -
-
ClassElement[Yield] :
-
MethodDefinition[?Yield]
-
static MethodDefinition[?Yield]
-
;
-
- -
-

NOTE A ClassBody is always strict code.

-
-
- -
-

14.5.1 Static Semantics: Early Errors

- -

ClassDeclaration : class BindingIdentifier ClassTail

- -

ClassExpression : class BindingIdentifier ClassTail

- -
    -
  • It is a Syntax Error if the StringValue of BindingIdentifier is "let".
    • -
-
ClassBody : ClassElementList
-
    -
  • -

    It is a Syntax Error if PrototypePropertyNameList of ClassElementList contains any duplicate entries, - unless the following condition is true for each duplicate entry: The duplicated entry occurs exactly twice in - the list and one occurrence was obtained from a get accessor MethodDefinition and the other - occurrence was obtained from a set accessor MethodDefinition.

    -
    • - -
  • -

    It is a Syntax Error if StaticPropertyNameList of ClassElementList contains any duplicate entries, unless - the following condition is true for each duplicate entry: The duplicated entry occurs exactly twice in - the list and one occurrence was obtained from a get accessor MethodDefinition and the other - occurrence was obtained from a set accessor MethodDefinition.

    -
    • -
-
ClassElement : MethodDefinition
-
    -
  • -

    It is a Syntax Error if PropName of MethodDefinition is ″constructor″ and - SpecialMethod of MethodDefinition is true.

    -
    • -
-
ClassElement : static MethodDefinition
-
    -
  • It is a Syntax Error if PropName of MethodDefinition is ″prototype″.
    • -
-
- -
-

14.5.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 15.2.1.2, 15.2.2.1.

- -
ClassDeclaration : class BindingIdentifier ClassTail
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
- -
-

14.5.3 Static Semantics: ConstructorMethod

-
ClassElementList : ClassElement
-
    -
  1. If ClassElement is the production ClassElement : ; then, return empty.
    2. -
  2. If IsStatic of ClassElement is true, return empty.
    3. -
  3. If PropName of ClassElement is not ″constructor″, return - empty.
    4. -
  4. Return ClassElement.
    5. -
-
ClassElementList : ClassElementList ClassElement
-
    -
  1. Let head be ConstructorMethod of ClassElementList.
    2. -
  2. If head is not empty, return head.
    3. -
  3. If ClassElement is the production ClassElement : ; then, return empty.
    4. -
  4. If IsStatic of ClassElement is true, return empty.
    5. -
  5. If PropName of ClassElement is not ″constructor″, return - empty.
    6. -
  6. Return ClassElement.
    7. -
- -
-

NOTE Early Error rules ensure that there is only one method definition named ″constructor″ and that it is not an accessor property or generator definition.

-
-
- -
-

14.5.4 Static Semantics: Contains

- -

With parameter symbol.

- -

See also: 5.3, 12.2.5.2, 12.3.1.1, 14.1.4, 14.2.3, 14.4.3

- -
ClassTail : ClassHeritageopt { ClassBody }
-
    -
  1. If symbol is ClassBody, return true.
    2. -
  2. If symbol is ClassHeritage, then -
      -
    1. If ClassHeritage is present, return true otherwise return false.
      2. -
    -
    3. -
  3. Let inHeritage be ClassHeritage Contains symbol.
    4. -
  4. If inHeritage is true, then return true.
    5. -
  5. Return the result of ComputedPropertyContains for ClassBody with argument symbol.
    6. -
- -
-

NOTE Static semantic rules that depend upon substructure generally do not look into class - bodies except for PropertyName productions.

-
-
- -
-

14.5.5 Static Semantics: ComputedPropertyContains

- -

With parameter symbol.

- -

See also: 12.2.5.2, 14.3.2, 14.4.3.

- -
ClassElementList : ClassElementList ClassElement
-
    -
  1. Let inList be the result of ComputedPropertyContains for ClassElementList with argument - symbol.
    2. -
  2. If inList is true, then return true.
    3. -
  3. Return the result of ComputedPropertyContains for ClassElement with argument symbol.
    4. -
-
ClassElement : MethodDefinition
-
    -
  1. Return the result of ComputedPropertyContains for MethodDefinition with argument symbol.
    2. -
-
ClassElement : static MethodDefinition
-
    -
  1. Return the result of ComputedPropertyContains for MethodDefinition with argument symbol.
    2. -
-
ClassElement : ;
-
    -
  1. Return false.
    2. -
-
- -
-

14.5.6 Static Semantics: HasName

- -

See also: 14.1.8, 14.2.8, 14.4.6.

- -
ClassExpression : class ClassTail
-
    -
  1. Return false.
    2. -
-
ClassExpression : class BindingIdentifier ClassTail
-
    -
  1. Return true.
    2. -
-
- -
-

14.5.7 Static Semantics: IsConstantDeclaration

- -

See also: 13.2.1.3, 14.1.8, 14.4.5.

- -
ClassDeclaration : class BindingIdentifier ClassTail
-
    -
  1. Return false.
    2. -
-
- -
-

14.5.8 Static Semantics: IsFunctionDefinition

- -

See also: 12.2.0.2, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.8.

- -
ClassExpression : class ClassTail
-
    -
  1. Return true.
    2. -
-
ClassExpression : class BindingIdentifier ClassTail
-
    -
  1. Return true.
    2. -
-
- -
-

14.5.9 Static Semantics: IsStatic

-
ClassElement : MethodDefinition
-
    -
  1. Return false.
    2. -
-
ClassElement : static MethodDefinition
-
    -
  1. Return true.
    2. -
-
ClassElement : ;
-
    -
  1. Return false.
    2. -
-
- -
-

14.5.10 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.1.14, 14.2.10, 14.4.8, 15.1.3, 15.2.0.10.

- -
ClassDeclaration : class BindingIdentifier ClassTail
-
    -
  1. Return the BoundNames of BindingIdentifier.
    2. -
-
- -
-

14.5.11 Static Semantics: NonConstructorMethodDefinitions

-
ClassElementList : ClassElement
-
    -
  1. If ClassElement is the production ClassElement : ; then, return a new empty List.
    2. -
  2. If PropName of ClassElement is ″constructor″, return a - new empty List.
    3. -
  3. Return a List containing ClassElement.
    4. -
-
ClassElementList : ClassElementList ClassElement
-
    -
  1. Let list be PrototypeMethodDefinitions of ClassElementList.
    2. -
  2. If ClassElement is the production ClassElement : ; then, return list.
    3. -
  3. If IsStatic of ClassElement is false and PropName of ClassElement is ″constructor″, return - list.
    4. -
  4. Append ClassElement to the end of list.
    5. -
  5. Return list.
    6. -
-
- -
-

14.5.12 Static Semantics: PrototypePropertyNameList

-
ClassElementList : ClassElement
-
    -
  1. If PropName of ClassElement is empty, return a new empty List.
    2. -
  2. If IsStatic of ClassElement is true, return a new empty List.
    3. -
  3. Return a List containing PropName of ClassElement.
    4. -
-
ClassElementList : ClassElementList ClassElement
-
    -
  1. Let list be PrototypePropertyNameList of ClassElementList.
    2. -
  2. If PropName of ClassElement is empty, return list.
    3. -
  3. If IsStatic of ClassElement is true, return list.
    4. -
  4. Append PropName of ClassElement to the end of list.
    5. -
  5. Return list.
    6. -
-
- -
-

14.5.13 Static Semantics: PropName

- -

See also: 12.2.5.6, 14.3.5, 14.4.10

- -
ClassElement : ;
-
    -
  1. Return empty.
    2. -
-
- -
-

14.5.14 Static Semantics: StaticPropertyNameList

-
ClassElementList : ClassElement
-
    -
  1. If PropName of ClassElement is empty, return a new empty List.
    2. -
  2. If IsStatic of ClassElement is false, return a new empty List.
    3. -
  3. Return a List containing PropName of ClassElement.
    4. -
-
ClassElementList : ClassElementList ClassElement
-
    -
  1. Let list be StaticPropertyNameList of ClassElementList.
    2. -
  2. If PropName of ClassElement is empty, return list.
    3. -
  3. If IsStatic of ClassElement is false, return list.
    4. -
  4. Append PropName of ClassElement to the end of list.
    5. -
  5. Return list.
    6. -
-
- -
-

14.5.15 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 15.1.5, 15.2.0.13.

- -

ClassDeclaration : class BindingIdentifier ClassTail

- -
    -
  1. Return an empty List.
    2. -
-
- -
-

14.5.16 Runtime Semantics: ClassDefinitionEvaluation

- -

With parameter className.

- -
ClassTail : ClassHeritageopt { ClassBodyopt }
-
    -
  1. If ClassHeritageopt is not present, then -
      -
    1. Let protoParent be the intrinsic object %ObjectPrototype%.
      2. -
    2. Let constructorParent be the intrinsic object %FunctionPrototype%.
      3. -
    -
    2. -
  2. Else -
      -
    1. Let superclass be the result of evaluating ClassHeritage.
      2. -
    2. ReturnIfAbrupt(superclass).
      3. -
    3. If superclass is null, then -
        -
      1. Let protoParent be null.
        2. -
      2. Let constructorParent be the intrinsic object %FunctionPrototype%.
        3. -
      -
      4. -
    4. Else if IsConstructor(superclass) is false, then throw a - TypeError exception.
      5. -
    5. Else -
        -
      1. Let protoParent be Get(superclass, "prototype").
        2. -
      2. ReturnIfAbrupt(protoParent).
        3. -
      3. If Type(protoParent) is neither Object nor Null, - throw a TypeError exception.
        4. -
      4. Let constructorParent be superclass.
        5. -
      -
      6. -
    -
    3. -
  3. Let proto be ObjectCreate(protoParent).
    4. -
  4. Let lex be the LexicalEnvironment of the running execution context.
    5. -
  5. If className is not undefined, then -
      -
    1. Let scope be NewDeclarativeEnvironment(lex).
      2. -
    2. Let envRec be scope’s environment record.
      3. -
    3. Call the CreateImmutableBinding concrete method of envRec passing className as the argument.
      4. -
    4. Set the running execution context’s LexicalEnvironment to scope.
      5. -
    -
    6. -
  6. If ClassBodyopt is not present, then let constructor be empty.
    7. -
  7. Else, let constructor be ConstructorMethod of ClassBody.
    8. -
  8. If constructor is empty, then -
      -
    1. If ClassHeritageopt is present, then -
        -
      1. Let constructor be the result of parsing the String "constructor(... args){ super - (...args);}" using the syntactic grammar with the goal symbol MethodDefinition.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let constructor be the result of parsing the String "constructor( ){ }" using the - syntactic grammar with the goal symbol MethodDefinition.
        2. -
      -
      3. -
    -
    9. -
  9. Let strict be true.
    10. -
  10. Let constructorInfo be the result of performing DefineMethod for constructor with arguments proto - and constructorParent as the optional functionPrototype argument.
    11. -
  11. Let F be constructorInfo.[[closure]]
    12. -
  12. Perform the abstract operation MakeConstructor with argument F and - false as the optional writablePrototype argument and proto as the optional prototype - argument.
    13. -
  13. Let desc be the PropertyDescriptor{[[Value]]: F, [[Writable]]: true, [[Enumerable]]: - false, [[Configurable]]: true}.
    14. -
  14. Call the [[DefineOwnProperty]] internal method of proto with arguments "constructor" and - desc.
    15. -
  15. If ClassBodyopt is not present, then let methods be a new empty List.
    16. -
  16. Else, let methods be NonConstructorMethodDefinitions of ClassBody.
    17. -
  17. For each MethodDefinition m in order from methods -
      -
    1. If IsStatic of m is false, then -
        -
      1. Let status be the result of performing PropertyDefinitionEvaluation for m with argument - proto.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let status be the result of performing PropertyDefinitionEvaluation for s with argument - F.
        2. -
      -
      3. -
    3. ReturnIfAbrupt(status).
      4. -
    -
    18. -
  18. Set the running execution context’s LexicalEnvironment to lex.
    19. -
  19. If className is not undefined, then -
      -
    1. Call the InitializeBinding concrete method of envRec passing className and F as the - arguments.
      2. -
    -
    20. -
  20. Return F.
    21. -
-
- -
-

14.5.17 Runtime Semantics: Evaluation

-
ClassDeclaration : class BindingIdentifier ClassTail
-
    -
  1. Let className be StringValue(BindingIdentifier).
    2. -
  2. Let value be the result of ClassDefinitionEvaluation of ClassTail with argument className
    3. -
  3. ReturnIfAbrupt(value).
    4. -
  4. Let hasNameProperty be HasOwnProperty(value, - "name").
    5. -
  5. ReturnIfAbrupt(hasNameProperty).
    6. -
  6. If hasNameProperty is false, then -
      -
    1. Perform SetFunctionName(value, className).
      2. -
    -
    7. -
  7. Let env be the running execution context’s LexicalEnvironment.
    8. -
  8. Let status be the result of performing BindingInitialization for BindingIdentifier passing value - and env as the arguments.
    9. -
  9. ReturnIfAbrupt(status).
    10. -
  10. Return NormalCompletion(empty).
    11. -
-
ClassExpression : class BindingIdentifieropt ClassTail
-
    -
  1. If BindingIdentifieropt is not present, then let className be undefined.
    2. -
  2. Else, let className be StringValue(BindingIdentifier).
    3. -
  3. Let value be the result of ClassDefinitionEvaluation of ClassTail with argument className.
    4. -
  4. ReturnIfAbrupt(value).
    5. -
  5. If className is not undefined, then -
      -
    1. Let hasNameProperty be HasOwnProperty(value, - "name").
      2. -
    2. ReturnIfAbrupt(hasNameProperty).
      3. -
    3. If hasNameProperty is false, then -
        -
      1. Perform SetFunctionName(value, className).
        2. -
      -
      4. -
    -
    6. -
  6. Return NormalCompletion(value).
    7. -
-
-
- -
-
-

14.6 Tail - Position Calls

-
- -
-

14.6.1 - Static Semantics: IsInTailPosition(nonterminal) Abstract Operation

- -

The abstract operation IsInTailPosition with argument nonterminal performs the following steps:

- -
    -
  1. Assert: nonterminal is a parsed grammar production.
    2. -
  2. If the source code matching nonterminal is not strict code, then return - false.
    3. -
  3. If nonterminal is not contained within a FunctionBody or ConciseBody, then return - false.
    4. -
  4. Let body be the FunctionBody or ConciseBody that most closely contains nonterminal.
    5. -
  5. If body is the FunctionBody of a GeneratorMethod, GeneratorDeclaration, or a - GeneratorExpression, then return false.
    6. -
  6. Return the result of HasProductionInTailPosition of body with argument nonterminal.
    7. -
- -
-

NOTE Tail Position calls are only defined in strict mode - code because of a common non-standard language extension (see - 9.2.8) that enables observation of the chain of caller contexts.

-
-
- -
-
-

14.6.2 Static Semantics: HasProductionInTailPosition

- -

With parameter nonterminal.

-
- -
-

14.6.2.1 - Statement Rules

-
ConciseBody : AssignmentExpression
-
    -
  1. Return HasProductionInTailPosition of AssignmentExpression with argument nonterminal.
    2. -
-
StatementList : StatementList StatementListItem
-
    -
  1. Let has be HasProductionInTailPosition of StatementList with argument nonterminal.
    2. -
  2. If has is true, then return true.
    3. -
  3. Return HasProductionInTailPosition of StatementListItem with argument nonterminal.
    4. -
- -

FunctionStatementList : [empty]

- -

StatementListItem : Declaration

- -
-
Statement :
-
VariableStatement
-
EmptyStatement
-
ExpressionStatement
-
ContinueStatement
-
BreakStatement
-
ThrowStatement
-
DebuggerStatement
-
Block : { }
-
ReturnStatement : return ;
-
CaseBlock : { }
-
- -
    -
  1. Return false.
    2. -
-
IfStatement : if ( Expression ) Statement else Statement
-
    -
  1. Let has be HasProductionInTailPosition of the first Statement with argument nonterminal.
    2. -
  2. If has is true, then return true.
    3. -
  3. Return HasProductionInTailPosition of the second Statement with argument nonterminal.
    4. -
- -

IfStatement : if ( Expression ) Statement

- -
-
IterationStatement :
-
do Statement while ( Expression ) ;opt
-
while ( Expression ) Statement
-
for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement
-
for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement
-
for ( LexicalDeclaration Expressionopt ; Expressionopt ) Statement
-
for ( LeftHandSideExpression in Expression ) Statement
-
for ( var ForBinding in Expression ) Statement
-
for ( ForDeclaration in Expression ) Statement
-
for ( LeftHandSideExpression of AssignmentExpression ) Statement
-
for ( var ForBinding of AssignmentExpression ) Statement
-
for ( ForDeclaration of AssignmentExpression ) Statement
-
WithStatement : with ( Expression ) Statement
-
- -
-
LabelledStatement :
-
LabelIdentifier : Statement
-
- -
    -
  1. Return HasProductionInTailPosition of Statement with argument nonterminal.
    2. -
-
ReturnStatement : return Expression ;
-
    -
  1. Return HasProductionInTailPosition of Expression with argument nonterminal.
    2. -
-
SwitchStatement : switch ( Expression ) CaseBlock
-
    -
  1. Return HasProductionInTailPosition of CaseBlock with argument nonterminal.
    2. -
-
CaseBlock : { CaseClausesopt DefaultClause CaseClausesopt }
-
    -
  1. Let has be false.
    2. -
  2. If the first CaseClauses is present, let has be HasProductionInTailPosition of the first - CaseClauses with argument nonterminal.
    3. -
  3. If has is true, then return true.
    4. -
  4. Let has be HasProductionInTailPosition of the DefaultClause with argument nonterminal.
    5. -
  5. If has is true, then return true.
    6. -
  6. If the second CaseClauses is present, let has be HasProductionInTailPosition of the second - CaseClauses with argument nonterminal.
    7. -
  7. Return has.
    8. -
-
CaseClauses : CaseClauses CaseClause
-
    -
  1. Let has be HasProductionInTailPosition of CaseClauses with argument nonterminal.
    2. -
  2. If has is true, then return true.
    3. -
  3. Return HasProductionInTailPosition of CaseClause with argument nonterminal.
    4. -
- -

CaseClause : case Expression : StatementListopt

- -
DefaultClause : default : StatementListopt
-
    -
  1. If StatementList is present, return HasProductionInTailPosition of StatementList with argument - nonterminal.
    2. -
  2. Return false.
    3. -
-
TryStatement : try Block Catch
-
    -
  1. Return HasProductionInTailPosition of Catch with argument nonterminal.
    2. -
- -

TryStatement : try Block Finally

- -
TryStatement : try Block Catch Finally
-
    -
  1. Return HasProductionInTailPosition of Finally with argument nonterminal.
    2. -
-
Catch : catch ( CatchParameter ) Block
-
    -
  1. Return HasProductionInTailPosition of Block with argument nonterminal.
    2. -
-
- -
-

14.6.2.2 Expression Rules

- -
-

NOTE A potential tail position call that is immediately followed by return GetValue of the call result is also a possible tail position call. Functional calls cannot - return reference values, so such a GetValue operation will always returns the same value as - the actual function call result.

-
- -
-
AssignmentExpression :
-
YieldExpression
-
ArrowFunction
-
LeftHandSideExpression = AssignmentExpression
-
LeftHandSideExpression AssignmentOperator AssignmentExpression
-
BitwiseANDExpression : BitwiseANDExpression & EqualityExpression
-
BitwiseXORExpression : BitwiseXORExpression ^ BitwiseANDExpression
-
BitwiseORExpression : BitwiseORExpression | BitwiseXORExpression
-
- -
-
EqualityExpression :
-
EqualityExpression == RelationalExpression
-
EqualityExpression != RelationalExpression
-
EqualityExpression === RelationalExpression
-
EqualityExpression !== RelationalExpression
-
- -
-
RelationalExpression :
-
RelationalExpression < ShiftExpression
-
RelationalExpression > ShiftExpression
-
RelationalExpression <= ShiftExpression
-
RelationalExpression >= ShiftExpression
-
RelationalExpression instanceof ShiftExpression
-
RelationalExpression in ShiftExpression
-
- -
-
ShiftExpression :
-
ShiftExpression << AdditiveExpression
-
ShiftExpression >> AdditiveExpression
-
ShiftExpression >>> AdditiveExpression
-
- -
-
AdditiveExpression :
-
AdditiveExpression + MultiplicativeExpression
-
AdditiveExpression - MultiplicativeExpression
-
- -
-
MultiplicativeExpression :
-
MultiplicativeExpression * UnaryExpression
-
MultiplicativeExpression / UnaryExpression
-
MultiplicativeExpression % UnaryExpression
-
- -
-
UnaryExpression :
-
delete UnaryExpression
-
void UnaryExpression
-
typeof UnaryExpression
-
++ UnaryExpression
-
-- UnaryExpression
-
+ UnaryExpression
-
- UnaryExpression
-
~ UnaryExpression
-
! UnaryExpression
-
- -
-
PostfixExpression :
-
LeftHandSideExpression ++
-
LeftHandSideExpression --
-
- -
-
CallExpression :
-
CallExpression [ Expression ]
-
CallExpression . IdentifierName
-
- -
-
MemberExpression :
-
MemberExpression [ Expression ]
-
MemberExpression . IdentifierName
-
super [ Expression ]
-
super . IdentifierName
-
- -
-
PrimaryExpression :
-
this
-
IdentifierReference
-
Literal
-
ArrayInitializer
-
ObjectLiteral
-
FunctionExpression
-
ClassExpression
-
GeneratorExpression
-
GeneratorComprehension
-
RegularExpressionLiteral
-
TemplateLiteral
-
- -
    -
  1. Return false.
    2. -
- -
-
Expression :
-
AssignmentExpression
-
Expression , AssignmentExpression
-
- -
    -
  1. Return HasProductionInTailPosition of AssignmentExpression with argument nonterminal.
    2. -
-
ConditionalExpression : LogicalORExpression ? AssignmentExpression : AssignmentExpression
-
    -
  1. Let has be HasProductionInTailPosition of the first AssignmentExpression with argument - nonterminal.
    2. -
  2. If has is true, then return true.
    3. -
  3. Return HasProductionInTailPosition of the second AssignmentExpression with argument nonterminal.
    4. -
-
LogicalANDExpression : LogicalANDExpression && BitwiseORExpression
-
    -
  1. Return HasProductionInTailPosition of BitwiseORExpression with argument nonterminal.
    2. -
-
LogicalORExpression : LogicalORExpression || LogicalANDExpression
-
    -
  1. Return HasProductionInTailPosition of LogicalANDExpression with argument nonterminal.
    2. -
- -
-
CallExpression :
-
MemberExpression Arguments
-
super Arguments
-
CallExpression Arguments
-
CallExpression TemplateLiteral
-
- -
    -
  1. If this CallExpression is nonterminal, then return true.
    2. -
  2. Return false.
    3. -
- -
-
MemberExpression :
-
MemberExpression TemplateLiteral
-
new super Arguments
-
new MemberExpression Arguments
-
- -
    -
  1. If this MemberExpression is nonterminal, then return true.
    2. -
  2. Return false.
    3. -
- -
-
NewExpression :
-
new NewExpression
-
new super
-
- -
    -
  1. If this NewExpression is nonterminal, then return true.
    2. -
  2. Return false.
    3. -
-
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
-
    -
  1. Let expr be CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
    2. -
  2. Return HasProductionInTailPosition of expr with argument nonterminal.
    3. -
- -
-
ParenthesizedExpression :
-
( Expression )
-
- -
    -
  1. Return HasProductionInTailPosition of Expression with argument nonterminal.
    2. -
-
-
- -
-

14.6.3 - Runtime Semantics: PrepareForTailCall ( )

- -

The abstract operation PrepareForTailCall performs the following steps:

- -
    -
  1. Let leafContext be the running execution context.
    2. -
  2. Suspend leafContext.
    3. -
  3. Pop leafContext from the execution context context stack. The execution context now on the top of the stack becomes the running execution context, however it remains in its suspended state.
    4. -
  4. Assert: leafContext has no further use. It will never be activated as - the running execution context.
    5. -
- -

A tail position call must either release any transient internal resources associated with the currently executing - function execution context before invoking the target function or reuse those - resources in support of the target function.

- -
-

NOTE 1 For example, a tail position call should only grow an implementation’s activation - record stack by the amount that the size of the target function’s activation record exceeds the size of the calling - function’s activation record. If the target function’s activation record is smaller, then the total size of - the stack should decrease.

-
-
-
-
- -
-
-

15 ECMAScript Language: Scripts and Modules

-
- -
-
-

15.1 Scripts

-

Syntax

- -
-
Script :
-
ScriptBodyopt
-
- -
-
ScriptBody :
-
StatementList
-
-
- -
-

15.1.1 Static Semantics: Early Errors

-
ScriptBody : StatementList
-
    -
  • -

    It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate - entries.

    -
    • - -
  • -

    It is a Syntax Error if any element of the LexicallyDeclaredNames - of StatementList also occurs in the VarDeclaredNames of StatementList.

    -
    • - -
  • -

    It is a Syntax Error if StatementList Contains super.

    -
    • -
- -
-

NOTE Additional error conditions relating to conflicting or duplicate declarations are checked - during module linking prior to evaluation of a Script. If any such errors are detected the Script is not - evaluated.

-
-
- -
-

15.1.2 Static Semantics: IsStrict

- -

See also: 14.1.13, 15.2.0.7.

- -
ScriptBody : StatementList
-
    -
  1. If this ScriptBody is contained in strict code or if StatementList - is strict code, then return true. Otherwise, return false.
    2. -
-
- -
-

15.1.3 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.1.14, 14.2.10, 14.4.8, 14.5.10, 15.2.0.10.

- -
ScriptBody : StatementList
-
    -
  1. Return TopLevelLexicallyDeclaredNames of StatementList.
    2. -
- -
-

NOTE At the top level of a Script, function declarations are treated like var - declarations rather than like lexical declarations.

-
-
- -
-

15.1.4 Static Semantics: LexicallyScopedDeclarations

-
ScriptBody : StatementList
-
    -
  1. Return TopLevelLexicallyScopedDeclarations of StatementList.
    2. -
-
- -
-

15.1.5 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.2.0.13.

- -
ScriptBody : StatementList
-
    -
  1. Return TopLevelVarDeclaredNames of StatementList.
    2. -
-
- -
-

15.1.6 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.2.0.14.

- -

.

- -
ScriptBody : StatementList
-
    -
  1. Return TopLevelVarScopedDeclarations of StatementList.
    2. -
-
- -
-

15.1.7 Runtime Semantics: ScriptEvaluation

- -

With argument realm and deletableBindings.

- -
Script : ScriptBodyopt
-
    -
  1. The code of this Script is strict mode code if the Directive Prologue (14.1.1) of its ScriptBody contains a Use Strict Directive or if any of the conditions of - 10.2.1 apply. If the code of this Script is strict mode code, ScriptBody is evaluated in the following steps as strict mode code. Otherwise ScriptBody is evaluated in the following steps as - non-strict mode code.
    2. -
  2. If ScriptBody is not present, return NormalCompletion(empty).
    3. -
  3. Let globalEnv be realm.[[globalEnv]].
    4. -
  4. Let status be GlobalDeclarationInstantiation(ScriptBody, globalEnv, and - deletableBindings).
    5. -
  5. ReturnIfAbrupt(status).
    6. -
  6. Let progCxt be a new ECMAScript code execution context.
    7. -
  7. Set the progCxt’s Realm to realm.
    8. -
  8. Set the progCxt’s VariableEnvironment to globalEnv.
    9. -
  9. Set the progCxt’s LexicalEnvironment to globalEnv.
    10. -
  10. If there is a currently running execution context, suspend it.
    11. -
  11. Push progCxt on to the execution context stack; progCxt is now the running execution context.
    12. -
  12. Let result be the result of evaluating ScriptBody.
    13. -
  13. Suspend progCxt and remove it from the - execution context stack.
    14. -
  14. If the execution context stack is not empty, resume the context that is now on - the top of the execution context stack as the - running execution context. Otherwise, the execution context stack is now - empty and there is no running execution context.
    15. -
  15. Return result.
    16. -
- -
-

NOTE The processes for initiating the evaluation of a Script and for dealing with the - result of such an evaluation are defined by an ECMAScript implementation and not by this specification.

-
-
- -
-

15.1.8 Runtime Semantics: GlobalDeclarationInstantiation

- -
-

NOTE When an execution context is established for - evaluating scripts, declarations are instantiated in the current global environment. Each global binding declared in the - code is instantiated.

-
- -

GlobalDeclarationInstantiation is performed as follows using arguments script, env, and deletableBindings. script is the ScriptBody that for which - the execution context is being established. env is the global environment record in which bindings are to be created. - deletableBindings is true if the bindings that are created should be deletable.

- -
    -
  1. Let strict be IsStrict of script.
    2. -
  2. Let lexNames be the LexicallyDeclaredNames of script.
    3. -
  3. Let varNames be the VarDeclaredNames of script.
    4. -
  4. For each name in lexNames, do -
      -
    1. If the result of calling env’s HasVarDeclaration concrete method - passing name as the argument is true, throw a SyntaxError exception.
      2. -
    2. If the result of calling env’s HasLexicalDeclaration - concrete method passing name as the argument is true, throw a SyntaxError exception.
      3. -
    -
    5. -
  5. For each name in varNames, do -
      -
    1. If the result of calling env’s HasLexicalDeclaration - concrete method passing name as the argument is true, throw a SyntaxError exception.
      2. -
    -
    6. -
  6. Let varDeclarations be the VarScopedDeclarations of script.
    7. -
  7. Let functionsToInitialize be an empty List.
    8. -
  8. Let declaredFunctionNames be an empty List.
    9. -
  9. For each d in varDeclarations, in reverse list order do -
      -
    1. If d is neither a VariableDeclaration or a ForBinding, then -
        -
      1. Assert: d is either a FunctionDeclaration or a - GeneratorDeclaration.
        2. -
      2. NOTE If there are multiple FunctionDeclarations - for the same name, the last declaration is used.
        3. -
      3. Let fn be the sole element of the BoundNames of d.
        4. -
      4. If fn is not an element of declaredFunctionNames, then -
          -
        1. Let fnDefinable be the result of calling env’s CanDeclareGlobalFunction concrete method passing fn as the - argument.
          2. -
        2. If fnDefinable is false, throw TypeError exception.
          3. -
        3. Append fn to declaredFunctionNames.
          4. -
        4. Insert d as the first element of functionsToInitialize.
          5. -
        -
        5. -
      -
      2. -
    -
    10. -
  10. Let declaredVarNames be an empty List.
    11. -
  11. For each d in varDeclarations, do -
      -
    1. If d is a VariableDeclaration or a ForBinding then -
        -
      1. For each String vn in the BoundNames of d, do -
          -
        1. If vn is not an element of declaredFunctionNames, then -
            -
          1. Let vnDefinable be the result of calling env’s CanDeclareGlobalVar concrete method passing vn as the - argument.
            2. -
          2. If vnDefinable is false, throw TypeError exception.
            3. -
          3. If vn is not an element of declaredVarNames, then -
              -
            1. Append vn to declaredVarNames.
              2. -
            -
            4. -
          -
          2. -
        -
        2. -
      -
      2. -
    -
    12. -
  12. NOTE: No abnormal terminations occur after this algorithm step.
    13. -
  13. For each FunctionDeclaration f in functionsToInitialize, do -
      -
    1. Let fn be the sole element of the BoundNames of f.
      2. -
    2. Let fo be the result of performing InstantiateFunctionObject for f with argument env.
      3. -
    3. Let status be the result of calling env’s CreateGlobalFunctionBinding concrete method passing fn, - fo, and deletableBindings as the arguments.
      4. -
    4. ReturnIfAbrupt(status).
      5. -
    -
    14. -
  14. For each String vn in declaredVarNames, in list order do -
      -
    1. Let status be the result of calling env’s CreateGlobalVarBinding concrete method passing vn and - deletableBindings as the argument.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    15. -
  15. Let lexDeclarations be the LexicallyScopedDeclarations of script.
    16. -
  16. For each element d in lexDeclarations do -
      -
    1. NOTE Except for generator function declarations, lexically declarated names are only instantiated here but not - initialized.
      2. -
    2. For each element dn of the BoundNames of d do -
        -
      1. If IsConstantDeclaration of d is true, then -
          -
        1. Let status be the result of calling env’s CreateImmutableBinding concrete method - passing dn as the argument.
          2. -
        -
        2. -
      2. Else, -
          -
        1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - dn and false as the arguments.
          2. -
        -
        3. -
      3. Assert: status is never an abrupt completion for lexically declared names.
        4. -
      -
      3. -
    3. If d is a GeneratorDeclaration production, then -
        -
      1. Let fn be the sole element of the BoundNames of d.
        2. -
      2. Let fo be the result of performing InstantiateFunctionObject for d with argument - env.
        3. -
      3. Let status be the result of calling env’s SetMutableBinding concrete method passing - fn, fo, and false as the arguments.
        4. -
      4. ReturnIfAbrupt(status).
        5. -
      -
      4. -
    -
    17. -
  17. Return NormalCompletion(empty)
    18. -
- -
-

NOTE Early errors specified in 15.1.1 - prevent name conflicts between function/var declarations and let/const/class declarations as well as redeclaration of - let/const/class bindings for declaration contained within a single Script. However, such conflicts and - redeclarations that span more than one Script are detected as runtime errors during GlobalDeclarationInstantiation. - If any such errors are detected, no bindings are instantiated for the script.

- -

Unlike explicit var or function declarations, properties that are directly created on the global object result in - global bindings that may be shadowed by let/const/class declarations.

-
-
- -
-

15.1.9 - Runtime Semantics: ScriptEvaluationTask ( source )

- -

The task ScriptEvaluationTask with parameter source parses, validates, and evaluates the Script represented by source.

- -
    -
  1. Assert: source is a SourceCharacter sequence (see 10).
    2. -
  2. Parse source using Script as the goal symbol and analyze the parse result for any Early Error - conditions. If the parse was successful and no ealy errors were found, then let script the resulting parse - tree. Otherwise, let script be an indication of one or more parsing errors and/or early errors. Parsing and - early error detection may be interweaved in an implementation dependent manner. If more than one parse or early error - is present, the number and ordering of reported errors is implementation dependent but at least one error must be - reported.
    3. -
  3. If script is an error indication, then -
      -
    1. Report or log the error(s) in an implementation dependent manner.
      2. -
    2. Let status be NormalCompletion(undefined).
      3. -
    -
    4. -
  4. Else, -
      -
    1. Let realm be the running execution context’s Realm.
      2. -
    2. Let status be the result of ScriptEvaluation of script with arguments realm and - false.
      3. -
    -
    5. -
  5. NextTask status.
    6. -
- -
-

NOTE An implementation may parse a Script and analyze it for Early Error conditions - prior to the execution of the ScriptEvaluationTask for that Script. However, the reporting of any errors must be - deferred until the ScriptEvaluationTask is actually exeuted.

-
-
-
- -
-
-

15.2 Modules

-

Syntax

- -
-
Module :
-
ModuleBodyopt
-
- -
-
ModuleBody :
-
ModuleItemList
-
- -
-
ModuleItemList :
-
ModuleItem
-
ModuleItemList ModuleItem
-
- -
-
ModuleItem :
-
ImportDeclaration
-
ExportDeclaration
-
StatementListItem
-
-
- -
-
-

15.2.0 Module Static Semantics

-
- -
-

15.2.0.1 Static Semantics: Early Errors

-
ModuleBody : ModuleItemList
-
    -
  • -

    It is a Syntax Error if the LexicallyDeclaredNames of ModuleItemList contains any duplicate - entries.

    -
    • - -
  • -

    It is a Syntax Error if the ExportedBindings of ModuleItemList contains any duplicate - entries.

    -
    • - -
  • -

    It is a Syntax Error if any element of the LexicallyDeclaredNames of ModuleItemList also - occurs in the VarDeclaredNames of ModuleItemList.

    -
    • - -
  • -

    It is a Syntax Error if ModuleItemList Contains super.

    -
    • -
- -
-

NOTE Additional error conditions relating to conflicting or duplicate declarations are - checked during module linking prior to evaluation of a Module. If any such errors are detected the Module - is not evaluated.

-
-
- -
-

15.2.0.2 Static Semantics: DeclaredNames

-
Module : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
Module : ModuleBody
-
    -
  1. Let names be LexicallyDeclaredNames of ModuleBody.
    2. -
  2. Append to names the elements of the VarDeclaratedNames of ModuleBody.
    3. -
  3. Return names.
    4. -
-
- -
-

15.2.0.3 Static Semantics: ExportedBindings

- -

See also:15.2.2.2.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let names be ExportedBindings of ModuleItemList.
    2. -
  2. Append to names the elements of the ExportedBindings of ModuleItem.
    3. -
  3. Return names.
    4. -
- -
-
ModuleItem :
-
ImportDeclaration
-
StatementListItem
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

15.2.0.4 Static Semantics: ExportEntries

- -

See also:15.2.2.3.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let entries be ExportEntries of ModuleItemList.
    2. -
  2. Append to entries the elements of the ExportEntries of ModuleItem.
    3. -
  3. Return entries.
    4. -
- -
-
ModuleItem :
-
ImportDeclaration
-
StatementListItem
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

15.2.0.5 Static Semantics: ImportedBindings

-
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let names be ImportedBindings of ModuleItemList.
    2. -
  2. Append to names the elements of the ImportedBindings of ModuleItem.
    3. -
  3. Return names.
    4. -
-
ModuleItem : ImportDeclaration
-
    -
  1. Return the BoundNames of ImportDeclaration.
    2. -
- -
-
ModuleItem :
-
ExportDeclaration
-
StatementListItem
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

15.2.0.6 Static Semantics: ImportEntries

- -

See also:15.2.1.3.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let entries be ImportEntries of ModuleItemList.
    2. -
  2. Append to entries the elements of the ImportEntries of ModuleItem.
    3. -
  3. Return entries.
    4. -
- -
-
ModuleItem :
-
ExportDeclaration
-
StatementListItem
-
- -
    -
  1. Return a new empty List.
    2. -
-
- -
-

15.2.0.7 Static Semantics: IsStrict

- -

See also: 14.1.13, 15.1.2.

- -
ModuleBody : ModuleItemList
-
    -
  1. Return true.
    2. -
-
- -
-

15.2.0.8 Static Semantics: KnownExportEntries

-
ModuleBody : ModuleItemList
-
    -
  1. Let allExports be ExportEntries of ModuleItemList.
    2. -
  2. Return a new List containing all the entries of - allEntries whose [[ImportName]] field is not all.
    3. -
-
- -
-

15.2.0.9 Static Semantics: ModuleRequests

- -

See also: 15.2.1.5, 15.2.2.5.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItem
-
    -
  1. Return ModuleRequests of ModuleItem.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let moduleNames be ModuleRequests of ModuleItemList.
    2. -
  2. Let additionalNames be ModuleRequests of ModuleItem.
    3. -
  3. Append to moduleNames each element of additionalNames that is not already an element of - moduleNames.
    4. -
  4. Return moduleNames.
    5. -
-
ModuleItem : StatementListItem
-
    -
  1. Return a new empty List.
    2. -
-
- -
-

15.2.0.10 Static Semantics: LexicallyDeclaredNames

- -

See also: 13.1.3, 13.11.3, 14.1.14, 14.2.10, 14.4.8, 14.5.10, 15.1.3.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let names be LexicallyDeclaredNames of ModuleItemList.
    2. -
  2. Append to names the elements of the LexicallyDeclaredNames of ModuleItem.
    3. -
  3. Return names.
    4. -
-
ModuleItem : ImportDeclaration
-
    -
  1. Return the BoundNames of ImportDeclaration.
    2. -
-
ModuleItem : ExportDeclaration
-
    -
  1. If ExportDeclaration is export VariableStatement; then return a new empty List.
    2. -
  2. Return the BoundNames of ExportDeclaration.
    3. -
-
ModuleItem : StatementListItem
-
    -
  1. Return LexicallyDeclaredNames of StatementListItem.
    2. -
- -
-

NOTE At the top level of a Module, function declarations are treated like lexical - declarations rather than like var declarations.

-
-
- -
-

15.2.0.11 Static Semantics: LexicallyScopedDeclarations

- -

See also: 13.1.2, 13.11.2.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let declarations be LexicallyScopedDeclarations of ModuleItemList.
    2. -
  2. Append to declarations the elements of the LexicallyScopedDeclarations of ModuleItem.
    3. -
  3. Return declarations.
    4. -
-
ModuleItem : ImportDeclaration
-
    -
  1. If the BoundNames of ImportDeclarations is empty, then return an empty List.
    2. -
  2. Return a new List containing ImportDeclaration.
    3. -
-
ModuleItem : ExportDeclaration
-
    -
  1. If ExportDeclaration is export Declaration; then return a new List containing Declaration.
    2. -
  2. Return a new empty List.
    3. -
-
- -
-

15.2.0.12 Static Semantics: UnknownExportEntries

-
ModuleBody : ModuleItemList
-
    -
  1. Let allExports be ExportEntries of ModuleItemList.
    2. -
  2. Return a new List containing all the entries of - allEntries whose [[ImportName]] field is all.
    3. -
-
- -
-

15.2.0.13 Static Semantics: VarDeclaredNames

- -

See also: 13.0.1, 13.1.8, 13.2.2.2, 13.5.1, 13.6.1.1, 13.6.2.1, 13.6.3.1, 13.6.4.3, 13.10.2, 13.11.4, 13.12.2, 13.14.2, 14.1.16, 14.4.12, 14.5.15, 15.1.5.

- -
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let names be VarDeclaredNames of ModuleItemList.
    2. -
  2. Append to names the elements of the VarDeclaredNames of ModuleItem.
    3. -
  3. Return names.
    4. -
-
ModuleItem : ImportDeclaration
-
    -
  1. Return an empty List.
    2. -
-
ModuleItem : ExportDeclaration
-
    -
  1. If ExportDeclaration is export VariableStatement; then return BoundNames of - ExportDeclaration.
    2. -
  2. Return a new empty List.
    3. -
-
- -
-

15.2.0.14 Static Semantics: VarScopedDeclarations

- -

See also: 13.0.2, 13.1.9, 13.2.2.3, 13.5.2, 13.6.1.2, 13.6.2.2, 13.6.3.2, 13.6.4.4, 13.10.3, 13.11.5, 13.12.4, 13.14.3, 14.1.18, 14.2.14, 14.4.13, 15.1.6.

- -

.

- -
ModuleItemList : [empty]
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItemList : ModuleItemList ModuleItem
-
    -
  1. Let declarations be VarScopedDeclarations of ModuleItemList.
    2. -
  2. Append to declarations the elements of the VarScopedDeclarations of ModuleItem.
    3. -
  3. Return declarations.
    4. -
-
ModuleItem : ImportDeclaration
-
    -
  1. Return a new empty List.
    2. -
-
ModuleItem : ExportDeclaration
-
    -
  1. If ExportDeclaration is export VariableStatement; then return - VarScopedDeclarations of VariableStatement.
    2. -
  2. Return a new empty List.
    3. -
-
- -
-

15.2.0.15 Runtime Semantics: ModuleDeclarationInstantiation( code, env )

- -

TO DO

- -
    -
  1. Let declarations be the LexicallyScopedDeclarations of code.
    2. -
  2. Let functionsToInitialize be an empty List.
    3. -
  3. For each element d in declarations do -
      -
    1. For each element dn of the BoundNames of d do -
        -
      1. If IsConstantDeclaration of d is true, then -
          -
        1. Call env’s CreateImmutableBinding concrete method passing dn as the argument.
          2. -
        -
        2. -
      2. Else, -
          -
        1. Let status be the result of calling env’s CreateMutableBinding concrete method - passing dn and false as the arguments.
          2. -
        2. Assert: status is never an abrupt completion.
          3. -
        -
        3. -
      -
      2. -
    2. If d is a GeneratorDeclaration production or a FunctionDeclaration production, then -
        -
      1. Append d to functionsToInitialize.
        2. -
      -
      3. -
    -
    4. -
  4. For each production f in functionsToInitialize, in list order do -
      -
    1. Let fn be the sole element of the BoundNames of f.
      2. -
    2. Let fo be the result of performing InstantiateFunctionObject for f with argument - env.
      3. -
    3. Call env’s InitializeBinding concrete method passing fn, and fo as the - arguments.
      4. -
    -
    5. -
-
-
- -
-
-

15.2.1 - Imports

-

Syntax

- -
-
ImportDeclaration :
-
ModuleImport
-
import ImportClause FromClause ;
-
import ModuleSpecifier ;
-
- -
-
ModuleImport :
-
module [no LineTerminator here] ImportedBinding FromClause ;
-
- -
-
FromClause :
-
from ModuleSpecifier
-
- -
-
ImportClause :
-
ImportedBinding
-
ImportedBinding , NamedImports
-
NamedImports
-
- -
-
NamedImports :
-
{ }
-
{ ImportsList }
-
{ ImportsList , }
-
- -
-
ImportsList :
-
ImportSpecifier
-
ImportsList , ImportSpecifier
-
- -
-
ImportSpecifier :
-
ImportedBinding
-
IdentifierName as ImportedBinding
-
- -
-
ModuleSpecifier :
-
StringLiteral
-
- -
-
ImportedBinding :
-
BindingIdentifier
-
-
- -
-

15.2.1.1 Static Semantics: Early Errors

-
ModuleItem : ImportDeclaration
-
    -
  • -

    It is a Syntax Error if the BoundNames of ImportDeclaration contains any duplicate - entries.

    -
    • -
-
- -
-

15.2.1.2 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.1.

- -
ImportDeclaration : import ImportClause FromClause ;
-
    -
  1. Return the BoundNames of ImportClause.
    2. -
-
ImportDeclaration : import ModuleSpecifier ;
-
    -
  1. Return a new empty List.
    2. -
-
ModuleImport : module ImportedBinding FromClause ;
-
    -
  1. Return the BoundNames of ImportedBinding.
    2. -
-
ImportClause : ImportedBinding , NamedImports
-
    -
  1. Let names be the BoundNames of ImportedBinding.
    2. -
  2. Append to names the elements of the BoundNames of NamedImports.
    3. -
  3. Return names.
    4. -
-
NamedImports : { }
-
    -
  1. Return a new empty List.
    2. -
-
ImportsList : ImportsList , ImportSpecifier
-
    -
  1. Let names be the BoundNames of ImportsList.
    2. -
  2. Append to names the elements of the BoundNames of ImportSpecifier.
    3. -
  3. Return names.
    4. -
-
ImportSpecifier : IdentifierName as ImportedBinding
-
    -
  1. Return the BoundNames of ImportedBinding.
    2. -
-
- -
-

15.2.1.3 Static Semantics: ImportEntries

- -

See also:15.2.0.6.

- -
ImportDeclaration : import ImportClause FromClause ;
-
    -
  1. Let module be the sole element of ModuleRequests of FromClause.
    2. -
  2. Return ImportEntriesForModule of ImportClause with argument module.
    3. -
-
ImportDeclaration : import ModuleSpecifier ;
-
    -
  1. Return a new empty List.
    2. -
-
ModuleImport : module ImportedBinding FromClause ;
-
    -
  1. Let module be ModuleRequests of FromClause.
    2. -
  2. Let localName be the StringValue of ImportedBinding.
    3. -
  3. Let entry be the Record {[[ModuleRequest]]: module, [[ImportName]]: "default", - [[LocalName]]: localName }.
    4. -
  4. Return a new List containing entry.
    5. -
-
- -
-

15.2.1.4 Static Semantics: ImportEntriesForModule

- -

With parameter module.

- -
ImportClause : ImportedBinding , NamedImports
-
    -
  1. Let localName be the StringValue of ImportedBinding.
    2. -
  2. Let defaultEntry be the Record {[[ModuleRequest]]: module, [[ImportName]]: "default", - [[LocalName]]: localName }.
    3. -
  3. Return a new List containing defaultEntry.
    4. -
-
ImportClause : ImportedBinding , NamedImports
-
    -
  1. Let localName be the StringValue of ImportedBinding.
    2. -
  2. Let defaultEntry be the Record {[[ModuleRequest]]: module, [[ImportName]]: "default", - [[LocalName]]: localName }.
    3. -
  3. Let entries be a new List containing - defaultEntry.
    4. -
  4. Append to entries the elements of the ImportEntriesForModule of NamedImports with argument - module.
    5. -
  5. Return entries.
    6. -
-
NamedImports : { }
-
    -
  1. Return a new empty List.
    2. -
-
ImportsList : ImportsList , ImportSpecifier
-
    -
  1. Let specs be the ImportEntriesForModule of ImportsList with argument module.
    2. -
  2. Append to specs the elements of the ImportEntriesForModule of ImportSpecifier with argument - module.
    3. -
  3. Return specs.
    4. -
-
ImportSpecifier : ImportedBinding
-
    -
  1. Let localName be the StringValue of ImportedBinding.
    2. -
  2. Let entry be the Record {[[ModuleRequest]]: module, [[ImportName]]: localName , [[LocalName]]: - localName }.
    3. -
  3. Return a new List containing entry.
    4. -
-
ImportSpecifier : IdentifierName as ImportedBinding
-
    -
  1. Let importName be the StringValue of IdentifierName.
    2. -
  2. Let localName be the StringValue of ImportedBinding.
    3. -
  3. Let entry be the Record {[[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: - localName }.
    4. -
  4. Return a new List containing entry.
    5. -
-
- -
-

15.2.1.5 Static Semantics: ModuleRequests

- -

See also: 15.2.0.9, 15.2.2.5.

- -
ImportDeclaration : import ImportClause FromClause ;
-
    -
  1. Return ModuleRequests of FromClause.
    2. -
-
ModuleImport : module ImportedBinding FromClause ;
-
    -
  1. Return ModuleRequests of FromClause.
    2. -
-
ModuleSpecifier : StringLiteral
-
    -
  1. Return a List containing the StringValue of - StringLiteral.
    2. -
-
- -
-

15.2.1.6 Runtime Semantics: Module Objects

-
ModuleImport : module ImportedBinding FromClause ;
- -

An ModuleImport imports a module and introduces a single binding within the containing module - environment. The value of such a binding as a Module object.

- -

A Module object is an exotic object whose own properties corresponding corresponding to the ExportedBindings of the - module identifed by the ModuleImport FromClause. Each property name is - the StringValue of the corresponding exported binding. These are the only properties of an Module object. Each one is a - read-only property with attributes {[[Configurable]]: false, [[Enumerable]]: true}. Module objects are not extensible.

- -

TO DO

- -

Needs to decide whether a module object is an ordinary or an exotic object. Whether - properties are accessor or defined via [[Get]], etc.

-
-
- -
-
-

15.2.2 - Exports

-

Syntax

- -
-
ExportDeclaration :
-
export * FromClause ;
-
export ExportClause[NoReference] FromClause ;
-
export ExportClause ;
-
export VariableStatement
-
export Declaration[Default]
-
export default AssignmentExpression[In] ;
-
- -
-
ExportClause[NoReference] :
-
{ }
-
{ ExportsList[?NoReference] }
-
{ ExportsList[?NoReference] , }
-
- -
-
ExportsList[NoReference] :
-
ExportSpecifier[?NoReference]
-
ExportsList[?NoReference] , ExportSpecifier[?NoReference]
-
- -
-
ExportSpecifier[NoReference] :
-
[~NoReference] IdentifierReference
-
[~NoReference] IdentifierReference as IdentifierName
-
[+NoReference] IdentifierName
-
[+NoReference] IdentifierName as IdentifierName
-
- -
-

NOTE ExportSpecifier is used to export bindings from the enclosing module - Module. ExportSpecifier[NoReference] is used to export bindings from a referenced Module. In that case - IdentifierReference restrictions are not applied to the naming of the items to be exported because they are not - used to create local bindings.

-
-
- -
-

15.2.2.1 Static Semantics: BoundNames

- -

See also: 13.2.1.2, 13.2.2.1, 12.1.2, 13.6.4.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.1.2.

- -
-
ExportDeclaration :
-
export * FromClause ;
-
export ExportClause FromClause ;
-
export ExportClause ;
-
- -
    -
  1. Return a new empty List.
    2. -
- -

ExportDeclaration : export VariableStatement ;

- -
    -
  1. Return the BoundNames of VariableStatement.
    2. -
- -

ExportDeclaration : export Declaration;

- -
    -
  1. Return the BoundNames of Declaration.
    2. -
- -

ExportDeclaration : export default AssignmentExpression;

- -
    -
  1. Return a List containing "default".
    2. -
-
- -
-

15.2.2.2 Static Semantics: ExportedBindings

- -

See also:15.2.0.2.

- -
ExportDeclaration : export * FromClause ;
-
    -
  1. Return a new empty List.
    2. -
- -
-
ExportDeclaration :
-
export ExportClause FromClause ;
-
export ExportClause ;
-
- -
    -
  1. Return the ExportedBindings of this ExportClause.
    2. -
- -
-
ExportDeclaration :
-
export VariableStatement
-
export Declaration[Default]
-
- -
    -
  1. Return the BoundNames of this ExportDeclaration.
    2. -
- -

ExportDeclaration : export default AssignmentExpression;

- -
    -
  1. Return a List containing "default".
    2. -
-
ExportClause : { }
-
    -
  1. Return a new empty List.
    2. -
-
ExportsList : ExportsList , ExportSpecifier
-
    -
  1. Let names be the ExportedBindings of ExportsList.
    2. -
  2. Append to names the elements of the ExportedBindings of ExportSpecifier.
    3. -
  3. Return names.
    4. -
-
ExportSpecifier : IdentifierReference
-
    -
  1. Return a List containing the StringValue of - IdentifierReference.
    2. -
-
ExportSpecifier : IdentifierReference as IdentifierName
-
    -
  1. Return a List containing the StringValue of - IdentifierName.
    2. -
-
ExportSpecifier : IdentifierName
-
    -
  1. Return a List containing the StringValue of - IdentifierName.
    2. -
-
ExportSpecifier : IdentifierName as IdentifierName
-
    -
  1. Return a List containing the StringValue of the second - IdentifierName.
    2. -
-
- -
-

15.2.2.3 Static Semantics: ExportEntries

- -

See also:15.2.0.4.

- -
ExportDeclaration : export * FromClause ;
-
    -
  1. Let module be the sole element of ModuleRequests of FromClause.
    2. -
  2. Let entry be the Record {[[ModuleRequest]]: module, [[ImportName]]: all, [[LocalName]]: null, [[ExportName]]: null }.
    3. -
  3. Return a new List containing entry.
    4. -
-
ExportDeclaration : export ExportClause FromClause ;
-
    -
  1. Let module be the sole element of ModuleRequests of FromClause.
    2. -
  2. Return ExportEntriesForModule of ExportClause with argument module.
    3. -
-
ExportDeclaration : export ExportClause ;
-
    -
  1. Return ExportEntriesForModule of ExportClause with argument null.
    2. -
-
ExportDeclaration : export VariableStatement ;
-
    -
  1. Let entries be a new empty List.
    2. -
  2. Let names be the BoundNames of VariableStatement.
    3. -
  3. Repeat for each name in names, -
      -
    1. Append to entries the Record {[[ModuleRequest]]: null, [[ImportName]]: null, [[LocalName]]: - name, [[ExportName]]: name }.
      2. -
    -
    4. -
  4. Return entries.
    5. -
-
ExportDeclaration : export Declaration ;
-
    -
  1. Let entries be a new empty List.
    2. -
  2. Let names be the BoundNames of Declaration.
    3. -
  3. Repeat for each name in names, -
      -
    1. Append to entries the Record {[[ModuleRequest]]: null, [[ImportName]]: null, [[LocalName]]: - name, [[ExportName]]: name }.
      2. -
    -
    4. -
  4. Return entries.
    5. -
- -

ExportDeclaration : export default AssignmentExpression;

- -
    -
  1. Let entry be the Record {[[ModuleRequest]]: null, [[ImportName]]: null, [[LocalName]]: - "default", [[ExportName]]: "default"}.
    2. -
  2. Return a new List containing entry.
    3. -
-
- -
-

15.2.2.4 Static Semantics: ExportEntriesForModule

- -

With parameter module.

- -
ExportClause : { }
-
    -
  1. Return a new empty List.
    2. -
-
ExportsList : ExportsList , ExportSpecifier
-
    -
  1. Let specs be the ExportEntriesForModule of ExportsList with argument module.
    2. -
  2. Append to specs the elements of the ExportEntriesForModule of ExportSpecifier with argument - module.
    3. -
  3. Return specs.
    4. -
-
ExportSpecifier : IdentifierReference
-
    -
  1. Let localName be the StringValue of IdentifierReference.
    2. -
  2. Return a new List containing the Record {[[ModuleRequest]]: - module, [[ImportName]]: null, [[LocalName]]: localName, [[ExportName]]: localName - }.
    3. -
-
ExportSpecifier : IdentifierReference as IdentifierName
-
    -
  1. Let localName be the StringValue of IdentifierReference.
    2. -
  2. Let exportName be the StringValue of IdentifierName.
    3. -
  3. Return a new List containing the Record {[[ModuleRequest]]: - module, [[ImportName]]: null, [[LocalName]]: localName, [[ExportName]]: exportName - }.
    4. -
-
ExportSpecifier : IdentifierName
-
    -
  1. Let sourceName be the StringValue of IdentifierName.
    2. -
  2. Return a new List containing the Record {[[ModuleRequest]]: - module, [[ImportName]]: sourceName, [[LocalName]]: null, [[ExportName]]: sourceName - }.
    3. -
-
ExportSpecifier : IdentifierName as IdentifierName
-
    -
  1. Let sourceName be the StringValue of the first IdentifierName.
    2. -
  2. Let exportName be the StringValue of the second IdentifierName.
    3. -
  3. Return a new List containing the Record {[[ModuleRequest]]: - module, [[ImportName]]: sourceName, [[LocalName]]: null, [[ExportName]]: exportName - }.
    4. -
-
- -
-

15.2.2.5 Static Semantics: ModuleRequests

- -

See also: 15.2.0.9, 15.2.1.5.

- -
ExportDeclaration : export ExportClause FromClause ;
-
    -
  1. Return the ModuleRequests of FromClause.
    2. -
- -
-
ExportDeclaration :
-
export ExportClause ;
-
export VariableStatement
-
export Declaration
-
export default AssignmentExpression ;
-
- -
    -
  1. Return a new empty List.
    2. -
-
-
- -
-
-

15.2.3 Runtime Semantics: Loader State

-
- -
-
-

15.2.3.1 Loader Records and Loader Objects

- -

Loader Records contain the state of a of distinct module loading context. Each Loader Record has the fields defined - in Table 34. Loader objects (26.3) are ECMAScript objects that - permit ECMAScript code to define and manage module loading contexts.

- -
-
Table 34 — Loader Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValue TypeMeaning
[[Realm]]Realm RecordThe Realm associated with the loader. All scripts and modules evaluated by this loader run in the scope of the global object associated with this Realm.
[[Modules]] -

List of

- -

Record {[[Name]], [[Module]]} where [[Name]] is a String and [[Module]] is a Module Record

- 		Normalized names bound to fully linked Module records. The list can contain modules whose code has not yet been evaluated. However, except for the case of cyclic imports, such modules are not exposed to user code.
[[Loads]]List of Load RecordOutstanding asynchronous module load requests that have been made to this loader.
[[LoaderObj]Object or UndefinedThe Loader object (26.3) that reflects this Loader Record.
-
-
- -
-

15.2.3.1.1 CreateLoaderRecord(realm, object) Abstract Operation

- -

The abstract operation CreateLoaderRecord creates and returns a new Loader Record. The argument realm is - the Realm record that will be associated with Loader. The argument object is - the either undefined or the Loader object that will reflect this Loader record.

- -

The following steps are taken:

- -
    -
  1. Let loader be a new Loader Record.
    2. -
  2. Set loader.[[Realm]] to realm.
    3. -
  3. Set loader.[[Modules]] to a new empty List.
    4. -
  4. Set loader.[[Loads]] to a new empty List.
    5. -
  5. Set loader.[[LoaderObj]] to object.
    6. -
  6. Return loader.
    7. -
-
-
- -
-
-

15.2.3.2 Load Records and LoadRequest Objects

- -

The Load Record represents an attempt to locate, fetch, translate, and parse a single module.

- -

Each Load Record has the fields defined in Table 35:

- -
-
Table 35 — Load Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValue TypeMeaning
[[Status]]One of: "loading", "loaded", "linked", "failed".The current state of this Load request.
[[Name]]String | undefinedThe normalized name of the module being loaded, or undefined if loading an anonymous module.
[[LinkSets]]List of LinkSet RecordA List of all LinkSets that require this Load request to succeed. There is a many-to-many relation between Load records and LinkSets. A single import() call can have a large dependency tree, involving many Load records. Many import() calls, if they depend on the same module, can be waiting for a single Load to complete.
[[Metadata]]ObjectAn object passed to each loader hook which hooks may use for any purpose.
[[Address]]Object | undefinedThe result of the locate hook.
[[Source]]String | undefinedThe result of the translate hook.
[[Kind]]One of: undefined, dynamic, declarativeOnce the Load reaches the "loaded" state, either declarative or dynamic. If the instantiate hook returned undefined, the module is declarative, and load.[[Body]] contains a Module parse. Otherwise, the instantiate hook returned a ModuleFactory object and [[Execute]] contains the .execute callable object.
[[Body]]undefined or a parse resultIf [[Kind]] is declarative, the parse of a Module production. Otherwise undefined.
[[Execute]]If [[Kind]] is dynamic, the value of factory.execute. Otherwise undefined.
[[Dependencies]]Undefined or List of RecordsIf [[Status]] is not "loading", a List of pairs. Each pair consists of two strings: a module name as it appears in a module, import, or export from declaration in load.[[Body]], and the corresponding normalized module name.
[[Exception]]If [[Status]] is "failed", the exception value that was thrown, causing the load to fail. Otherwise, null.
[[Module]]The Module object produced by this load, or undefined.
-
- -

A LoadRequest object is an ordinary Object, inheriting from Object.prototype with own data properties - whose values corresponding certain fields of a corresonding Load Record. A LoadRequest object is created when the value - of those fields need to be passed to an ECMAScript function. Every LoadRequest object has name, and - metadata properties corresponding to the [[Name]] and [[Metadata]] fields of a Load Record. A LoadRequest - object may also have address and source properties corresponding to the [[Address]] and - [[Source]] fields of a Load record.

-
- -
-

15.2.3.2.1 CreateLoad(name) Abstract Operation

- -

The abstract operation CreateLoad creates and returns a new Load Record. The argument name is either - undefined, indicating an anonymous module, or a normalized module name.

- -

The following steps are taken:

- -
    -
  1. Let load be a new Load Record.
    2. -
  2. Set load.[[Status]] to "loading".
    3. -
  3. Set load.[[Name]] to name.
    4. -
  4. Set load.[[LinkSets]] to a new empty List.
    5. -
  5. Set load.[[Metadata]] to metadata ObjectCreate(%ObjectPrototype%).
    6. -
  6. Set all other fields of load to undefined.
    7. -
  7. Return load.
    8. -
-
- -
-

15.2.3.2.2 CreateLoadRequestObject(name, metadata, address, source) Abstract - Operation

- -

The abstract operation CreateLoadRequestObject performed with arguments name, metadata, and - optional arguments address and source returns a new LoadRequest Object. It performs the following - steps:

- -
    -
  1. Let obj be ObjectCreate(%ObjectPrototype%, ()).
    2. -
  2. Assert: The following operations will never result in abrupt - completions.
    3. -
  3. Perform CreateDataProperty (obj, "name", - name).
    4. -
  4. Perform CreateDataProperty (obj, "metadata", - metadata).
    5. -
  5. If address was passed, then perform CreateDataProperty (obj, - "address", address).
    6. -
  6. If source was passed, then perform CreateDataProperty (obj, - "source", source).
    7. -
  7. Return obj.
    8. -
-
-
-
- -
-
-

15.2.4 Runtime Semantics: Module Loading

-
- -
-

15.2.4.1 - LoadModule(loader, name, options) Abstract Operation

- -

The following steps are taken:

- -
    -
  1. Assert: loader is a Loader record.
    2. -
  2. Let name be ToString(name).
    3. -
  3. ReturnIfAbrupt(name).
    4. -
  4. Let address be GetOption(options, "address").
    5. -
  5. ReturnIfAbrupt(address).
    6. -
  6. If address is undefined, let step be "locate".
    7. -
  7. Else, let step be "fetch".
    8. -
  8. Let metadata be ObjectCreate(%ObjectPrototype%).
    9. -
  9. Return PromiseOfStartLoadPartwayThrough( step, - loader, name, metadata, source, address).
    10. -
-
- -
-
-

15.2.4.2 - RequestLoad(loader, request, refererName, refererAddress) Abstract Operation

- -

The RequestLoad abstract operation normalizes the given module name, request, and returns a Promise object - that resolves to the value of a Load object for the given module.

- -

The loader argument is a Loader record.

- -

request is the (non-normalized) name of the module to be imported, as it appears in the import-declaration - or as the argument to loader.load() or loader.import().

- -

refererName and refererAddress provide information about the context of the - import() call or import-declaration. This information is passed to all the loader hooks.

- -

If the requested module is already in the loader's module registry, RequestLoad returns a Promise object - for a Load with the [[Status]] field set to "linked". If the requested module is loading or loaded but not - yet linked, RequestLoad returns a Promise object for an existing Load object from loader.[[Loads]]. - Otherwise, RequestLoad starts loading the module and returns a Promise object for a new Load Record.

- -

The following steps are taken:

- -
    -
  1. Let F be a new anonymous function as defined by CallNormalize.
    2. -
  2. Set F’s [[Loader]] internal slot to - loader.
    3. -
  3. Set F’s [[Request]] internal slot to - request.
    4. -
  4. Set F’s [[RefererName]] internal slot - to refererName.
    5. -
  5. Set F’s [[RefererAddress]] internal - slot to refererAddress.
    6. -
  6. Let p be PromiseNew(F).
    7. -
  7. Let G be a new built-in function as defined by GetOrCreateLoad.
    8. -
  8. Set G’s [[Loader]] internal slot to - loader.
    9. -
  9. Return PromiseThen(p, G).
    10. -
-
- -
-

15.2.4.2.1 CallNormalize(resolve, reject) Functions

- -

A CallNormalize function is an anonymous built-in function that calls a loader's normalize hook.

- -

Each CallNormalize function has internal slots [[Loader]], [[Request]], [[RefererName]], and [[RefererAddress]].

- -

When a CallNormalize function F is called with arguments resolve and reject, the - following steps are taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let request be F’s [[Request]] internal slot.
    3. -
  3. Let refererName be the value of F’s [[RefererName]] internal slot.
    4. -
  4. Let refererAddress be the value of F’s [[RefererAddress]] internal slot.
    5. -
  5. Let loaderObj be loader.[[LoaderObj]].
    6. -
  6. Let normalizeHook be Get(loaderObj, "normalize").
    7. -
  7. Let name be the result of calling the [[Call]] internal method of normalizeHook passing - loaderObj and (request, refererName, refererAddress) as arguments.
    8. -
  8. ReturnIfAbrupt(name).
    9. -
  9. Return the result of calling the [[Call]] internal method of resolve passing undefined and - (name) as arguments.
    10. -
-
- -
-

15.2.4.2.2 GetOrCreateLoad(name) Functions

- -

A GetOrCreateLoad function is an anonymous function that gets or creates a Load Record for a given module - name.

- -

Each GetOrCreateLoad function has a [[Loader]] internal - slot.

- -

When a GetOrCreateLoad function F is called with argument name, the following steps are - taken:

- -
    -
  1. Let loader be F’s [[Loader]] internal slot.
    2. -
  2. Let name be ToString(name).
    3. -
  3. ReturnIfAbrupt(name).
    4. -
  4. Let modules be the value of loaderRecord.[[Modules]],
    5. -
  5. Repeat for each Record {[[key]], [[value]]} p that is an element of loader.[[Modules], do -
      -
    1. If SameValue(p.[[key]], name) is true, then -
        -
      1. Let existingModule be the [[value]] field of that Record.
        2. -
      2. Let load be CreateLoad(name).
        3. -
      3. Set load.[[Status]] to "linked".
        4. -
      4. Set load.[[Module]] to existingModule.
        5. -
      5. Return load.
        6. -
      -
      2. -
    -
    6. -
  6. Repeat for each Record load that is an element of loader.[[Loads]], do -
      -
    1. If SameValue(load.[[Name]], name) is true, then -
        -
      1. Assert: load.status is either "loading" or - "loaded".
        2. -
      2. Return load.
        3. -
      -
      2. -
    -
    7. -
  7. Let load be CreateLoad(name).
    8. -
  8. Append load to the end of the List - loader.[[Loads]].
    9. -
  9. Call ProceedToLocate(loader, load).
    10. -
  10. Return load.
    11. -
-
-
- -
-
-

15.2.4.3 ProceedToLocate(loader, load, p) Abstract Operation

- -

The ProceedToLocate abstract operation continues the asynchronous loading process at the locate - hook.

- -

ProceedToLocate performs the following steps:

- -
    -
  1. Let p be PromiseOf(undefined).
    2. -
  2. Let F be a new built-in function object as defined in CallLocate.
    3. -
  3. Set F’s [[Loader]] internal slot to - loader.
    4. -
  4. Set F’s [[Load]] internal slot to - load.
    5. -
  5. Let p be PromiseThen(p, F).
    6. -
  6. Return ProceedToFetch(loader, load, p).
    7. -
-
- -
-

15.2.4.3.1 CallLocate Functions

- -

A CallLocate function is an anonymous built-in function that calls the locate loader hook. Each - CallLocate function has [[Loader]] and [[Load]] internal slots.

- -

When a CallLocate function F is called, the following steps are taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let load be the value of F’s [[Load]] internal slot.
    3. -
  3. Let loaderObj be loader.[[LoaderObj]].
    4. -
  4. Let hook be Get(loaderObj, "locate").
    5. -
  5. ReturnIfAbrupt(hook).
    6. -
  6. If IsCallable(hook) is false, throw a TypeError exception.
    7. -
  7. Let obj be CreateLoadRequestObject(load.[[Name]], - load.[[Metadata]]).
    8. -
  8. Return the result of calling the [[Call]] internal method of hook with loader and (obj) as - arguments.
    9. -
-
-
- -
-
-

15.2.4.4 ProceedToFetch(loader, load, p) Abstract Operation

- -

The ProceedToFetch abstract operation continues the asynchronous loading process at the fetch hook by - performing the following steps:

- -
    -
  1. Let F be a new built-in function object as defined in CallFetch.
    2. -
  2. Set F’s [[Loader]] internal slot to - loader.
    3. -
  3. Set F’s [[Load]] internal slot to - load.
    4. -
  4. Set F’s [[AddressPromise]] internal - slot to p.
    5. -
  5. Let p be PromiseThen(p, F).
    6. -
  6. Return ProceedToTranslate(loader, load, p).
    7. -
-
- -
-

15.2.4.4.1 CallFetch(address) Functions

- -

A CallFetch function is an anonymous built-in function that calls the fetch loader hook. Each CallFetch - function has [[Loader]] and [[Load]] internal slots.

- -

When a CallFetch function F is called with argument address, the following steps are taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let load be the value of F’s [[Load]] internal slot.
    3. -
  3. If load.[[LinkSets]] is an empty List, return - undefined.
    4. -
  4. Set load.[[Address]] to address.
    5. -
  5. Let loaderObj be loader.[[LoaderObj]].
    6. -
  6. Let hook be Get(loaderObj, "fetch").
    7. -
  7. ReturnIfAbrupt(hook).
    8. -
  8. If IsCallable(hook) is false, throw a TypeError exception.
    9. -
  9. Let obj be CreateLoadRequestObject(load.[[Name]], - load.[[Metadata]], address).
    10. -
  10. Return the result of calling the [[Call]] internal method of hook with loader and (obj) as - arguments.
    11. -
-
-
- -
-
-

15.2.4.5 ProceedToTranslate(loader, load, p) Abstract Operation

- -

The ProceedToTranslate abstract operation continues the asynchronous loading process at the translate - hook hook by performing performs the following steps:

- -
    -
  1. Let F be a new function object as defined in CallTranslate.
    2. -
  2. Set F’s [[Loader]] internal slot to - loader.
    3. -
  3. Set F’s [[Load]] internal slot to - load.
    4. -
  4. Let p be PromiseThen(p, F).
    5. -
  5. Let F be a new function object as defined in CallInstantiate.
    6. -
  6. Set F’s [[Loader]] internal slot to - loader.
    7. -
  7. Set F’s [[Load]] to internal slot - load.
    8. -
  8. Let p be PromiseThen(p, F).
    9. -
  9. Let F be a new function object as defined in InstantiateSucceeded.
    10. -
  10. Set F’s [[Loader]] to internal slot - loader.
    11. -
  11. Set F’s [[Load]] to internal slot - load.
    12. -
  12. Let p be PromiseThen(p, F).
    13. -
  13. Let F be a new function object as defined in LoadFailed.
    14. -
  14. Set F’s [[Load]] internal slot to - load.
    15. -
  15. Return PromiseCatch(p, F).
    16. -
-
- -
-

15.2.4.5.1 CallTranslate Functions

- -

A CallTranslate function is an anonymous built-in function that calls the translate loader hook. Each - CallTranslate function has [[Loader]] and [[Load]] internal slots.

- -

When a CallTranslate function F is called with argument source, the following steps are - taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let load be the value of F’s [[Load]] internal slot.
    3. -
  3. If load.[[LinkSets]] is an empty List, return - undefined.
    4. -
  4. Let hook be Get(loader, "translate").
    5. -
  5. ReturnIfAbrupt(hook).
    6. -
  6. If IsCallable(hook) is false, throw a TypeError exception.
    7. -
  7. Let obj be CreateLoadRequestObject(load.[[Name, - load.[[Metadata]], ", load.[[Address]], source).
    8. -
  8. Return the result of calling the [[Call]] internal method of hook with loader and (obj) as - arguments.
    9. -
-
- -
-

15.2.4.5.2 CallInstantiate Functions

- -

A CallInstantiate function is an anonymous built-in function that calls the instantiate - loader hook. Each CallInstantiate function has [[Loader]] and [[Load]] internal slots.

- -

When a CallInstantiate function F is called with argument source, the following steps are - taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let load be the value of F’s [[Load]] internal slot.
    3. -
  3. If load.[[LinkSets]] is an empty List, return - undefined.
    4. -
  4. Set load.[[Source]] to source.
    5. -
  5. Let loaderObj be loader.[[LoaderObj]].
    6. -
  6. Let hook be Get(loaderObj, "instantiate").
    7. -
  7. ReturnIfAbrupt(hook).
    8. -
  8. If IsCallable(hook) is false, throw a TypeError exception.
    9. -
  9. Let obj be CreateLoadRequestObject(load.[[Name]], - load.[[Metadata]], load.[[Address]], source).
    10. -
  10. Return the result of calling the [[Call]] internal method of hook with loader and (obj) as - arguments.
    11. -
-
- -
-

15.2.4.5.3 InstantiateSucceeded(instantiateResult) Functions

- -

An InstantiateSucceeded function is an anonymous function that handles the result of the instantiate - hook.

- -

Each InstantiateSucceeded function has [[Loader]] and [[Load]] internal slots.

- -

When an InstantiateSucceeded function F is called with argument instantiateResult, the - following steps are taken:

- -
    -
  1. Let loader be the value of F’s [[Loader]] internal slot.
    2. -
  2. Let load be the value of F’s [[Load]] internal slot.
    3. -
  3. If load.[[LinkSets]] is an empty List, return - undefined.
    4. -
  4. If instantiateResult is undefined, then -
      -
    1. Let body be the result of parsing load.[[Source]], interpreted as UTF-16 encoded Unicode text as - described in 10.1.1, using Module as the goal - symbol. Throw a SyntaxError exception if the parse fails or if any static semantics errors are - detected.
      2. -
    2. Set load.[[Body]] to body.
      3. -
    3. Set load.[[Kind]] to declarative.
      4. -
    4. Let depsList be the ModuleRequests of body.
      5. -
    -
    5. -
  5. Else if Type(instantiateResult) is Object, then -
      -
    1. Let deps be Get(instantiateResult, "deps").
      2. -
    2. ReturnIfAbrupt(deps).
      3. -
    3. If deps is undefined, then let depsList be a new empty List.
      4. -
    4. Else, -
        -
      1. Let depsList be IterableToArray(deps).
        2. -
      2. ReturnIfAbrupt(depsList).
        3. -
      -
      5. -
    5. Let execute be Get(instantiateResult, "execute").
      6. -
    6. ReturnIfAbrupt(execute).
      7. -
    7. Set load.[[Execute]] to execute.
      8. -
    8. Set load.[[Kind]] to dynamic.
      9. -
    -
    6. -
  6. Else, -
      -
    1. Throw a TypeError exception.
      2. -
    -
    7. -
  7. Return ProcessLoadDependencies(load, loader, - depsList).
    8. -
-
- -
-

15.2.4.5.4 LoadFailed Functions

- -

A LoadFailed function is an anonymous function that marks a Load Record as having failed. All LinkSets that depend on - the Load also fail.

- -

Each LoadFailed function has a [[Load]] internal - slot.

- -

When a LoadFailed function F is called with argument exc, the following steps are taken:

- -
    -
  1. Let load be the value of F’s [[Load]] internal slot.
    2. -
  2. Assert: load.[[Status]] is "loading".
    3. -
  3. Set load.[[Status]] to `"failed".
    4. -
  4. Set load.[[Exception]] to exc.
    5. -
  5. Let linkSets be a copy of the List - load.[[LinkSets]].
    6. -
  6. For each linkSet in linkSets, in the order in which the LinkSet - Records were created, -
      -
    1. Call LinkSetFailed(linkSet, exc).
      2. -
    -
    7. -
  7. Assert: load.[[LinkSets]] is empty.
    8. -
-
-
- -
-
-

15.2.4.6 ProcessLoadDependencies(load, loader, depsList) Abstract - Operation

- -

The ProcessLoadDependencies abstract operation is called after one module has nearly finished loading. It starts new - loads as needed to load the module's dependencies.

- -

ProcessLoadDependencies also arranges for LoadSucceeded to be called.

- -

The following steps are taken:

- -
    -
  1. Let refererName be load.[[Name]].
    2. -
  2. Set load.[[Dependencies]] to a new empty List.
    3. -
  3. Let loadPromises be a new empty List.
    4. -
  4. For each request in depsList, do -
      -
    1. Let p be RequestLoad(loader, request, refererName, - load.[[Address]]).
      2. -
    2. Let F be a new built-in function as defined by AddDependencyLoad.
      3. -
    3. Set the [[Load]] internal slot of F to - load.
      4. -
    4. Set the [[Request]] internal slot of F to - request.
      5. -
    5. Let p be PromiseThen(p, F).
      6. -
    6. Append p as the last element of loadPromises.
      7. -
    -
    5. -
  5. Let p be PromiseAll(loadPromises).
    6. -
  6. Let F be a new built-in function as defined by LoadSucceeded.
    7. -
  7. Set the [[Load]] internal slot of F to - load.
    8. -
  8. Return PromiseThen(p, F).
    9. -
-
- -
-

15.2.4.6.1 AddDependencyLoad(depLoad) Functions

- -

An AddDependencyLoad function is an anonymous function that adds a Load Record for a dependency to any LinkSets - associated with the parent Load.

- -

Each AddDependencyLoad function has [[ParentLoad]] and [[Request]] internal slots.

- -

When an AddDependencyLoad function F is called with argument depLoad, the following steps are - taken:

- -
    -
  1. Let parentLoad be the value of F’s [[ParentLoad]] internal slot.
    2. -
  2. Let request be the value of F’s [[Request]] internal slot.
    3. -
  3. Assert: There is no Record in the List parentLoad.[[Dependencies]] whose [[key]] field is - equal to request.
    4. -
  4. Append the Record {[[key]]: request, [[value]]: depLoad.[[Name]]} to the end of the List parentLoad.[[Dependencies]].
    5. -
  5. If depLoad.[[Status]] is not "linked", then -
      -
    1. Let linkSets be a copy of the List - parentLoad.[[LinkSets]].
      2. -
    2. For each linkSet in linkSets, do -
        -
      1. Call AddLoadToLinkSet(linkSet, depLoad).
        2. -
      -
      3. -
    -
    6. -
-
- -
-

15.2.4.6.2 LoadSucceeded Functions

- -

A LoadSucceeded function is an anonymous function that transitions a Load Record from "loading" to - "loaded" and notifies all associated LinkSet Records of the change. This - function concludes the loader pipeline. It is called after all a newly loaded module's dependencies are successfully - processed.

- -

Each LoadSucceeded function has a [[Load]] internal - slot.

- -

When a LoadSucceeded function F is called, the following steps are taken:

- -
    -
  1. Let load be the value of F’s [[Load]] internal slot.
    2. -
  2. Assert: load.[[Status]] is "loading".
    3. -
  3. Set load.[[Status]] to "loaded".
    4. -
  4. Let linkSets be a copy of load.[[LinkSets]].
    5. -
  5. For each linkSet in linkSets in List order, do -
      -
    1. Call UpdateLinkSetOnLoad(linkSet, load).
      2. -
    -
    6. -
-
-
- -
-
-

15.2.4.7 PromiseOfStartLoadPartwayThrough (step, loader, name, metadata, - source, address)

-
    -
  1. Let F be a new anonymous function object as defined in AsyncStartLoadPartwayThrough.
    2. -
  2. Let state be the Record { [[Step]]: "translate", [[Loader]]: loader, [[ModuleName]]: - name, [[ModuleMetadata]]: metadata, [[ModuleSource]]: source, [[ModuleAddress]]: - address}.
    3. -
  3. Set F’s [[StepState]] internal slot to - state.
    4. -
  4. Return PromiseNew(F).
    5. -
-
- -
-

15.2.4.7.1 AsyncStartLoadPartwayThrough Functions

- -

An AsyncStartLoadPartwayThrough function is an anonymous function that is used as a Promise executor. When called it - creates a new Load Record and populates it with some information provided by the caller, so that loading can proceed - from either the locate hook, the fetch hook, or the translate hook. This - functionality is used to implement builtin methods like Reflect.Loader.prototype.load, which permits the user to specify - both the normalized module name and the address.

- -

Each AsyncStartLoadPartwayThrough function has internal slots [[StepState]].

- -

When an AsyncStartLoadPartwayThrough function F is called with arguments resolve and - reject, the following steps are taken:

- -
    -
  1. Let state be the value of F’s [[StepState]] internal slot.
    2. -
  2. Let loader be state.[[Loader]].
    3. -
  3. Let name be state.[[ModuleName]].
    4. -
  4. Let step be state.[[Step]].
    5. -
  5. Repeat for each Record {[[key]], [[value]]} p that is an element of loader.[[Modules], do -
      -
    1. If SameValue(p.[[key]], name) is true, then throw a - TypeError exception.
      2. -
    -
    6. -
  6. Repeat for element of load or loader.[[Modules], do -
      -
    1. If SameValue(loads.[[Name]], name) is true, then throw a - TypeError exception.
      2. -
    -
    7. -
  7. Let load be CreateLoad(name).
    8. -
  8. Set load.[[Metadata]] to state.[[ModuleMetadata]].
    9. -
  9. Let linkSet be CreateLinkSet(loader, load).
    10. -
  10. Append load to the end of loader.[[Loads]].
    11. -
  11. Call the [[Call]] internal method of resolve with arguments undefined and - (linkSet.[[Done]]).
    12. -
  12. If step is "locate", -
      -
    1. Call ProceedToLocate(loader, load).
      2. -
    -
    13. -
  13. Else if step is "fetch", -
      -
    1. Let addressPromise be PromiseOf(state.[[ModuleAddress]]).
      2. -
    2. Call ProceedToFetch(loader, load, addressPromise).
      3. -
    -
    14. -
  14. Else, -
      -
    1. Assert: step is "translate".
      2. -
    2. Set load.[[Address]] to state.[[ModuleAddress]].
      3. -
    3. Let sourcePromise be PromiseOf(state.[[ModuleSource]]).
      4. -
    4. Call ProceedToTranslate(loader, load, - sourcePromise).
      5. -
    -
    15. -
-
-
-
- -
-
-

15.2.5 Runtime Semantics: Module Linking

-
- -
-
-

15.2.5.1 ModuleLinkage Record

- -

A ModuleLinkage Record contains the state needed to link a specific module.

- -

Each LinkSet Record has the fields defined in Table 36.

- -
-
Table 36 — ModuleLinkage Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValue TypeMeaning
[[Body]]a parse resultThe parse of a Module production
[[BoundNames]]
[[KnownExportEntries]]
[[KnownExportEntries]]
[[ExportDefinitions]]
[[Exports]]
[[Dependenies]]
[[UnlinkedDependencies]]
[[ImportedEntries]]
[[ImportedDefinitions]]
[[LinkErrors]]
[[Environment]]
-
-
- -
-

15.2.5.1.1 CreateModuleLinkageRecord (loader, body) Abstract Operation

- -

The abstract operation CreateModuleLinkageRecord with arguments loader and body performs the - following steps:

- -
    -
  1. Assert: body is a Modulebody parse.
    2. -
  2. Let M be a new object with [[Prototype]] null.
    3. -
  3. Set M.[[Body]] to body.
    4. -
  4. Set M.[[BoundNames]] to DeclaredNames of body.
    5. -
  5. Set M.[[KnownExportEntries]] to KnownExportEntries of body.
    6. -
  6. Set M.[[UnknownExportEntries]] to UnknownExportEntries of body.
    7. -
  7. Set M.[[ExportDefinitions]] to undefined.
    8. -
  8. Set M.[[Exports]] to undefined.
    9. -
  9. Set M.[[Dependencies]] to undefined.
    10. -
  10. Set M.[[UnlinkedDependencies]] to undefined.
    11. -
  11. Set M.[[ImportEntries]] to ImportEntries of body.
    12. -
  12. Set M.[[ImportDefinitions]] to undefined.
    13. -
  13. Set M.[[LinkErrors]] to a new empty List.
    14. -
  14. Let realm be loader.[[Realm]].
    15. -
  15. Let globalEnv be realm.[[globalEnv]].
    16. -
  16. Let env be NewModuleEnvironment(globalEnv).
    17. -
  17. Set M.[[Environment]] to env.
    18. -
  18. Return M.
    19. -
-
- -
-

15.2.5.1.2 LookupExport ( M, exportName )

- -

The abstract operation LookupExport with arguments M and exportName performs the following:

- -
    -
  1. If M.[[Exports]] does not contain a record export such that export.[[ExportName]] is equal to - exportName, then return undefined.
    2. -
  2. Let export be the record in M.[[Exports]] such that export.[[ExportName]] is equal to - exportName.
    3. -
  3. Return export.[[Binding]].
    4. -
-
- -
-

15.2.5.1.3 LookupModuleDependency ( M, requestName )

- -

The abstract operation LookupModuleDependency with arguments M and requestName performs the - following steps:

- -
    -
  1. Assert: M is a ModuleLinkage - Record.
    2. -
  2. If requestName is null then return M.
    3. -
  3. Let pair be the record in M.[[Dependencies]] such that pair.[[Key]] is equal to - requestName.
    4. -
  4. Return pair.[[Module]].
    5. -
-
-
- -
-
-

15.2.5.2 LinkSet Records

- -

A LinkSet Record represents a call to loader.define(), .load(), .module(), or - .import().

- -

Each LinkSet Record has the fields defined in Table 37.

- -
-
Table 37 — LinkSet Record Fields
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Field NameValue TypeMeaning
[[Loader]]Loader RecordThe Loader record that created this LinkSet.
[[Loads]]List of Load RecordA List of the Load Records that must finish loading before the modules can be linked and evaluated.
[[Done]]Promise ObjectThe Promise that becomes fulfilled when all dependencies are loaded and linked together.
[[Resolve]]Function ObjectFunction used to resolve [[Done]].
[[Reject]]Function ObjectFunction used to reject [[Done]].
-
-
- -
-

15.2.5.2.1 CreateLinkSet(loader, startingLoad) Abstract Operation

- -

The CreateLinkSet abstract operation creates a new LinkSet record by performing the following steps:

- -
    -
  1. Assert: loader is a Loader Record.
    2. -
  2. If loader does not have all of the internal properties of a Loader Instance, throw a TypeError - exception.
    3. -
  3. Let promiseCapability be PromiseBuiltinCapability().
    4. -
  4. ReturnIfAbrupt(promiseCapability).
    5. -
  5. Let linkSet be LinkSet {[[Loader]]: loader, [[Loads]]: ( ), [[Done]]: - promiseCapability.[[Promise]], [[Resolve]]: promiseCapability.[[Resolve]], [[Reject]]: - promiseCapability.[[Reject]] }.
    6. -
  6. Perform AddLoadToLinkSet(linkSet, startingLoad).
    7. -
  7. Return linkSet.
    8. -
-
- -
-

15.2.5.2.2 AddLoadToLinkSet(linkSet, load) Abstract Operation

- -

The AddLoadToLinkSet abstract operation associates a LinkSet Record with a Load Record and each of its currently - known dependencies, indicating that the LinkSet cannot be linked until those Loads have finished successfully.

- -

The following steps are taken:

- -
    -
  1. Assert: load.[[Status]] is either "loading" or - "loaded".
    2. -
  2. Let loader be linkSet.[[Loader]].
    3. -
  3. If load is not already an element of the List - linkSet.[[Loads]], -
      -
    1. Append load to the end of the List - linkSet.[[Loads]].
      2. -
    2. Append linkSet to the end of the List - load.[[LinkSets]].
      3. -
    3. If load.[[Status]] is "loaded", then -
        -
      1. Repeat for each r that is a Record {[[Name]], [[NormalizedName]]} in load.[[Dependencies]], -
          -
        1. If there is no element of loader.[[Modules]] whose [[key]] field is equal to name, -
            -
          1. If there is an element of loader.[[Loads]] whose [[Name]] field is equal to name, -
              -
            1. Let depLoad be that Load Record.
              2. -
            2. Perform AddLoadToLinkSet(linkSet, depLoad).
              3. -
            -
            2. -
          -
          2. -
        -
        2. -
      -
      4. -
    -
    4. -
-
- -
-

15.2.5.2.3 UpdateLinkSetOnLoad(linkSet, load) Abstract Operation

- -

The UpdateLinkSetOnLoad abstract operation is called immediately after a Load successfully finishes, after starting - Loads for any dependencies that were not already loading, loaded, or in the module registry.

- -

This operation determines whether linkSet is ready to link, and if so, calls Link.

- -

The following steps are taken:

- -
    -
  1. Assert: load is an element of linkSet.[[Loads]].
    2. -
  2. Assert: load.[[Status]] is either "loaded" or - "linked".
    3. -
  3. Repeat for each element in linkSet.[[Loads]], -
      -
    1. If element.[[Status]] is "loading", then return.
      2. -
    -
    4. -
  4. Assert: All Loads in linkSet.[[Loads]] have finished loading.
    5. -
  5. Let startingLoad be the first element of the List - linkSet.[[Loads]].
    6. -
  6. Let status be Link(linkSet.[[Loads]], linkSet.[[Loader]]).
    7. -
  7. If status is an abrupt completion, then -
      -
    1. Return LinkSetFailed(linkSet, status.[[value]]).
      2. -
    -
    8. -
  8. Assert: linkSet.[[Loads]] is an empty List.
    9. -
  9. Call the [[Call]] internal method of linkSet.[[Resolve]] passing undefined and (startingLoad) - as arguments.
    10. -
  10. Assert: The call performed by step 9 completed normally.
    11. -
-
- -
-

15.2.5.2.4 LinkSetFailed(linkSet, exc) Abstract Operation

- -

The LinkSetFailed abstract operation is called when a LinkSet fails. It detaches the given LinkSet Record from all - Load Records and rejects the linkSet.[[Done]] Promise.

- -

The following steps are taken:

- -
    -
  1. Let loader be linkSet.[[Loader]].
    2. -
  2. Let loads be a copy of the List - linkSet.[[Loads]].
    3. -
  3. For each load in loads, -
      -
    1. Assert: linkSet is an element of the List load.[[LinkSets]].
      2. -
    2. Remove linkSet from the List - load.[[LinkSets]].
      3. -
    3. If load.[[LinkSets]] is empty and load is an element of loader.[[Loads]], then -
        -
      1. Remove load from the List - loader.[[Loads]].
        2. -
      -
      4. -
    -
    4. -
  4. Return the result of calling [[Call]] internal method of linkSet.[[Reject]] passing undefined and - (exc) as arguments.
    5. -
  5. Assert: The call performed by step 4 completed normally.
    6. -
-
- -
-

15.2.5.2.5 FinishLoad(loader, load) Abstract Operation

- -

The FinishLoad Abstract Operation removes a completed Load Record from all LinkSets and commits the newly loaded - Module to the registry. It performs the following steps:

- -
    -
  1. Let name be load.[[Name]].
    2. -
  2. If name is not undefined, then -
      -
    1. Assert: There is no Record {[[key]], [[value]]} p that is an - element of loader.[[Modules]], such that SameValue(p.[[key]], - load.[[Name]]) is true.
      2. -
    2. Append the Record {[[key]]: load.[[Name]], [[value]]: load.[[Module]]} as the last element of - loader.[[Modules]].
      3. -
    -
    3. -
  3. If load is an element of the List - loader.[[Loads]], then -
      -
    1. Remove load from the List - loader.[[Loads]].
      2. -
    -
    4. -
  4. For each linkSet in load.[[LinkSets]], -
      -
    1. Remove load from linkSet.[[Loads]].
      2. -
    -
    5. -
  5. Remove all elements from the List - load.[[LinkSets]].
    6. -
-
-
- -
-
-

15.2.5.3 Module Linking Groups

- -

A load record load1 has a linkage - dependency on a load record load2 if load2 is contained in load1.[[UnlinkedDependencies]] or there exists a load record load in load1.[[UnlinkedDependencies]] such that load - has a linkage dependency on load2.

- -

The linkage graph of a List, list, of load records is the set of load records load such - that some load record in list has a linkage dependency on load.

- -

A dependency chain from load1 to - load2 is a List of load records demonstrating the transitive linkage dependency - from load1 to load2.

- -

A dependency cycle is a dependency chain whose first and last elements’ [[Name]] fields have the - same value.

- -

A dependency chain is cyclic if it contains a subsequence that is a dependency cycle. A dependency - chain is acyclic if it is not cyclic.

- -

A dependency chain is mixed if there are two elements with distinct values for their [[Kind]] fields. A - dependency group transition of kind kind is a two-element subsequence load1, load2 of a dependency chain such that load1.[[Kind]] is not equal to kind and load2.[[Kind]] is equal to kind.

- -

The dependency group count of a dependency chain with first element load1 is the number of distinct dependency group transitions of kind load1.[[Kind]].

-
- -
-

15.2.5.3.1 LinkageGroups ( start )

- -

The abstract operation LinkageGroups with argument start performs the following steps:

- -
    -
  1. Assert: start is a List of LinkSet - Records.
    2. -
  2. Let G be the linkage graph of start.
    3. -
  3. If there are any mixed dependency cycles in G, throw a new Syntax Error.
    4. -
  4. For each load in G, do -
      -
    1. Let n be the largest dependency group count of all acyclic dependency chains in G starting from - load.
      2. -
    2. Set load.[[GroupIndex]] to n.
      3. -
    -
    5. -
  5. Let declarativeGroupCount be the largest [[GroupIndex]] of any load in G such that - load.[[Kind]] is declarative.
    6. -
  6. Let declarativeGroups be a new List of length - declarativeGroupCount where each element is a new empty List.
    7. -
  7. Let dynamicGroupCount be the largest [[GroupIndex]] of any load in G such that - load.[[Kind]] is dynamic.
    8. -
  8. Let dynamicGroups be a new List of length - dynamicGroupCount where each element is a new empty List.
    9. -
  9. Let visited be a new empty List.
    10. -
  10. For each load in start, do -
      -
    1. Perform BuildLinkageGroups(load, declarativeGroups, - dynamicGroups, and visited).
      2. -
    -
    11. -
  11. If any load in the first element of declarativeGroups has a dependency on a load record of [[Kind]] - dynamic, then -
      -
    1. Let groups be a List constructed by interleaving - the elements of dynamicGroups and declarativeGroups, starting with the former.
      2. -
    -
    12. -
  12. Else, -
      -
    1. let groups be a List constructed by interleaving - the elements of declarativeGroups and dynamicGroups, starting with the former.
      2. -
    -
    13. -
  13. Return groups.
    14. -
-
- -
-

15.2.5.3.2 BuildLinkageGroups ( load, declarativeGroups, dynamicGroups, - visited )

- -

The abstract operation BuildLinkageGroups with arguments load, declarativeGroups, and - dynamicGroups performs the following steps:

- -
    -
  1. If visited contains an element whose [[Name]] is equal to load.[[Name]], then return.
    2. -
  2. Add load to visited.
    3. -
  3. For each dep of load.[[UnlinkedDependencies]], do -
      -
    1. Call the BuildLinkageGroups abstract operation passing dep, declarativeGroups, - dynamicGroups, and visited as arguments.
      2. -
    -
    4. -
  4. Let i be load.[[GroupIndex]].
    5. -
  5. If load.[[Kind]] is declarative let groups be - declarativeGroups; otherwise let groups be dynamicGroups.
    6. -
  6. Let group be the ith element of groups.
    7. -
  7. Add load to group.
    8. -
-
-
- - - -
-
-

15.2.5.5 LinkDeclarativeModules ( loads, loader )

- -

The abstract operation LinkDeclarativeModules with arguments loads and loader performs the - following steps:

- -
    -
  1. Let unlinked be a new empty List.
    2. -
  2. For each load in loads, do -
      -
    1. If load.[[Status]] is not linked, then -
        -
      1. Let module be CreateModuleLinkageRecord - (loader, load.[[Body]]).
        2. -
      2. Let pair be the record {[[Module]]: module, [[Load]]: load}.
        3. -
      3. Add pair to unlinked.
        4. -
      -
      2. -
    -
    3. -
  3. For each pair in unlinked, do -
      -
    1. Let resolvedDeps be a new empty List.
      2. -
    2. Let unlinkedDeps be a new empty List.
      3. -
    3. For each element dep in pair.[[Load]].[[Dependencies]], do -
        -
      1. Let requestName be dep.[[Key]].
        2. -
      2. Let normalizedName be dep.[[Value]].
        3. -
      3. If loads contains a record load such that SameValue(load.[[Name]], normalizedName) is true, then -
          -
        1. If load.[[Status]] is linked, then -
            -
          1. Let resolvedDep be the record {[[Key]]: requestName, [[Value]]: - load.[[Module]]}.
            2. -
          2. Add resolvedDep to resolvedDeps.
            3. -
          -
          2. -
        2. Else, -
            -
          1. Let otherPair be the record in unlinked such that SameValue(otherPair.[[Load]].[[Name]], normalizedName) is - true.
            2. -
          2. Add the record {[[Key]]: requestName, [[Value]]: otherPair.[[Module]]} to - resolvedDeps.
            3. -
          3. Add otherPair.[[Load]] to unlinkedDeps.
            4. -
          -
          3. -
        -
        4. -
      4. Else, -
          -
        1. Let module be LoaderRegistryLookup(loader, normalizedName).
          2. -
        2. If module is null then -
            -
          1. Let error be a new ReferenceError exception.
            2. -
          2. Add error to pair.[[Module]].[[LinkErrors]].
            3. -
          -
          3. -
        3. Else, add the record {[[Key]]: requestName, [[Value]]: module} to - resolvedDeps.
          4. -
        -
        5. -
      -
      4. -
    4. Set pair.[[Module]].[[Dependencies]] to resolvedDeps.
      5. -
    5. Set pair.[[Module]].[[UnlinkedDependencies]] to unlinkedDeps.
      6. -
    -
    4. -
  4. For each pair in unlinked, do -
      -
    1. Perform ResolveExportEntries(pair.[[Module]], ( ) ).
      2. -
    2. Perform ResolveExports(pair.[[Module]]).
      3. -
    -
    5. -
  5. For each pair in unlinked, do -
      -
    1. Perform ResolveImportEntries(pair.[[Module]]).
      2. -
    2. Perform LinkImports(pair.[[Module]]).
      3. -
    -
    6. -
  6. If there exists a pair in unlinked such that pair.[[Module]].[[LinkErrors]] is not empty, - choose one of the link errors and throw it.
    7. -
  7. For each pair in unlinked, do -
      -
    1. Set pair.[[Load]].[[Module]] to pair.[[Module]].
      2. -
    2. Set pair.[[Load]].[[Status]] to linked.
      3. -
    3. Let r beFinishLoad(loader, pair.[[Load]]).
      4. -
    4. ReturnIfAbrupt(r).
      5. -
    -
    8. -
-
- -
-

15.2.5.5.1 LinkImports ( M )

- -

The abstract operation LinkImports with argument M performs the following steps:

- -
    -
  1. Let envRec be M.[[Environment]].
    2. -
  2. Let defs be M.[[ImportDefinitions]].
    3. -
  3. For each def in defs, do -
      -
    1. If def.[[ImportName]] is module, then the following steps are taken: -
        -
      1. Call the CreateImmutableBinding concrete method of envRec passing def.[[LocalName]] as the - argument.
        2. -
      2. Call the InitializeImmutableBinding concrete method of envRec passing def.[[LocalName]] and - def.[[Module]] as the arguments.
        3. -
      -
      2. -
    2. Otherwise, the following steps are taken: -
        -
      1. Let binding be ResolveExport(def.[[Module]], - def.[[ImportName]], ( )).
        2. -
      2. If binding is undefined, then the following steps are taken: -
          -
        1. Let error be a new Reference Error.
          2. -
        2. Add error to M.[[LinkErrors]].
          3. -
        -
        3. -
      3. Otherwise, call the CreateImportBinding concrete method of envRec passing def.[[LocalName]] - and binding as the arguments.
        4. -
      -
      3. -
    -
    4. -
-
-
- -
-

15.2.5.6 LinkDynamicModules ( loads, loader )

- -

The abstract operation LinkDynamicModules with arguments loads and loader performs the following - steps:

- -
    -
  1. For each load in loads, do -
      -
    1. Let exec be load.[[Execute]].
      2. -
    2. Let module be the result of calling the [[Call]] internal method of exec with undefined as - the this value and with no arguments.
      3. -
    3. ReturnIfAbrupt(module).
      4. -
    4. If module does not have all the internal data properties of a Module Instance Object, then throw a - TypeError exception.
      5. -
    5. Set load.[[Module]] to module.
      6. -
    6. Set load.[[Status]] to linked.
      7. -
    7. Let r be FinishLoad(loader, load).
      8. -
    8. ReturnIfAbrupt(r).
      9. -
    -
    2. -
-
- -
-

15.2.5.7 ResolveExportEntries ( M, visited )

- -

The abstract operation ResolveExportEntries with arguments M and visited performs the following - steps:

- -
    -
  1. If M.[[ExportDefinitions]] is not undefined, then return M.[[ExportDefinitions]].
    2. -
  2. Let defs be a new empty List.
    3. -
  3. Let boundNames be M.[[BoundNames]].
    4. -
  4. For each entry in M.[[KnownExportEntries]], do -
      -
    1. Let modReq be entry.[[ModuleRequest]].
      2. -
    2. Let otherMod be LookupModuleDependency(M, - modReq).
      3. -
    3. If entry.[[Module]] is null and entry.[[LocalName]] is not null and - boundNames does not contain entry.[[LocalName]], then the following steps are taken: -
        -
      1. Let error be a new Reference Error.
        2. -
      2. Add error to M.[[LinkErrors]].
        3. -
      -
      4. -
    4. Add the record {[[Module]]: otherMod, [[ImportName]]: entry.[[ImportName]], [[LocalName]]: - entry.[[LocalName]], [[ExportName]]: entry.[[ExportName]], [[Explicit]]: true} to - defs.
      5. -
    -
    5. -
  5. For each modReq in M.[[UnknownExportEntries]], do -
      -
    1. Let otherMod be LookupModuleDependency( M, - modReq).
      2. -
    2. If otherMod is in visited, then the following steps are taken: -
        -
      1. Let error be a new Syntax Error.
        2. -
      2. Add error to M.[[LinkErrors]].
        3. -
      -
      3. -
    3. Otherwise the following steps are taken: -
        -
      1. Add otherMod to visited.
        2. -
      2. Let otherDefs be ResolveExportEntries(otherMod, visited ).
        3. -
      3. For each def of otherDefs, do -
          -
        1. Add the record {[[Module]]: otherMod, [[ImportName]]: def.[[ExportName]], [[LocalName]]: - null, [[ExportName]]: def.[[ExportName]], [[Explicit]]: false} to defs.
          2. -
        -
        4. -
      -
      4. -
    -
    6. -
  6. Set M.[[ExportDefinitions]] to defs.
    7. -
  7. Return defs.
    8. -
-
- -
-

15.2.5.8 - ResolveExports ( M )

- -

The abstract operation ResolveExports with argument M performs the following steps:

- -
    -
  1. For each def in M.[[ExportDefinitions]], do -
      -
    1. Perform ResolveExport(M, def.[[ExportName]], ( )).
      2. -
    -
    2. -
-
- -
-

15.2.5.9 - ResolveExport ( M, exportName, visited )

- -

The abstract operation ResolveExport with arguments M, exportName, and visited - performs the following steps:

- -
    -
  1. Let exports be M.[[Exports]].
    2. -
  2. If exports has a record export such that export.[[ExportName]] is equal to exportName, - return export.[[Binding]].
    3. -
  3. Let ref be {[[Module]]: M, [[ExportName]]: exportName}.
    4. -
  4. If visited contains a record equal to ref then the following steps are taken: -
      -
    1. Let error be a new Syntax Error.
      2. -
    2. Add error to M.[[LinkErrors]].
      3. -
    3. Return error.
      4. -
    -
    5. -
  5. Let defs be M.[[ExportDefinitions]].
    6. -
  6. Let overlappingDefs be the List of records def - in defs such that def.[[ExportName]] is equal to exportName.
    7. -
  7. If overlappingDefs is empty, then the following steps are taken: -
      -
    1. Let error be a new Reference Error.
      2. -
    2. Add error to M.[[LinkErrors]].
      3. -
    3. Return error.
      4. -
    -
    8. -
  8. If overlappingDefs has more than one record def such that def.[[Explicit]] is true, or - if it has length greater than 1 but contains no records def such that def.[[Explicit]] is true, - then the following steps are taken: -
      -
    1. Let error be a new Syntax Error.
      2. -
    2. Add error to M.[[LinkErrors]].
      3. -
    3. Return error.
      4. -
    -
    9. -
  9. Let def be the unique record in overlappingDefs such that def.[[Explicit]] is true, or - if there is no such record let def be the unique record in overlappingDefs.
    10. -
  10. If def.[[LocalName]] is not null, then the following steps are taken: -
      -
    1. Let binding be the record {[[Module]]: M, [[LocalName]]: def.[[LocalName]]}.
      2. -
    2. Let export be the record {[[ExportName]]: exportName, [[Binding]]: binding}.
      3. -
    3. Add export to exports.
      4. -
    4. Return binding.
      5. -
    -
    11. -
  11. Add ref to visited.
    12. -
  12. Let binding be ResolveExport(def.[[Module]], def.[[ImportName]], visited).
    13. -
  13. Return binding.
    14. -
-
- -
-

15.2.5.10 ResolveImportEntries ( M )

- -

The abstract operation ResolveImportEntries called with argument M performs the following steps:

- -
    -
  1. Let entries be M.[[ImportEntries]].
    2. -
  2. Let defs be a new empty List.
    3. -
  3. For each entry in entries, do -
      -
    1. Let modReq be entry.[[ModuleRequest]].
      2. -
    2. Let otherMod be LookupModuleDependency(M, - modReq).
      3. -
    3. Add the record {[[Module]]: otherMod, [[ImportName]]: entry.[[ImportName]], [[LocalName]]: - entry.[[LocalName]]} to defs.
      4. -
    -
    4. -
  4. Return defs.
    5. -
-
-
- -
-
-

15.2.6 Runtime Semantics: Module Evaluation

- -

Module bodies are evaluated on demand, as late as possible. The loader uses the function EnsureEvaluated, defined below, to run scripts. The loader always calls EnsureEvaluated before returning a Module object to user code.

- -

There is one way a module can be exposed to script before its body has been evaluated. In the case of an import cycle, - whichever module is evaluated first can observe the others before they are evaluated. Simply put, we have to start - somewhere: one of the modules in the cycle must run before the others.

-
- -
-

15.2.6.1 EvaluateLoadedModule(load) Functions

- -

An EvaluateLoadedModule function is an anonymous built-in function that is used by Reflect.Loader.prototype.module and - Reflect.Loader.prototype.import to ensure that a module has been evaluated before it is passed to script code.

- -

Each EvaluateLoadedModule function has a [[Loader]] internal - slot.

- -

When a EvaluateLoadedModule function F is called with argument load, the following steps are - taken:

- -
    -
  1. Let loader be F.[[Loader]].
    2. -
  2. Assert: load.[[Status]] is "linked".
    3. -
  3. Let module be load.[[Module]].
    4. -
  4. Let result be EnsureEvaluated(module, (), loader).
    5. -
  5. ReturnIfAbrupt(result).
    6. -
  6. Return module.
    7. -
-
- -
-

15.2.6.2 - EnsureEvaluated(mod, seen, loader) Abstract Operation

- -

The abstract operation EnsureEvaluated walks the dependency graph of the module mod, evaluating any module - bodies that have not already been evaluated (including, finally, mod itself). Modules are evaluated in - depth-first, left-to-right, post order, stopping at cycles.

- -

mod and its dependencies must already be linked.

- -

The List seen is used to detect cycles. mod - must not already be in the List seen.

- -

On success, mod and all its dependencies, transitively, will have started to evaluate exactly once.

- -

EnsureEvaluated performs the following steps:

- -
    -
  1. If mod.[[Evaluated]] is true, return undefined.
    2. -
  2. Append mod as the last element of seen.
    3. -
  3. TODO: Create the module environment for mod
    4. -
  4. Let deps be mod.[[Dependencies]].
    5. -
  5. For each pair in deps, in List order, -
      -
    1. Let dep be pair.[[value]].
      2. -
    2. If dep is not an element of seen, then -
        -
      1. Call EnsureEvaluated with the arguments dep, seen, and loader.
        2. -
      -
      3. -
    -
    6. -
  6. If mod.[[Evaluated]] is true, return undefined.
    7. -
  7. Set mod.[[Evaluated]] to true.
    8. -
  8. If mod.[[Body]] is undefined, then return undefined.
    9. -
  9. Let status be ModuleDeclarationInstantiation(mod.[[Body]], - mod.[[Environment]]).
    10. -
  10. Let initContext be a new ECMAScript code execution context.
    11. -
  11. Set initContext's Realm to loader.[[Realm]].
    12. -
  12. Set initContext's VariableEnvironment to - mod.[[Environment]].
    13. -
  13. Set initContext's LexicalEnvironment to - mod.[[Environment]].
    14. -
  14. If there is a currently running execution context, suspend it.
    15. -
  15. Push initContext on to the execution context stack; initContext - is now the running execution context.
    16. -
  16. Let r be the result of evaluating mod.[[Body]].
    17. -
  17. Suspend initContext and remove it from the execution context stack.
    18. -
  18. Resume the context, if any, that is now on the top of the execution context - stack as the running execution context.
    19. -
  19. Return r.
    20. -
-
-
-
-
- -
-

16 Error Handling and Language Extensions

- -

An implementation must report most errors at the time the relevant ECMAScript language construct is evaluated. An early - error is an error that can be detected and reported prior to the evaluation of any construct in the Script containing the error. The presense of an early error prevents the evaluation of the construct. An - implementation must report early errors in a Script as part of the ScriptEvaluationTask for that Script. Early errors in a Module are reported at the point when the Module would be evaluated and the Module is never initialized. Early errors in eval code are reported at the time eval is - called and prevent evaluation of the eval code. All errors that are not early errors are runtime errors.

- -

An implementation must report as an early error any occurrence of a condition that is listed in a “Static Semantics: - Early Errors” subclause of this specification.

- -

An implementation shall not treat other kinds of errors as early errors even if the compiler can prove that a construct - cannot execute without error under any circumstances. An implementation may issue an early warning in such a case, but it should - not report the error until the relevant construct is actually executed.

- -

An implementation shall report all errors as specified, except for the following:

- - - -

An implementation may define behaviour other than throwing RangeError for toFixed, - toExponential, and toPrecision when the fractionDigits or precision argument is - outside the specified range.

-
- -
-

17 ECMAScript Standard Built-in Objects

- -

There are certain built-in objects available whenever an ECMAScript Script begins execution. One, the - global object, is part of the lexical environment of the executing program. Others are - accessible as initial properties of the global object or indirectly as properties of accessible built-in objects.

- -

Unless specified otherwise, a built-in object that is callable as a function is a Built-in Function object with the - characteristics described in 9.3. Unless specified otherwise, the [[Extensible]] internal slot of a built-in object initially has the value - true. Every built-in object has a [[Realm]] internal slot - whose value is the code Realm for which the object was initially created.

- -

Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are constructors: they are - functions intended for use with the new operator. For each built-in function, this specification describes the - arguments required by that function and properties of the Function object. For each built-in constructor, this specification - furthermore describes properties of the prototype object of that constructor and properties of specific object instances - returned by a new expression that invokes that constructor.

- -

Unless otherwise specified in the description of a particular function, if a built-in function or constructor is given fewer - arguments than the function is specified to require, the function or constructor shall behave exactly as if it had been given - sufficient additional arguments, each such argument being the undefined value. Such missing arguments are considered to - be “not present” and may be identified in that manner by specification algorithms.

- -

Unless otherwise specified in the description of a particular function, if a built-in function or constructor described is - given more arguments than the function is specified to allow, the extra arguments are evaluated by the call and then ignored by - the function. However, an implementation may define implementation specific behaviour relating to such arguments as long as the - behaviour is not the throwing of a TypeError exception that is predicated simply on the presence of an extra - argument.

- -
-

NOTE Implementations that add additional capabilities to the set of built-in functions are - encouraged to do so by adding new functions rather than adding new parameters to existing functions.

-
- -

Unless otherwise specified every built-in function and every built-in constructor has the Function prototype object, which is - the initial value of the expression Function.prototype (19.2.3), as the value of its [[Prototype]] internal slot.

- -

Unless otherwise specified every built-in prototype object has the Object prototype object, which is the initial value of the - expression Object.prototype (19.1.3), as the value of - its [[Prototype]] internal slot, except the Object prototype - object itself.

- -

Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method unless - otherwise specified in the description of a particular function.

- -

Unless otherwise specified, every built-in function defined in clauses 18 through 26 are created as if by calling the CreateBuiltinFunction abstract operation (9.3.1).

- -

Every built-in Function object, including constructors, has a length property whose value is an integer. Unless - otherwise specified, this value is equal to the largest number of named arguments shown in the subclause headings for the - function description, including optional parameters. However, rest parameters shown using the form “...name” are not - included in the default argument count.

- -
-

NOTE For example, the Function object that is the initial value of the slice property - of the String prototype object is described under the subclause heading “String.prototype.slice (start, end)” which shows the two named arguments start - and end; therefore the value of the length property of that Function object is 2.

-
- -

Unless otherwise specified, the length property of a built-in Function object has the attributes - { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -

Every built-in Function object, including constructors, that is not identified as an anonymous function has a - name property whose value is a String. Unless otherwise specified, this value is the name that is given to the - function in this specification. For functions that are specified as properties of objects, the name value is the property name - string used to access the function. Functions that are specified as get or set accessor functions of built-in properties have - "get " or "set " prepended to the property name string. The value of the name property - is explicitly specified for each built-in functions whose property key is a symbol value.

- -

Unless otherwise specified, the name property of a built-in Function object, if it exists, has the attributes - { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -

Every other data property described in clauses 18 through 26 has the attributes { [[Writable]]: true, [[Enumerable]]: - false, [[Configurable]]: true } unless otherwise specified.

- -

Every accessor property described in clauses 18 through 26 has the attributes {[[Enumerable]]: false, - [[Configurable]]: true } unless otherwise specified. If only a get accessor function is described, the set accessor - function is the default value, undefined. If only a set accessor is function is described the get accessor is the - default value, undefined.

-
- -
-
-

18 The Global - Object

- -

The unique global object is created before control enters any execution - context.

- -

The global object does not have a [[Construct]] internal method; it is not possible to use the global object as a - constructor with the new operator.

- -

The global object does not have a [[Call]] internal method; it is not possible to invoke the global object as a - function.

- -

The value of the [[Prototype]] internal slot of the global - object is implementation-dependent.

- -

In addition to the properties defined in this specification the global object may have additional host defined properties. - This may include a property whose value is the global object itself; for example, in the HTML document object model the - window property of the global object is the global object itself.

-
- -
-
-

18.1 Value Properties of the Global Object

-
- -
-

18.1.1 Infinity

- -

The value of Infinity is +∞ (see - 6.1.6). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

18.1.2 NaN

- -

The value of NaN is NaN (see 6.1.6). This - property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false - }.

-
- -
-

18.1.3 - undefined

- -

The value of undefined is undefined (see - 6.1.1). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
-
- -
-
-

18.2 Function Properties of the Global Object

-
- -
-
-

18.2.1 eval - (x)

- -

When the eval function is called with one argument x, the following steps are taken:

- -
    -
  1. If Type(x) is not String, return x.
    2. -
  2. Let script be the ECMAScript code that is the result of parsing x, interpreted as UTF-16 encoded - Unicode text as described in 10.1.1, for the goal symbol - Script. If the parse fails or any early errors are detected, throw a SyntaxError exception (but see also clause 16).
    3. -
  3. If script Contains ScriptBody is false, return undefined.
    4. -
  4. Let strictScript be IsStrict of script.
    5. -
  5. If this is a direct call to eval (18.2.1.1), let direct be - true, otherwise let direct be false.
    6. -
  6. If direct is true and the code that made the direct call to eval is strict code, then let strictCaller be true. Otherwise, let - strictCaller be false.
    7. -
  7. Let ctx be the running execution context. If direct is - true ctx will be the execution context that performed the direct - eval. If direct is false ctx will be the execution - context for the invocation of the eval function.
    8. -
  8. Let evalRealm be ctx’s Realm.
    9. -
  9. If direct is false and strictScript is false, then -
      -
    1. Return the result of ScriptEvaluation for script with arguments evalRealm and true.
      2. -
    -
    10. -
  10. If direct is true, strictScript is false, strictCaller is false, and - ctx’s LexicalEnvironment is the same as - evalRealm.[[globalEnv]], then -
      -
    1. Return the result of ScriptEvaluation for script with arguments evalRealm and true.
      2. -
    -
    11. -
  11. If direct is true, then -
      -
    1. If the code that made the direct call to eval is function code and ValidInFunction of script is - false, then throw a SyntaxError exception.
      2. -
    2. If the code that made the direct call to eval is module code and ValidInModule of script is false, - then throw a SyntaxError exception.
      3. -
    -
    12. -
  12. If direct is true, then -
      -
    1. Let lexEnv be ctx’s LexicalEnvironment.
      2. -
    2. Let varEnv be ctx’s VariableEnvironment.
      3. -
    -
    13. -
  13. Else, -
      -
    1. Let lexEnv be evalRealm.[[globalEnv]].
      2. -
    2. Let varEnv be evalRealm.[[globalEnv]].
      3. -
    -
    14. -
  14. If strictScript is true or if direct is true and strictCaller is true , - then -
      -
    1. Let strictVarEnv be NewDeclarativeEnvironment(lexEnv).
      2. -
    2. Let lexEnv be strictVarEnv.
      3. -
    3. Let varEnv be strictVarEnv.
      4. -
    -
    15. -
  15. Let status be the result of performing Eval Declaration Instantiation as described in 18.2.1.2 with script, varEnv, and lexEnv.
    16. -
  16. ReturnIfAbrupt(status).
    17. -
  17. Let evalCxt be a new ECMAScript code execution context.
    18. -
  18. Set the evalCxt’s Realm to evalRealm.
    19. -
  19. Set the evalCxt’s VariableEnvironment to varEnv.
    20. -
  20. Set the evalCxt’s LexicalEnvironment to lexEnv.
    21. -
  21. If there is a currently running execution context, suspend it.
    22. -
  22. Push evalCxt on to the execution context stack; evalCxt is now - the running execution context.
    23. -
  23. Let result be the result of evaluating script.
    24. -
  24. Suspend evalCxt and remove it from the execution context stack.
    25. -
  25. Resume the context that is now on the top of the execution context stack as the running execution context.
    26. -
  26. Return result.
    27. -
- -
-

NOTE The eval code cannot instantiate variable or function bindings in the variable - environment of the calling context that invoked the eval if either the code of the calling context or the eval code is - strict code. Instead such bindings are instantiated in a new VariableEnvironment that is only accessible to the eval code.

-
-
- -
-

18.2.1.1 Direct Call to Eval

- -

A direct call to the eval function is one that is expressed as a CallExpression that meets all - of the following conditions:

- -
    -
  • -

    The Reference that is the result of evaluating the MemberExpression - in the CallExpression will always have an environment record as its base value and its referenced name is "eval".

    -
    • - -
  • -

    The result of calling the abstract operation GetValue with that Reference as the argument is the standard built-in function defined in 18.2.1.

    -
    • -
-
- -
-

18.2.1.2 Eval Declaration Instantiation

-
-
- -
-

18.2.2 - isFinite (number)

- -

Returns false if the argument coerces to NaN, +∞, or −∞, and otherwise - returns true.

- -
    -
  1. Let num be ToNumber(number).
    2. -
  2. ReturnIfAbrupt(num).
    3. -
  3. If num is NaN, +∞, or −∞, return false.
    4. -
  4. Otherwise, return true.
    5. -
-
- -
-

18.2.3 isNaN - (number)

- -

Returns true if the argument coerces to NaN, and otherwise returns false.

- -
    -
  1. Let num be ToNumber(number).
    2. -
  2. ReturnIfAbrupt(num).
    3. -
  3. If num is NaN, return true.
    4. -
  4. Otherwise, return false.
    5. -
- -
-

NOTE A reliable way for ECMAScript code to test if a value X is a NaN is an - expression of the form X !== X. The result will be true if and only if X is a - NaN.

-
-
- -
-

18.2.4 - parseFloat (string)

- -

The parseFloat function produces a Number value dictated by interpretation of the contents of the - string argument as a decimal literal.

- -

When the parseFloat function is called, the following steps are taken:

- -
    -
  1. Let inputString be ToString(string).
    2. -
  2. ReturnIfAbrupt(inputString).
    3. -
  3. Let trimmedString be a substring of inputString consisting of the leftmost character that is not a - StrWhiteSpaceChar and all characters to the right of that character. (In other words, remove leading white - space.) If inputString does not contain any such characters, let trimmedString be the empty string.
    4. -
  4. If neither trimmedString nor any prefix of trimmedString satisfies the syntax of a - StrDecimalLiteral (see 7.1.3.1), return NaN.
    5. -
  5. Let numberString be the longest prefix of trimmedString, which might be trimmedString itself, - that satisfies the syntax of a StrDecimalLiteral.
    6. -
  6. Return the Number value for the MV of numberString.
    7. -
- -
-

NOTE parseFloat may interpret only a leading portion of string as a Number - value; it ignores any characters that cannot be interpreted as part of the notation of an decimal literal, and no - indication is given that any such characters were ignored.

-
-
- -
-

18.2.5 - parseInt (string , radix)

- -

The parseInt function produces an integer value dictated by interpretation of the contents of the - string argument according to the specified radix. Leading white space in string is ignored. - If radix is undefined or 0, it is assumed to be 10 - except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is - assumed. If radix is 16, the number may also optionally begin - with the character pairs 0x or 0X.

- -

When the parseInt function is called, the following steps are taken:

- -
    -
  1. Let inputString be ToString(string).
    2. -
  2. ReturnIfAbrupt(string).
    3. -
  3. Let S be a newly created substring of inputString consisting of the first character that is not a - StrWhiteSpaceChar and all characters following that character. (In other words, remove leading white space.) If - inputString does not contain any such characters, let S be the empty string.
    4. -
  4. Let sign be 1.
    5. -
  5. If S is not empty and the first character of S is a minus sign -, let sign be - −1.
    6. -
  6. If S is not empty and the first character of S is a plus sign + or a minus sign -, then - remove the first character from S.
    7. -
  7. Let R = ToInt32(radix).
    8. -
  8. ReturnIfAbrupt(R).
    9. -
  9. Let stripPrefix be true.
    10. -
  10. If R ≠ 0, then -
      -
    1. If R < 2 or R > 36, then return NaN.
      2. -
    2. If R ≠ 16, let stripPrefix be false.
      3. -
    -
    11. -
  11. Else R = 0, -
      -
    1. Let R = 10.
      2. -
    -
    12. -
  12. If stripPrefix is true, then -
      -
    1. If the length of S is at least 2 and the first two characters of S are either - “0x” or “0X”, then remove the first two characters from S and let - R = 16.
      2. -
    -
    13. -
  13. If S contains any character that is not a radix-R digit, then let Z be the substring of S - consisting of all characters before the first such character; otherwise, let Z be S.
    14. -
  14. If Z is empty, return NaN.
    15. -
  15. Let mathInt be the mathematical integer value that is represented by Z in radix-R notation, using - the letters A-Z and a-z for digits with values 10 through 35. (However, if R is 10 - and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a - 0 digit, at the option of the implementation; and if R is not 2, 4, 8, 10, 16, or 32, then - mathInt may be an implementation-dependent approximation to the mathematical integer value that is represented - by Z in radix-R notation.)
    16. -
  16. Let number be the Number value for mathInt.
    17. -
  17. Return sign × number.
    18. -
- -
-

NOTE parseInt may interpret only a leading portion of string as an integer - value; it ignores any characters that cannot be interpreted as part of the notation of an integer, and no indication is - given that any such characters were ignored.

-
-
- -
-
-

18.2.6 URI Handling Functions

- -

Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files) and transport - protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any - support for using URIs except for functions that encode and decode URIs as described in 18.2.6.2, 18.2.6.3, 18.2.6.4 and 18.2.6.5

- -
-

NOTE Many implementations of ECMAScript provide additional functions and methods that - manipulate web pages; these functions are beyond the scope of this standard.

-
-
- -
-
-

18.2.6.1 URI Syntax and Semantics

- -

A URI is composed of a sequence of components separated by component separators. The general form is:

- -
Scheme : First / Second ; Third ? Fourth
- -

where the italicized names represent components and “:”, “/”, - “;” and “?” are reserved characters used as separators. The - encodeURI and decodeURI functions are intended to work with complete URIs; they assume that - any reserved characters in the URI are intended to have special meaning and so are not encoded. The - encodeURIComponent and decodeURIComponent functions are intended to work with the individual - component parts of a URI; they assume that any reserved characters represent text and so must be encoded so that they - are not interpreted as reserved characters when the component is part of a complete URI.

- -

The following lexical grammar specifies the form of encoded URIs.

- -

Syntax

- -
-
uri :::
-
uriCharactersopt
-
- -
-
uriCharacters :::
-
uriCharacter uriCharactersopt
-
- -
-
uriCharacter :::
-
uriReserved
-
uriUnescaped
-
uriEscaped
-
- -
-
uriReserved ::: one of
-
; / ? : @ & = + $ ,
-
- -
-
uriUnescaped :::
-
uriAlpha
-
DecimalDigit
-
uriMark
-
- -
-
uriEscaped :::
-
% HexDigit HexDigit
-
- -
-
uriAlpha ::: one of
-
a b c d e f g h i j k l m n o p q r s t u v w x y z
-
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
-
- -
-
uriMark ::: one of
-
- _ . ! ~ * ' ( )
-
- -
-

NOTE The above syntax is based upon RFC 2396 and does not reflect changes introduced by the - more recent RFC 3986.

-
- -

Runtime Semantics

- -

When a character to be included in a URI is not listed above or is not intended to have the special meaning sometimes - given to the reserved characters, that character must be encoded. The character is transformed into its UTF-8 encoding, - with surrogate pairs first converted from UTF-16 to the corresponding code point value. (Note that for code units in the - range [0,127] this results in a single octet with the same value.) The resulting sequence of octets is then transformed - into a String with each octet represented by an escape sequence of the form “%xx”.

-
- -
-

18.2.6.1.1 - Runtime Semantics: Encode Abstract Operation

- -

The encoding and escaping process is described by the abstract operation Encode taking two String arguments - string and unescapedSet.

- -
    -
  1. Let strLen be the number of characters in string.
    2. -
  2. Let R be the empty String.
    3. -
  3. Let k be 0.
    4. -
  4. Repeat -
      -
    1. If k equals strLen, return R.
      2. -
    2. Let C be the character at position k within string.
      3. -
    3. If C is in unescapedSet, then -
        -
      1. Let S be a String containing only the character C.
        2. -
      2. Let R be a new String value computed by concatenating the previous value of R and - S.
        3. -
      -
      4. -
    4. Else C is not in unescapedSet, -
        -
      1. If the code unit value of C is not less than 0xDC00 and not greater than 0xDFFF, throw a URIError exception.
        2. -
      2. If the code unit value of C is less than 0xD800 or greater than 0xDBFF, then -
          -
        1. Let V be the code unit value of C.
          2. -
        -
        3. -
      3. Else, -
          -
        1. Increase k by 1.
          2. -
        2. If k equals strLen, throw a URIError exception.
          3. -
        3. Let kChar be the code unit value of the character at position k within - string.
          4. -
        4. If kChar is less than 0xDC00 or greater than 0xDFFF, throw a URIError exception.
          5. -
        5. Let V be (((the code unit value of C) – 0xD800) × 0x400 + (kChar - – 0xDC00) + 0x10000).
          6. -
        -
        4. -
      4. Let Octets be the array of octets resulting by applying the UTF-8 transformation to V, and - let L be the array size.
        5. -
      5. Let j be 0.
        6. -
      6. Repeat, while j < L -
          -
        1. Let jOctet be the value at position j within Octets.
          2. -
        2. Let S be a String containing three characters “%XY” where XY - are two uppercase hexadecimal digits encoding the value of jOctet.
          3. -
        3. Let R be a new String value computed by concatenating the previous value of R and - S.
          4. -
        4. Increase j by 1.
          5. -
        -
        7. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    5. -
-
- -
-

18.2.6.1.2 - Runtime Semantics: Decode Abstract Operation

- -

The unescaping and decoding process is described by the abstract operation Decode taking two String arguments - string and reservedSet.

- -
    -
  1. Let strLen be the number of characters in string.
    2. -
  2. Let R be the empty String.
    3. -
  3. Let k be 0.
    4. -
  4. Repeat -
      -
    1. If k equals strLen, return R.
      2. -
    2. Let C be the character at position k within string.
      3. -
    3. If C is not ‘%’, then -
        -
      1. Let S be the String containing only the character C.
        2. -
      -
      4. -
    4. Else C is ‘%’, -
        -
      1. Let start be k.
        2. -
      2. If k + 2 is greater than or equal to strLen, throw a URIError exception.
        3. -
      3. If the characters at position (k+1) and (k + 2) within string do not represent - hexadecimal digits, throw a URIError exception.
        4. -
      4. Let B be the 8-bit value represented by the two hexadecimal digits at position (k + 1) and - (k + 2).
        5. -
      5. Increment k by 2.
        6. -
      6. If the most significant bit in B is 0, then -
          -
        1. Let C be the character with code unit value B.
          2. -
        2. If C is not in reservedSet, then -
            -
          1. Let S be the String containing only the character C.
            2. -
          -
          3. -
        3. Else C is in reservedSet, -
            -
          1. Let S be the substring of string from position start to position k - included.
            2. -
          -
          4. -
        -
        7. -
      7. Else the most significant bit in B is 1, -
          -
        1. Let n be the smallest nonnegative integer such that (B << n) & 0x80 is - equal to 0.
          2. -
        2. If n equals 1 or n is greater than 4, throw a URIError exception.
          3. -
        3. Let Octets be an array of 8-bit integers of size n.
          4. -
        4. Put B into Octets at position 0.
          5. -
        5. If k + (3 × (n – 1)) is greater than or equal to strLen, throw a - URIError - exception.
          6. -
        6. Let j be 1.
          7. -
        7. Repeat, while j < n -
            -
          1. Increment k by 1.
            2. -
          2. If the character at position k within string is not "%″, throw a - URIError - exception.
            3. -
          3. If the characters at position (k +1) and (k + 2) within string do not - represent hexadecimal digits, throw a URIError exception.
            4. -
          4. Let B be the 8-bit value represented by the two hexadecimal digits at position (k + - 1) and (k + 2).
            5. -
          5. If the two most significant bits in B are not 10, throw a URIError exception.
            6. -
          6. Increment k by 2.
            7. -
          7. Put B into Octets at position j.
            8. -
          8. Increment j by 1.
            9. -
          -
          8. -
        8. Let V be the value obtained by applying the UTF-8 transformation to Octets, that is, - from an array of octets into a 21-bit value. If Octets does not contain a valid UTF-8 encoding - of a Unicode code point throw a URIError exception.
          9. -
        9. If V < 0x10000, then -
            -
          1. Let C be the character with code unit value V.
            2. -
          2. If C is not in reservedSet, then -
              -
            1. Let S be the String containing only the character C.
              2. -
            -
            3. -
          3. Else C is in reservedSet, -
              -
            1. Let S be the substring of string from position start to position k - included.
              2. -
            -
            4. -
          -
          10. -
        10. Else V ≥ 0x10000, -
            -
          1. Let L be (((V – 0x10000) & 0x3FF) + 0xDC00).
            2. -
          2. Let H be ((((V – 0x10000) >> 10) & 0x3FF) + 0xD800).
            3. -
          3. Let S be the String containing the two characters with code unit values H and - L.
            4. -
          -
          11. -
        -
        8. -
      -
      5. -
    5. Let R be a new String value computed by concatenating the previous value of R and S.
      6. -
    6. Increase k by 1.
      7. -
    -
    5. -
- -
-

NOTE This syntax of Uniform Resource Identifiers is based upon RFC 2396 and does not - reflect the more recent RFC 3986 which replaces RFC 2396. A formal description and implementation of UTF-8 is given - in RFC 3629.

-
- -

In UTF-8, characters are encoded using sequences of 1 to 6 octets. The only octet of a "sequence" of one has the - higher-order bit set to 0, the remaining 7 bits being used to encode the character value. In a sequence of n octets, - n>1, the initial octet has the n higher-order bits set to 1, followed by a bit set to 0. The remaining bits of that - octet contain bits from the value of the character to be encoded. The following octets all have the higher-order bit set - to 1 and the following bit set to 0, leaving 6 bits in each to contain bits from the character to be encoded. The - possible UTF-8 encodings of ECMAScript characters are specified in Table 38.

- -
-
Table 38 — UTF-8 Encodings
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Code Unit ValueRepresentation1st Octet2nd Octet3rd Octet4th Octet
0x0000 - 0x007F00000000 0zzzzzzz0zzzzzzz
0x0080 - 0x07FF00000yyy yyzzzzzz110yyyyy10zzzzzz
0x0800 - 0xD7FFxxxxyyyy yyzzzzzz1110xxxx10yyyyyy10zzzzzz
-

0xD800 - 0xDBFF

- -

followed by

- -

0xDC00 – 0xDFFF

- 		-

110110vv vvwwwwxx

- -

followed by

- -

110111yy yyzzzzzz

- 		11110uuu10uuwwww10xxyyyy10zzzzzz
-

0xD800 - 0xDBFF

- -

not followed by

- -

0xDC00 – 0xDFFF

- 		causes URIError
0xDC00 – 0xDFFFcauses URIError
0xE000 - 0xFFFFxxxxyyyy yyzzzzzz1110xxxx10yyyyyy10zzzzzz
-
- -

Where

- -

uuuuu = vvvv + 1

- -

to account for the addition of 0x10000 as in Surrogates, section 3.7, of the Unicode Standard.

- -

The range of code unit values 0xD800-0xDFFF is used to encode surrogate pairs; the above transformation combines a - UTF-16 surrogate pair into a UTF-32 representation and encodes the resulting 21-bit value in UTF-8. Decoding - reconstructs the surrogate pair.

- -

RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid sequence C0 80 must not - decode into the character U+0000. Implementations of the Decode algorithm are required to throw a URIError when encountering such invalid - sequences.

-
-
- -
-

18.2.6.2 decodeURI (encodedURI)

- -

The decodeURI function computes a new version of a URI in which each escape sequence and UTF-8 encoding of - the sort that might be introduced by the encodeURI function is replaced with the character that it - represents. Escape sequences that could not have been introduced by encodeURI are not replaced.

- -

When the decodeURI function is called with one argument encodedURI, the following steps are - taken:

- -
    -
  1. Let uriString be ToString(encodedURI).
    2. -
  2. ReturnIfAbrupt(uriString).
    3. -
  3. Let reservedURISet be a String containing one instance of each character valid in uriReserved plus - “#”.
    4. -
  4. Return the result of calling Decode(uriString, reservedURISet)
    5. -
- -
-

NOTE The character “#” is not decoded from escape sequences even - though it is not a reserved URI character.

-
-
- -
-

18.2.6.3 decodeURIComponent (encodedURIComponent)

- -

The decodeURIComponent function computes a new version of a URI in which each escape sequence and UTF-8 - encoding of the sort that might be introduced by the encodeURIComponent function is replaced with the - character that it represents.

- -

When the decodeURIComponent function is called with one argument encodedURIComponent, the - following steps are taken:

- -
    -
  1. Let componentString be ToString(encodedURIComponent).
    2. -
  2. ReturnIfAbrupt(componentString).
    3. -
  3. Let reservedURIComponentSet be the empty String.
    4. -
  4. Return Decode(componentString, reservedURIComponentSet)
    5. -
-
- -
-

18.2.6.4 - encodeURI (uri)

- -

The encodeURI function computes a new version of a URI in which each instance of certain characters is - replaced by one, two, three, or four escape sequences representing the UTF-8 encoding of the character.

- -

When the encodeURI function is called with one argument uri, the following steps - are taken:

- -
    -
  1. Let uriString be ToString(uri).
    2. -
  2. ReturnIfAbrupt(uriString).
    3. -
  3. Let unescapedURISet be a String containing one instance of each character valid in uriReserved and - uriUnescaped plus "#".
    4. -
  4. Return Encode(uriString, unescapedURISet)
    5. -
- -
-

NOTE The character "#" is not encoded to an escape sequence even though it is not a reserved or - unescaped URI character.

-
-
- -
-

18.2.6.5 encodeURIComponent (uriComponent)

- -

The encodeURIComponent function computes a new version of a URI in which each instance of certain - characters is replaced by one, two, three, or four escape sequences representing the UTF-8 encoding of the character.

- -

When the encodeURIComponent function is called with one argument uriComponent, the - following steps are taken:

- -
    -
  1. Let componentString be ToString(uriComponent).
    2. -
  2. ReturnIfAbrupt(componentString).
    3. -
  3. Let unescapedURIComponentSet be a String containing one instance of each character valid in - uriUnescaped.
    4. -
  4. Return Encode(componentString, unescapedURIComponentSet)
    5. -
-
-
-
- -
-
-

18.3 Constructor Properties of the Global Object

-
- -
-

18.3.1 Array ( . . . )

- -

See 22.1.1.

-
- -
-

18.3.2 ArrayBuffer ( . . . )

- -

See 24.1.2.

-
- -
-

18.3.3 Boolean ( . . . )

- -

See 19.3.1.

-
- -
-

18.3.4 DataView ( . . . )

- -

See 24.2.2.

-
- -
-

18.3.5 Date ( . . . )

- -

See 20.3.2.

-
- -
-

18.3.6 Error ( . . . )

- -

See 19.5.1.

-
- -
-

18.3.7 EvalError ( . . . )

- -

See 19.5.5.1.

-
- -
-

18.3.8 - Float32Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.9 - Float64Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.10 Function ( . . . )

- -

See 19.2.1.

-
- -
-

18.3.11 Int8Array - ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.12 - Int16Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.13 - Int32Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.14 Map ( . . . - )

- -

See 23.1.1.

-
- -
-

18.3.15 Number ( . . . )

- -

See 20.1.1.

-
- -
-

18.3.16 Object ( . . . )

- -

See 19.1.1.

-
- -
-

18.3.17 RangeError ( . . . )

- -

See 19.5.5.2.

-
- -
-

18.3.18 ReferenceError ( . . . )

- -

See 19.5.5.3.

-
- -
-

18.3.19 RegExp ( . . . )

- -

See 21.2.4.

-
- -
-

18.3.20 Set ( . . . - )

- -

See 23.2.1.

-
- -
-

18.3.21 String ( . . . )

- -

See 21.1.1.

-
- -
-

18.3.22 Symbol ( . . . )

- -

See 19.4.1.

-
- -
-

18.3.23 SyntaxError ( . . . )

- -

See 19.5.5.4.

-
- -
-

18.3.24 TypeError ( . . . )

- -

See 19.5.5.5.

-
- -
-

18.3.25 - Uint8Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.26 - Uint8ClampedArray ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.27 - Uint16Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.28 - Uint32Array ( . . . )

- -

See 22.2.4.

-
- -
-

18.3.29 URIError ( . . . )

- -

See 19.5.5.6.

-
- -
-

18.3.30 WeakMap ( . . . )

- -

See 23.3.1.

-
- -
-

18.3.31 WeakSet ( . . . )

- -

See 23.4.

-
-
- -
-
-

18.4 Other Properties of the Global Object

-
- -
-

18.4.1 JSON

- -

See 24.3.

-
- -
-

18.4.2 Math

- -

See 20.2.

-
- -
-

18.4.3 Proxy ( . . . )

- -

See 26.5.1.

-
- -
-

18.4.4 Reflect

- -

See 26.1.

-
- -
-

18.4.5 System

- -

See 26.4.

-
-
-
- -
-
-

19 Fundamental - Objects

-
- -
-
-

19.1 Object - Objects

-
- -
-
-

19.1.1 - The Object Constructor

- -

The Object constructor is the %Object% intrinsic object and the initial value of the Object property of - the global object. When Object is called as a function rather than as a constructor, it performs a type - conversion.

- -

The Object constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration.

- -
-

NOTE Subclass constructors that inherit from the Object constructor typically should not - include a super call to Object as it performs no initialization action on its - this value and does not return its this value as its value.

-
-
- -
-

19.1.1.1 - Object ( [ value ] )

- -

When Object function is called with optional argument value, the following steps are taken:

- -
    -
  1. If value is null, undefined or not supplied, return ObjectCreate(%ObjectPrototype%).
    2. -
  2. Return ToObject(value).
    3. -
-
- -
-

19.1.1.2 new Object ( ...argumentsList )

- -

When Object is called as part of a new expression , it creates a new object:

- -
    -
  1. Let F be the Object function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of calling the [[Call]] internal method of F, providing undefined and - argumentsList as the arguments.
    4. -
- -

The above steps defined the [[Construct]] internal method of the Object constructor. Object may not be implemented as - an ECMAScript function object because this definition differs from the - definition of [[Construct]] used by ECMAScript function objects.

-
-
- -
-
-

19.1.2 Properties of the Object Constructor

- -

The value of the [[Prototype]] internal slot of the - Object constructor is the standard built-in Function prototype object.

- -

Besides the length property (whose value is 1), the Object constructor has the following - properties:

-
- -
-

19.1.2.1 - Object.assign ( target, ...sources )

- -

The assign function is used to copy the values of all of the enumerable own properties from one or more source - objects to a target object. When the assign function is called, the following steps are taken:

- -
    -
  1. Let to be ToObject(target).
    2. -
  2. ReturnIfAbrupt(to).
    3. -
  3. If fewer than two arguments were passed, then return to.
    4. -
  4. Let sources be the List of argument vales starting with - the second argument.
    5. -
  5. For each element nextSource of sources, in ascending index order, -
      -
    1. Let from be ToObject(nextSource).
      2. -
    2. ReturnIfAbrupt(from).
      3. -
    3. Let keysArray be the result of calling the [[OwnPropertyKeys]] internal method of nextSource.
      4. -
    4. ReturnIfAbrupt(keysArray).
      5. -
    5. Let lenValue be Get(keysArray, "length").
      6. -
    6. Let len be ToLength(lenValue).
      7. -
    7. ReturnIfAbrupt(len).
      8. -
    8. Let nextIndex be 0.
      9. -
    9. Let pendingException be undefined.
      10. -
    10. Repeat while nextIndex < len, -
        -
      1. Let nextKey be Get(keysArray, ToString(nextIndex)).
        2. -
      2. ReturnIfAbrupt(nextKey).
        3. -
      3. Let desc be the result of calling the [[GetOwnProperty]] internal method of from with argument - nextKey.
        4. -
      4. If desc is an abrupt completion, then -
          -
        1. If pendingException is undefined, then set pendingException to desc.
          2. -
        -
        5. -
      5. Else if desc is not undefined and desc.[[Enumerable]] is true, then -
          -
        1. Let propValue be Get(from, nextKey).
          2. -
        2. If propValue is an abrupt completion, - then -
            -
          1. If pendingException is undefined, then set pendingException to - propValue.
            2. -
          -
          3. -
        3. else -
            -
          1. Let status be Put(to, nextKey, - propValue, true);
            2. -
          2. If status is an abrupt completion, - then -
              -
            1. If pendingException is undefined, then set pendingException to - status.
              2. -
            -
            3. -
          -
          4. -
        -
        6. -
      6. Increment nextIndex by 1.
        7. -
      -
      11. -
    11. If pendingException is not undefined, then return pendingException.
      12. -
    -
    6. -
  6. Return to.
    7. -
- -

The length property of the assign method is 2.

-
- -
-

19.1.2.2 - Object.create ( O [ , Properties ] )

- -

The create function creates a new object with a specified prototype. When the create function is called, - the following steps are taken:

- -
    -
  1. If Type(O) is not Object or Null throw a TypeError - exception.
    2. -
  2. Let obj be ObjectCreate(O).
    3. -
  3. If the argument Properties is present and not undefined, then -
      -
    1. Return the result of the abstract operation ObjectDefineProperties(obj, Properties).
      2. -
    -
    4. -
  4. Return obj.
    5. -
-
- -
-
-

19.1.2.3 Object.defineProperties ( O, Properties )

- -

The defineProperties function is used to add own properties and/or update the attributes of existing own - properties of an object. When the defineProperties function is called, the following steps are taken:

- -
    -
  1. Return the result of the abstract operation ObjectDefineProperties with - arguments O and Properties.
    2. -
-
- -
-

19.1.2.3.1 Runtime Semantics: ObjectDefineProperties Abstract Operation

- -

The abstract operation ObjectDefineProperties with arguments O and Properties performs the following - steps:

- -
    -
  1. If Type(O) is not Object throw a TypeError - exception.
    2. -
  2. Let props be ToObject(Properties).
    3. -
  3. Let names be a List containing the keys of each - enumerable own property of props.
    4. -
  4. Let descriptors be an empty List.
    5. -
  5. For each element P of names in list order, -
      -
    1. Let descObj be the result of Get( props, P).
      2. -
    2. ReturnIfAbrupt(descObj).
      3. -
    3. Let desc be the result of calling ToPropertyDescriptor with - descObj as the argument.
      4. -
    4. ReturnIfAbrupt(desc).
      5. -
    5. Append the pair (a two element List) consisting of - P and desc to the end of descriptors.
      6. -
    -
    6. -
  6. Let pendingException be undefined.
    7. -
  7. For each pair from descriptors in list order, -
      -
    1. Let P be the first element of pair.
      2. -
    2. Let desc be the second element of pair.
      3. -
    3. Let status be the result of DefinePropertyOrThrow(O,P, desc).
      4. -
    4. If status is an abrupt completion then, -
        -
      1. If pendingException is undefined, then set pendingException to status.
        2. -
      -
      5. -
    -
    8. -
  8. ReturnIfAbrupt(pendingException).
    9. -
  9. Return O.
    10. -
- -

If an implementation defines a specific order of enumeration for the for-in statement, that same enumeration order - must be used to order the list elements in step 3 of this algorithm.

- -
-

NOTE An exception in defining an individual property in step 7 does not terminate the - process of defining other properties. All valid property definitions are processed.

-
-
-
- -
-

19.1.2.4 Object.defineProperty ( O, P, Attributes )

- -

The defineProperty function is used to add an own property and/or update the attributes of an existing own - property of an object. When the defineProperty function is called, the following steps are taken:

- -
    -
  1. If Type(O) is not Object throw a TypeError - exception.
    2. -
  2. Let key be ToPropertyKey(P).
    3. -
  3. ReturnIfAbrupt(key).
    4. -
  4. Let desc be the result of calling ToPropertyDescriptor(Attributes).
    5. -
  5. ReturnIfAbrupt(desc).
    6. -
  6. Let success be the result of DefinePropertyOrThrow(O,key, - desc).
    7. -
  7. ReturnIfAbrupt(success).
    8. -
  8. Return O.
    9. -
-
- -
-

19.1.2.5 - Object.freeze ( O )

- -

When the freeze function is called, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return O.
    2. -
  2. Let status be the result of SetIntegrityLevel( O, - "frozen").
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. If status is false, throw a TypeError exception.
    5. -
  5. Return O.
    6. -
-
- -
-

19.1.2.6 Object.getOwnPropertyDescriptor ( O, P )

- -

When the getOwnPropertyDescriptor function is called, the following steps are taken:

- -
    -
  1. Let obj be ToObject(O).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(P).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. Let desc be the result of calling the [[GetOwnProperty]] internal method of obj with argument - key.
    6. -
  6. ReturnIfAbrupt(desc).
    7. -
  7. Return the result of calling FromPropertyDescriptor(desc).
    8. -
-
- -
-

19.1.2.7 Object.getOwnPropertyNames ( O )

- -

When the getOwnPropertyNames function is called, the following steps are taken:

- -
    -
  1. Return GetOwnPropertyKeys(O, String).
    2. -
-
- -
-
-

19.1.2.8 Object.getOwnPropertySymbols ( O )

- -

When the getOwnPropertySymbols function is called with argument O, the following steps are - taken:

- -
    -
  1. Return GetOwnPropertyKeys(O, Symbol).
    2. -
-
- -
-

19.1.2.8.1 GetOwnPropertyKeys ( O, Type ) Abstract Operation

- -

The abstract operation GetOwnPropertyKeys is called with arguments O and Type - where O is an Object and Type is one of the ECMAScript specification types String or - Symbol. The following steps are taken:

- -
    -
  1. Let obj be ToObject(O).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let keysArray be the result of calling the [[OwnPropertyKeys]] internal method of obj.
    4. -
  4. ReturnIfAbrupt(keysArray).
    5. -
  5. Let lenValue be Get(keysArray, "length").
    6. -
  6. Let len be ToLength(lenValue).
    7. -
  7. ReturnIfAbrupt(len).
    8. -
  8. Let nextIndex be 0.
    9. -
  9. Let nameList be a new empty List.
    10. -
  10. Repeat while nextIndex < len, -
      -
    1. Let nextKey be Get(keysArray, ToString(nextIndex)).
      2. -
    2. ReturnIfAbrupt(nextKey).
      3. -
    3. If Type(nextKey) is Type, then -
        -
      1. Append nextKey as the last element of nameList.
        2. -
      -
      4. -
    4. Increment nextIndex by 1.
      5. -
    -
    11. -
  11. Return CreateArrayFromList(nameList).
    12. -
-
-
- -
-

19.1.2.9 Object.getPrototypeOf ( O )

- -

When the getPrototypeOf function is called with argument O, the following steps are taken:

- -
    -
  1. Let obj be ToObject(O).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of calling the [[GetPrototypeOf]] internal method of obj.
    4. -
-
- -
-

19.1.2.10 - Object.is ( value1, value2 )

- -

When the is function is called with arguments value1 and value2 the following steps are - taken:

- -
    -
  1. Return SameValue(value1, value2).
    2. -
-
- -
-

19.1.2.11 Object.isExtensible ( O )

- -

When the isExtensible function is called with argument O, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return false.
    2. -
  2. Return the result of IsExtensible(O).
    3. -
-
- -
-

19.1.2.12 Object.isFrozen ( O )

- -

When the isFrozen function is called with argument O, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return true.
    2. -
  2. Return TestIntegrityLevel(O, "frozen").
    3. -
-
- -
-

19.1.2.13 Object.isSealed ( O )

- -

When the isSealed function is called with argument O, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return true.
    2. -
  2. Return TestIntegrityLevel(O, "sealed").
    3. -
-
- -
-

19.1.2.14 - Object.keys ( O )

- -

When the keys function is called with argument O, the following steps are taken:

- -
    -
  1. Let obj be ToObject(O).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let keysArray be the result of calling the [[OwnPropertyKeys]] internal method of obj.
    4. -
  4. ReturnIfAbrupt(keysArray).
    5. -
  5. Let lenValue be Get(keysArray, "length").
    6. -
  6. Let len be ToLength(lenValue).
    7. -
  7. ReturnIfAbrupt(len).
    8. -
  8. Let nextIndex be 0.
    9. -
  9. Let nameList be a new empty List.
    10. -
  10. Repeat while nextIndex < len, -
      -
    1. Let nextKey be Get(keysArray, ToString(nextIndex)).
      2. -
    2. ReturnIfAbrupt(nextKey).
      3. -
    3. If Type(nextKey) is String, then -
        -
      1. Let desc be the result of calling the [[GetOwnProperty]] internal method of O with argument - nextKey.
        2. -
      2. ReturnIfAbrupt(desc).
        3. -
      3. If desc is not undefined and desc.[[Enumerable]] is true, then -
          -
        1. Append nextKey as the last element of nameList.
          2. -
        -
        4. -
      -
      4. -
    4. Increment nextIndex by 1.
      5. -
    -
    11. -
  11. Return CreateArrayFromList(nameList).
    12. -
- -

If an implementation defines a specific order of enumeration for the for-in statement, the same order must be used for - the elements of the array returned in step 11.

-
- -
-

19.1.2.15 Object.preventExtensions ( O )

- -

When the preventExtensions function is called, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return O.
    2. -
  2. Let status be the result of calling the [[PreventExtensions]] internal method of O.
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. If status is false, throw a TypeError exception.
    5. -
  5. Return O.
    6. -
-
- -
-

19.1.2.16 Object.prototype

- -

The initial value of Object.prototype is the standard built-in Object prototype object (19.1.3).

- -

This property has the attributes {[[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.1.2.17 - Object.seal ( O )

- -

When the seal function is called, the following steps are taken:

- -
    -
  1. If Type(O) is not Object, return O.
    2. -
  2. Let status be the result of SetIntegrityLevel( O, - "sealed").
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. If status is false, throw a TypeError exception.
    5. -
  5. Return O.
    6. -
-
- -
-

19.1.2.18 Object.setPrototypeOf ( O, proto )

- -

When the setPrototypeOf function is called with arguments O and proto, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(O).
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. If Type(proto) is neither Object nor Null, then throw a - TypeError exception.
    4. -
  4. If Type(O) is not Object, then return O.
    5. -
  5. Let status be the result of calling the [[SetPrototypeOf]] internal method of O with argument - proto.
    6. -
  6. ReturnIfAbrupt(status).
    7. -
  7. If status is false, then throw a TypeError exception.
    8. -
  8. Return O.
    9. -
-
-
- -
-
-

19.1.3 Properties of the Object Prototype Object

- -

The Object prototype object is an ordinary object.

- -

The value of the [[Prototype]] internal slot of the - Object prototype object is null and the initial value of the [[Extensible]] internal slot is true.

-
- -
-

19.1.3.1 Object.prototype.constructor

- -

The initial value of Object.prototype.constructor is the standard built-in Object - constructor.

-
- -
-

19.1.3.2 Object.prototype.hasOwnProperty ( V )

- -

When the hasOwnProperty method is called with argument V, the following steps are taken:

- -
    -
  1. Let P be ToPropertyKey(V).
    2. -
  2. ReturnIfAbrupt(P).
    3. -
  3. Let O be the result of calling ToObject passing the this value as the - argument.
    4. -
  4. ReturnIfAbrupt(O).
    5. -
  5. Return the result of HasOwnProperty(O, P).
    6. -
- -
-

NOTE The ordering of steps 1 and 3 is chosen to ensure that any exception that would have - been thrown by step 1 in previous editions of this specification will continue to be thrown even if the this - value is undefined or null.

-
-
- -
-

19.1.3.3 Object.prototype.isPrototypeOf ( V )

- -

When the isPrototypeOf method is called with argument V, the following steps are taken:

- -
    -
  1. If V is not an object, return false.
    2. -
  2. Let O be the result of calling ToObject passing the this value as the - argument.
    3. -
  3. ReturnIfAbrupt(O).
    4. -
  4. Repeat -
      -
    1. Let V be the result of calling the [[GetPrototypeOf]] internal method of V with no arguments.
      2. -
    2. if V is null, return false
      3. -
    3. If SameValue(O, V) is true, then return true.
      4. -
    -
    5. -
- -
-

NOTE The ordering of steps 1 and 2 preserves the behaviour specified by previous editions of - this specification for the case where V is not an object and the this value is undefined or null.

-
-
- -
-

19.1.3.4 Object.prototype.propertyIsEnumerable ( V )

- -

When the propertyIsEnumerable method is called with argument V, the following steps are - taken:

- -
    -
  1. Let P be ToPropertyKey(V).
    2. -
  2. ReturnIfAbrupt(P).
    3. -
  3. Let O be the result of calling ToObject passing the this value as the - argument.
    4. -
  4. ReturnIfAbrupt(O).
    5. -
  5. Let desc be the result of calling the [[GetOwnProperty]] internal method of O passing P as the - argument.
    6. -
  6. ReturnIfAbrupt(desc).
    7. -
  7. If desc is undefined, return false.
    8. -
  8. Return the value of desc.[[Enumerable]].
    9. -
- -
-

NOTE 1 This method does not consider objects in the prototype chain.

-
- -
-

NOTE 2 The ordering of steps 1 and 3 is chosen to ensure that any exception that would have - been thrown by step 1 in previous editions of this specification will continue to be thrown even if the this - value is undefined or null.

-
-
- -
-

19.1.3.5 Object.prototype.toLocaleString ( )

- -

When the toLocaleString method is called, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. Return the result of Invoke(O, "toString").
    3. -
- -
-

NOTE 1 This function is provided to give all Objects a generic toLocaleString - interface, even though not all may use it. Currently, Array, Number, and Date - provide their own locale-sensitive toLocaleString methods.

-
- -
-

NOTE 2 The first parameter to this function is likely to be used in a future version of this - standard; it is recommended that implementations do not use this parameter position for anything else.

-
-
- -
-

19.1.3.6 Object.prototype.toString ( )

- -

When the toString method is called, the following steps are taken:

- -
    -
  1. If the this value is undefined, return "[object Undefined]".
    2. -
  2. If the this value is null, return "[object Null]".
    3. -
  3. Let O be the result of calling ToObject passing the this value as the - argument.
    4. -
  4. If O is an exotic Array object, then let builtinTag be "Array".
    5. -
  5. Else, if O is an exotic String object, then let builtinTag be "String".
    6. -
  6. Else, if O has an [[ParameterMap]] internal - slot, then let builtinTag be "Arguments".
    7. -
  7. Else, if O has a [[Call]] internal method, then let builtinTag be "Function".
    8. -
  8. Else, if O has an [[ErrorData]] internal slot, - then let builtinTag be "Error".
    9. -
  9. Else, if O has a [[BooleanData]] internal slot, - then let builtinTag be "Boolean".
    10. -
  10. Else, if O has a [[NumberData]] internal slot, - then let builtinTag be "Number".
    11. -
  11. Else, if O has a [[DateValue]] internal slot, - then let builtinTag be "Date".
    12. -
  12. Else, if O has a [[RegExpMatcher]] internal - slot, then let builtinTag be "RegExp".
    13. -
  13. Else, let builtinTag be "Object".
    14. -
  14. Let hasTag be the result of HasProperty(O, @@toStringTag).
    15. -
  15. ReturnIfAbrupt(hasTag).
    16. -
  16. If hasTag is false, then let tag be builtinTag.
    17. -
  17. Else, -
      -
    1. Let tag be the result of Get(O, @@toStringTag).
      2. -
    2. If tag is an abrupt completion, let tag be - NormalCompletion("???").
      3. -
    3. Let tag be tag.[[value]].
      4. -
    4. If Type(tag) is not String, let tag be - "???".
      5. -
    5. If tag is any of "Arguments", "Array", "Boolean", - "Date", "Error", "Function", "Number", - "RegExp", or "String" and SameValue(tag, - builtinTag) is false, then let tag be the string value "~" concatenated with - the current value of tag.
      6. -
    -
    18. -
  18. Return the String value that is the result of concatenating the three Strings "[object ", tag, - and "]".
    19. -
- -
-

NOTE Historically, this function was occasionally used to access the string value of the - [[Class]] internal slot that was used in previous editions - of this specification as a nominal type tag for various built-in objects. The above definition of toString - preserves the ability to use it as a reliable test for those specific kinds of built-in objects but it does not provide - a reliable type testing mechanism for other kinds of built-in or program defined objects.

-
-
- -
-

19.1.3.7 Object.prototype.valueOf ( )

- -

When the valueOf method is called, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. Return O.
    3. -
-
-
- -
-

19.1.4 Properties of Object Instances

- -

Object instances have no special properties beyond those inherited from the Object prototype object.

-
-
- -
-
-

19.2 Function - Objects

-
- -
-
-

19.2.1 The Function Constructor

- -

The Function constructor is the %Function% intrinsic object and the initial value of the Function property - of the global object. When Function is called as a function rather than as a constructor, it creates and - initializes a new Function object. Thus the function call Function(…) is equivalent to - the object creation expression new Function(…) with the same arguments. However, if the - this value passed in the call is an Object with a [[Code]] internal slot whose value is undefined, it initializes the this value using the argument values. This permits - Function to be used both as factory method and to perform constructor instance initialization.

- -

Function may be subclassed and subclass constructors may perform a super invocation of the - Function constructor to initialize subclass instances. However, all syntactic forms for defining function - objects create instances of Function. There is no syntactic means to create instances of - Function subclasses except for the built-in Generator Function subclass.

-
- -
-

19.2.1.1 Function ( p1, p2, … , pn, body )

- -

The last argument specifies the body (executable code) of a function; any preceding arguments specify formal - parameters.

- -

When the Function function is called with some arguments p1, p2, … , - pn, body (where n might be 0, that is, - there are no “p” arguments, and where body might also not be provided), the following - steps are taken:

- -
    -
  1. Let argCount be the total number of arguments passed to this function invocation.
    2. -
  2. Let P be the empty String.
    3. -
  3. If argCount = 0, let bodyText be the empty String.
    4. -
  4. Else if argCount = 1, let bodyText be that argument.
    5. -
  5. Else argCount > 1, -
      -
    1. Let firstArg be the first argument.
      2. -
    2. Let P be ToString(firstArg).
      3. -
    3. ReturnIfAbrupt(P).
      4. -
    4. Let k be 2.
      5. -
    5. Repeat, while k < argCount -
        -
      1. Let nextArg be the k’th argument.
        2. -
      2. Let nextArgString be ToString(nextArg).
        3. -
      3. ReturnIfAbrupt(nextArgString).
        4. -
      4. Let P be the result of concatenating the previous value of P, the String "," (a - comma), and nextArgString.
        5. -
      5. Increase k by 1.
        6. -
      -
      6. -
    6. Let bodyText be the k’th argument.
      7. -
    -
    6. -
  6. Let bodyText be ToString(bodyText).
    7. -
  7. ReturnIfAbrupt(bodyText).
    8. -
  8. Let parameters be the result of parsing P, interpreted as UTF-16 encoded Unicode text as described in - 10.1.1, using FormalParameters as the goal symbol. - Throw a SyntaxError exception if the parse fails.
    9. -
  9. Let body be the result of parsing bodyText, interpreted as UTF-16 encoded Unicode text as described in - 10.1.1, using FunctionBody as the goal symbol. - Throw a SyntaxError exception if the parse fails or if any static semantics errors are detected.
    10. -
  10. If IsSimpleParameterList of parameters is false and any element of the BoundNames of parameters - also occurs in the VarDeclaredNames of body, then throw a SyntaxError exception.
    11. -
  11. If any element of the BoundNames of parameters also occurs in the LexicallyDeclaredNames of body, then - throw a SyntaxError exception.
    12. -
  12. If bodyText is strict mode code (see - 10.2.1) then let strict be true, else let strict be false.
    13. -
  13. Let scope be the Global Environment.
    14. -
  14. Let F be the this value.
    15. -
  15. If Type(F) is not Object or if F does not have a - [[Code]] internal slot or if the value of [[Code]] is - not undefined, then -
      -
    1. Let C be the function that is currently being evaluated.
      2. -
    2. Let proto be the result of GetPrototypeFromConstructor(C, - "%FunctionPrototype%").
      3. -
    3. ReturnIfAbrupt(proto).
      4. -
    4. Let F be FunctionAllocate(C, strict).
      5. -
    5. ReturnIfAbrupt(F).
      6. -
    -
    16. -
  16. If the value of F’s [[FunctionKind]] internal - slot is not "normal", then throw a TypeError exception.
    17. -
  17. Let isExtensible be IsExtensible(F).
    18. -
  18. ReturnIfAbrupt(isExtensible).
    19. -
  19. If isExtensible is false, then throw a TypeError exception.
    20. -
  20. Let status be FunctionInitialize(F, Normal, strict, parameters, body, scope).
    21. -
  21. ReturnIfAbrupt(status).
    22. -
  22. If ReferencesSuper of body is true or ReferencesSuper of parameters is true, then -
      -
    1. Perform MakeMethod(F, undefined, undefined).
      2. -
    -
    23. -
  23. Let status be the result of MakeConstructor with argument F.
    24. -
  24. ReturnIfAbrupt(status).
    25. -
  25. Let hasName be HasOwnProperty(F, "name").
    26. -
  26. ReturnIfAbrupt(hasName).
    27. -
  27. If hasName is false, then perform SetFunctionName(F, - "anonymous").
    28. -
  28. Return F.
    29. -
- -

The length property of the Funtion function is 1 (see - 19.2.2.1).

- -
-

NOTE 1 A prototype property is automatically created for every function created - using the Function constructor, to provide for the possibility that the function will be used as a - constructor.

-
- -
-

NOTE 2 It is permissible but not necessary to have one argument for each formal parameter to - be specified. For example, all three of the following expressions produce the same result:

- - 
new Function("a", "b", "c", "return a+b+c")
- 
new Function("a, b, c", "return a+b+c")
- 
new Function("a,b", "c", "return a+b+c")
-
-
- -
-

19.2.1.2 new Function ( ...argumentsList )

- -

When Function is called as part of a new expression, it initializes the newly created - object.

- -
    -
  1. Let F be the Function function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If Function is implemented as an ECMAScript function - object, its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

19.2.2 Properties of the Function Constructor

- -

The Function constructor is itself a built-in Function object. The value of the [[Prototype]] internal slot of the Function constructor is - %FunctionPrototype%, the intrinsic Function prototype object (19.2.3).

- -

The value of the [[Extensible]] internal slot of the - Function constructor is true.

- -

The Function constructor has the following properties:

-
- -
-

19.2.2.1 - Function.length

- -

This is a data property with a value of 1. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

19.2.2.2 Function.prototype

- -

The value of Function.prototype is %FunctionPrototype%, the intrinsic Function prototype object (19.2.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

-
- -
-

19.2.2.3 Function[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let proto be the result of GetPrototypeFromConstructor(F, - "%FunctionPrototype%").
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Return FunctionAllocate(proto, false).
    5. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE The Function @@create function passes false as the strict - parameter to FunctionAllocate. This causes the allocated ECMAScript function object to have the internal methods of a non-strict - function. The Function constructor may reset the functions [[Strict]] internal slot to true. It is up to the implementation - whether this also changes the internal methods.

-
-
-
- -
-
-

19.2.3 Properties of the Function Prototype Object

- -

The Function prototype object is itself a Built-in Function object. When invoked, it accepts any arguments and returns - undefined.

- -
-

NOTE The Function prototype object is specified to be a function object to ensure - compatibility with ECMAScript code that was created prior to the 6th Edition of this specification.

-
- -

The value of the [[Prototype]] internal slot of the - Function prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The initial value of the [[Extensible]] internal slot of the Function prototype object is - true.

- -

The Function prototype object does not have a prototype property.

- -

The value of The length property of the Function prototype object is 0.

- -

The value of the name property of the Function prototype object is the empty String.

-
- -
-

19.2.3.1 Function.prototype.apply ( thisArg, argArray )

- -

When the apply method is called on an object func with arguments thisArg and - argArray, the following steps are taken:

- -
    -
  1. If IsCallable(func) is false, then throw a TypeError - exception.
    2. -
  2. If argArray is null or undefined, then -
      -
    1. Return the result of calling the [[Call]] internal method of func, providing thisArg as - thisArgument and an empty List of arguments as - argumentsList.
      2. -
    -
    3. -
  3. Let argList be the result of CreateListFromArrayLike(argArray).
    4. -
  4. ReturnIfAbrupt(argList ).
    5. -
  5. Perform PrepareForTailCall().
    6. -
  6. Return the result of calling the [[Call]] internal method of func, providing thisArg as - thisArgument and argList as argumentsList.
    7. -
- -

The length property of the apply method is 2.

- -
-

NOTE The thisArg value is passed without modification as the this value. This is a - change from Edition 3, where an undefined or null thisArg is replaced with the global object and ToObject is applied to all other values and that result is passed as the this value. - Even though the thisArg is passed without modification, non-strict mode functions still perform these transfromations - upon entry to the function.

-
-
- -
-

19.2.3.2 Function.prototype.bind ( thisArg , ...args)

- -

When the bind is called with argument thisArg and zero or more args, it performs the - following steps:

- -
    -
  1. Let Target be the this value.
    2. -
  2. If IsCallable(Target) is false, throw a TypeError exception.
    3. -
  3. Let args be a new (possibly empty) List consisting of - all of the argument values provided after thisArg in order.
    4. -
  4. Let F be the result of the abstract operation BoundFunctionCreate with - arguments Target, thisArg, and args.
    5. -
  5. If Target has a [[BoundTargetFunction]] internal slot, then -
      -
    1. Let targetLen be the result of Get(Target, "length").
      2. -
    2. ReturnIfAbrupt(targetLen).
      3. -
    3. Let L be the larger of 0 and the result of targetLen minus the number of elements of - A.
      4. -
    -
    6. -
  6. Else let L be 0.
    7. -
  7. Call the [[DefineOwnProperty]] internal method of F with arguments "length" and - PropertyDescriptor {[[Value]]: L, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true}.
    8. -
  8. Let targetRealm be BoundFunctionTargetRealm(Target).
    9. -
  9. Perform the AddRestrictedFunctionProperties(F, - targetRealm).
    10. -
  10. Return F.
    11. -
- -

The length property of the bind method is 1.

- -
-

NOTE Function objects created using Function.prototype.bind are exotic objects. - They also do not have a prototype property.

-
-
- -
-

19.2.3.3 Function.prototype.call (thisArg , ...args)

- -

When the call method is called on an object func with argument, thisArg and zero or - more args, the following steps are taken:

- -
    -
  1. If IsCallable(func) is false, then throw a TypeError - exception.
    2. -
  2. Let argList be an empty List.
    3. -
  3. If this method was called with more than one argument then in left to right order starting with the second - argument append each argument as the last element of argList
    4. -
  4. Perform PrepareForTailCall().
    5. -
  5. Return the result of calling the [[Call]] internal method of func, providing thisArg as - thisArgument and argList as argumentsList.
    6. -
- -

The length property of the call method is 1.

- -
-

NOTE The thisArg value is passed without modification as the this value. This is a - change from Edition 3, where an undefined or null thisArg is replaced with the global object and ToObject is applied to all other values and that result is passed as the this value. - Even though the thisArg is passed without modification, non-strict mode functions still perform these transfromations - upon entry to the function.

-
-
- -
-

19.2.3.4 Function.prototype.constructor

- -

The initial value of Function.prototype.constructor is the intrinsic object %Function%.

-
- -
-

19.2.3.5 Function.prototype.toMethod (newHome [ , methodName ] )

- -

When the toMethod method is called on an object func with argument superBinding and - optional argument methodName the following steps are taken:

- -
    -
  1. If Type(newHome) is not Object, then throw a - TypeError exception.
    2. -
  2. If func is an ECMAScript function object or an exotic Built-in - function object, then -
      -
    1. If methodName is not undefined, then -
        -
      1. Let methodName be ToPropertyKey(methodName).
        2. -
      2. ReturnIfAbrupt(methodName).
        3. -
      -
      2. -
    2. Return CloneMethod(func, newHome, methodName).
      3. -
    -
    3. -
  3. If func is a Bound Function exotic object, then return BoundFunctionClone(func).
    4. -
  4. If func is any other exotic function object that supports the equivalent of the CloneMethod abstract operation, then return an appropriately cloned object.
    5. -
  5. Throw a TypeError exception.
    6. -
- -

The length property of the toMethod method is 1.

-
- -
-

19.2.3.6 Function.prototype.toString ( )

- -

An implementation-dependent String source code representation of the this object is returned. This - representation has the syntax of a FunctionDeclaration FunctionExpression, GeneratorDeclaration, GeneratorExpession, ClassDeclaration, - ClassExpression, ArrowFunction, MethodDefinition, or GeneratorMethod depending upon the actual - characteristics of the object. In particular that the use and placement of white space, line terminators, and - semicolons within the representation String is implementation-dependent.

- -

If the object was defined using ECMAScript code and the returned string representation is in the form of a FunctionDeclaration FunctionExpression, - GeneratorDeclaration, GeneratorExpession, ClassDeclaration, ClassExpression, or ArrowFunction - then the representation must be such that if the string is evaluated, using eval in a lexical context that is - equivalent to the lexical context used to create the original object, it will result in a new functionally equivalent - object. The returned source code must not mention freely any variables that were not mentioned freely by the original - function’s source code, even if these “extra” names were originally in scope. If the implementation - cannot produce a source code string that meets these criteria then it must return a string for which eval - will throw a SyntaxError exception.

- -

The toString function is not generic; it throws a TypeError exception if its this value does - not have a [[Call]] internal method. Therefore, it cannot be transferred to other kinds of objects for use as a - method.

-
- -
-

19.2.3.7 Function.prototype[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Return the result of calling OrdinaryCreateFromConstructor(F, - "%ObjectPrototype%").
    2. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE This is the default @@create method that is inherited by all ordinary constructor - functions that do not explicitly over-ride it.

-
-
- -
-

19.2.3.8 Function.prototype[@@hasInstance] ( V )

- -

When the @@hasInstance method of an object F is called with value V, the following steps are - taken:

- -
    -
  1. Let F be the this value.
    2. -
  2. Return the result of OrdinaryHasInstance(F, V).
    3. -
- -

The value of the name property of this function is "[Symbol.hasInstance]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: false }.

- -
-

NOTE This is the default implementation of @@hasInstance that most functions - inherit. @@hasInstance is called by the instanceof operator to deterimine whether a value is - an instance of a specific constructor. An expression such as

- - 
v instanceof F
- -

evaluates as

- - 
F[@@hasInstance](v)
- -

A constructor function can control which objects are recognized as its instances by instanceof by - exposing a different @@hasInstance method on the function.

- -

This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the - target function of a bound function.

-
-
-
- -
-
-

19.2.4 - Function Instances

- -

Every function instance is an ECMAScript function object and has the - internal slots listed in Table 26.

- -

Function instances that correspond to strict mode functions and function instances created using the Function.prototype.bind method (19.2.3.2) have properties named caller and - arguments that throw a TypeError exception. An ECMAScript implementation must not associate any - implementation specific behaviour with accesses of these properties from strict mode function code.

- -

The Function instances have the following properties:

-
- -
-

19.2.4.1 length

- -

The value of the length property is an integer that indicates the typical number of arguments expected by - the function. However, the language permits the function to be invoked with some other number of arguments. The behaviour - of a function when invoked on a number of arguments other than the number specified by its length property - depends on the function. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: true }.

-
- -
-

19.2.4.2 name

- -

The value of the name property is an String that is descriptive of the function. The name has no semantic - significance but is typically a variable or property name that is used to refer to the function at its point of definition - in ECMAScript code. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: true }.

- -

Anonymous functions objects that do not have a contextual name associated with them by this specification do not have a - name own property but inherit the name property of %FunctionPrototype%.

- -

Function objects created using Function.prototype.bind do not have a name property.

-
- -
-

19.2.4.3 prototype

- -

Function instances that can be used as a constructor have a prototype property. Whenever such a function - instance is created another ordinary object is also created and is the initial value of the function’s - prototype property. Unless otherwise specified, the value of the prototype property is used to initialize the - [[Prototype]] internal slot of a newly created ordinary - object before the Function object is invoked as a constructor for that newly created object.

- -

This property has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: - false }.

- -
-

NOTE Function objects created using Function.prototype.bind, or by evaluating a MethodDefinition (that - is not a GeneratorMethod) or an ArrowFunction grammar production do not have a prototype - property.

-
-
-
-
- -
-
-

19.3 Boolean - Objects

-
- -
-
-

19.3.1 - The Boolean Constructor

- -

The Boolean constructor is the %Boolean% intrinsic object and the initial value of the Boolean property of - the global object. When Boolean is called as a function rather than as a constructor, it performs a type - conversion. However, if the this value passed in the call is an Object with an uninitialized [[BooleanData]] internal slot, it initializes the this value using the - argument value. This permits Boolean to be used both to perform type conversion and to perform constructor - instance initialization.

- -

The Boolean constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - Boolean behaviour must include a super call to the Boolean constructor to - initialize the [[BooleanData]] state of subclass instances.

-
- -
-

19.3.1.1 Boolean ( value )

- -

When Boolean is called with argument value, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. Let b be ToBoolean(value).
    3. -
  3. If Type(O) is Object and O has a [[BooleanData]] - internal slot and the value of [[BooleanData]] is - undefined, then -
      -
    1. Set the value of O’s [[BooleanData]] internal slot to b.
      2. -
    2. Return O.
      3. -
    -
    4. -
  4. Return b.
    5. -
-
- -
-

19.3.1.2 new Boolean ( ...argumentsList )

- -

When Boolean is called as part of a new expression , it initializes a newly created object:

- -
    -
  1. Let F be the Boolean function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If Boolean is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

19.3.2 Properties of the Boolean Constructor

- -

The value of the [[Prototype]] internal slot of the - Boolean constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Boolean constructor has the following - properties:

-
- -
-

19.3.2.1 Boolean.prototype

- -

The initial value of Boolean.prototype is the Boolean prototype object (19.3.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.3.2.2 Boolean[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%BooleanPrototype%", ( [[BooleanData]]) ).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

- -
-

NOTE [[BooleanData]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the Boolean constructor. This flag value is never directly exposed to - ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

19.3.3 Properties of the Boolean Prototype Object

- -

The Boolean prototype object is an ordinary object. It is not a Boolean instance and does not have a [[BooleanData]] internal slot.

- -

The value of the [[Prototype]] internal slot of the - Boolean prototype object is the standard built-in Object prototype object (19.1.3).

- -

The abstract operation thisBooleanValue(value) performs the - following steps:

- -
    -
  1. If Type(value) is Boolean, return value.
    2. -
  2. If Type(value) is Object and value has a - [[BooleanData]] internal slot, then -
      -
    1. Let b be the value of value’s [[BooleanData]] internal slot.
      2. -
    2. If b is not undefined, then return b.
      3. -
    -
    3. -
  3. Throw a TypeError exception.
    4. -
-
- -
-

19.3.3.1 Boolean.prototype.constructor

- -

The initial value of Boolean.prototype.constructor is the built-in Boolean constructor.

-
- -
-

19.3.3.2 Boolean.prototype.toString ( )

- -

The following steps are taken:

- -
    -
  1. Let b be thisBooleanValue(this value).
    2. -
  2. ReturnIfAbrupt(b).
    3. -
  3. If b is true, then return "true"; else return "false".
    4. -
-
- -
-

19.3.3.3 Boolean.prototype.valueOf ( )

- -

The following steps are taken:

- -
    -
  1. Return thisBooleanValue(this value).
    2. -
-
-
- -
-

19.3.4 Properties of Boolean Instances

- -

Boolean instances are ordinary objects that inherit properties from the Boolean prototype object. Boolean instances have - a [[BooleanData]] internal slot. The [[BooleanData]] internal slot is the Boolean value represented by this Boolean - object.

-
-
- -
-
-

19.4 Symbol - Objects

-
- -
-
-

19.4.1 - The Symbol Constructor

- -

The Symbol constructor is the %Symbol% intrinsic object and the initial value of the Symbol property of - the global object. When Symbol is called as a function rather than as a constructor, it returns a new Symbol - value.

- -

The Symbol constructor is not intended to be used with the new operator or to be subclassed. - It may be used as the value of an extends clause of a class declaration but a super call to the - Symbol constructor will not initialize the state of subclass instances.

-
- -
-

19.4.1.1 Symbol ( [ description ] )

- -

When Symbol is called with optional argument description, the following steps are taken:

- -
    -
  1. If description is undefined, then let descString be undefined.
    2. -
  2. Else, let descString be ToString(description).
    3. -
  3. ReturnIfAbrupt(descString).
    4. -
  4. Return a new unique Symbol value whose [[Description]] value is descString.
    5. -
-
- -
-

19.4.1.2 new Symbol ( ...argumentsList )

- -

When Symbol is called as part of a new expression , it initializes a newly created object:

- -
    -
  1. Let F be the Symbol function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If Symbol is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

- -
-

NOTE Symbol has ordinary [[Construct]] behaviour but the definition of its @@create method - causes new Symbol to throw a TypeError exception.

-
-
-
- -
-
-

19.4.2 Properties of the Symbol Constructor

- -

The value of the [[Prototype]] internal slot of the - Symbol constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Symbol constructor has the following - properties:

-
- -
-

19.4.2.1 - Symbol.create

- -

The initial value of Symbol.create is the well known symbol @@create (Table 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.2 - Symbol.for ( key )

- -

When Symbol.for is called with argument key it performs the following steps:

- -
    -
  1. Let stringKey be ToString(key).
    2. -
  2. ReturnIfAbrupt(stringKey).
    3. -
  3. For each element e of the GlobalSymbolRegistry List, -
      -
    1. If SameValue(e.[[key]], stringKey) is true, then return - e.[[symbol]].
      2. -
    -
    4. -
  4. Assert: GlobalSymbolRegistry does not currently contain an entry for - stringKey.
    5. -
  5. Let newSymbol be a new unique Symbol value whose [[Description]] is stringKey.
    6. -
  6. Append the record { [[key]]: stringKey, [[symbol]]: newSymbol } to the GlobalSymbolRegistry List.
    7. -
  7. Return newSymbol.
    8. -
- -

The GlobalSymbolRegistry is a List that is globally available. - It is shared by all Code Realms. Prior to the evaluation of any ECMAScript code it is initialized as an empty List. Elements of the GlobalSymbolRegistry are Records with the - structure defined in Table 39.

- -
-
Table 39 — GlobalSymbolRegistry Record Fields
- - - - - - - - - - - - - - - - -
Field NameValueUsage
[[key]]A StringA string key used to globally identify a Symbol.
[[symbol]]A SymbolA symbol that can be retrieved from any Realm.
-
-
- -
-

19.4.2.3 Symbol.hasInstance

- -

The initial value of Symbol.hasInstance is the well known symbol @@hasInstance (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.4 Symbol.isConcatSpreadable

- -

The initial value of Symbol.isConcatSpreadable is the well known symbol @@isConcatSpreadable (Table 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.5 - Symbol.isRegExp

- -

The initial value of Symbol.isRegExp is the well known symbol @@isRegExp (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.6 - Symbol.iterator

- -

The initial value of Symbol.iterator is the well known symbol @@iterator (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.7 - Symbol.keyFor ( sym )

- -

When Symbol.keyFor is called with argument sym it performs the following steps:

- -
    -
  1. If Type(sym) is not Symbol, then throw a TypeError - exception.
    2. -
  2. For each element e of the GlobalSymbolRegistry List (see 19.4.2.2), -
      -
    1. If SameValue(e.[[symbol]], sym) is true, then return - e.[[key]].
      2. -
    -
    3. -
  3. Assert: GlobalSymbolRegistry does not currently contain an entry for - sym.
    4. -
  4. Return undefined.
    5. -
-
- -
-

19.4.2.8 Symbol.prototype

- -

The initial value of Symbol.prototype is the Symbol prototype object (19.4.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.9 Symbol.toPrimitive

- -

The initial value of Symbol.toPrimitive is the well known symbol @@toPrimitive (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.10 Symbol.toStringTag

- -

The initial value of Symbol.toStringTag is the well known symbol @@toStringTag (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.11 Symbol.unscopables

- -

The initial value of Symbol.unscopables is the well known symbol @@unscopables (Table - 1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.4.2.12 Symbol[ @@create ] ( )

- -

The @@create method of a Symbol object F performs the following steps:

- -
    -
  1. Throw a TypeError exception.
    2. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

19.4.3 Properties of the Symbol Prototype Object

- -

The Symbol prototype object is an ordinary object. It is not a Symbol instance and does not have a [[SymbolData]] internal slot.

- -

The value of the [[Prototype]] internal slot of the - Symbol prototype object is the standard built-in Object prototype object (19.1.3).

-
- -
-

19.4.3.1 Symbol.prototype.constructor

- -

The initial value of Symbol.prototype.constructor is the built-in Symbol constructor.

-
- -
-

19.4.3.2 Symbol.prototype.toString ( )

- -

The following steps are taken:

- -
    -
  1. Let s be the this value.
    2. -
  2. If Type(s) is Symbol, then let sym be - s.
    3. -
  3. Else, -
      -
    1. If s does not have a [[SymbolData]] internal - slot, then throw a TypeError exception.
      2. -
    2. Let sym be the value of s’s [[SymbolData]] internal slot.
      3. -
    -
    4. -
  4. Let desc be the value of sym’s [[Description]] attribute.
    5. -
  5. If desc is undefined, then let desc be the empty string.
    6. -
  6. Assert: Type(desc) is String.
    7. -
  7. Let result be the result of concatenating the strings "Symbol(", desc, and - ")".
    8. -
  8. Return result.
    9. -
-
- -
-

19.4.3.3 Symbol.prototype.valueOf ( )

- -

The following steps are taken:

- -
    -
  1. Let s be the this value.
    2. -
  2. If Type(s) is Symbol, then return s.
    3. -
  3. If s does not have a [[SymbolData]] internal - slot, then throw a TypeError exception.
    4. -
  4. Return the value of s’s [[SymbolData]] internal slot.
    5. -
-
- -
-

19.4.3.4 Symbol.prototype [ @@toPrimitive ] ( hint )

- -

This function is called by ECMAScript language operators to convert an object to a primitive value. The allowed values - for hint are "default", "number", and "string". Implicit conversion of - Symbol objects to primitive values is not allowed.

- -

When the @@toPrimitive method is called with argument hint, the following steps are taken:

- -
    -
  1. Throw a TypeError exception.
    2. -
- -

The value of the name property of this function is "[Symbol.toPrimitive]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

19.4.3.5 Symbol.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Symbol".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

19.4.4 Properties of Symbol Instances

- -

Symbol instances are ordinary objects that inherit properties from the Symbol prototype object. Symbol instances have a - [[SymbolData]] internal slot. The [[SymbolData]] internal slot is the Symbol value represented by this Symbol - object.

-
-
- -
-
-

19.5 Error - Objects

- -

Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base - objects for user-defined exception classes.

-
- -
-
-

19.5.1 - The Error Constructor

- -

The Error constructor is the %Error% intrinsic object and the initial value of the Error property of the - global object. When Error is called as a function rather than as a constructor, it creates and initializes a - new Error object. Thus the function call Error(…) is equivalent to the object creation - expression new Error(…) with the same arguments. However, if the this value - passed in the call is an Object with an uninitialized [[ErrorData]] internal slot, it initializes the this value using the - argument value rather than creating a new object. This permits Error to be used both as factory method and to - perform constructor instance initialization.

- -

The Error constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - Error behaviour should include a super call to the Error constructor to initialize - subclass instances.

-
- -
-

19.5.1.1 - Error ( message )

- -

When the Error function is called with argument message the following steps are taken:

- -
    -
  1. Let func be this Error function object.
    2. -
  2. Let O be the this value.
    3. -
  3. If Type(O) is not Object or Type(O) is Object and O does not have an - [[ErrorData]] internal slot or Type(O) is Object and O has an [[ErrorData]] internal slot and the value of [[ErrorData]] is not - undefined, then -
      -
    1. Let O be the result of calling OrdinaryCreateFromConstructor(func, - "%ErrorPrototype%",
      ( [[ErrorData]]) ).
      2. -
    2. ReturnIfAbrupt(O).
      3. -
    -
    4. -
  4. Assert: Type(O) - is Object.
    5. -
  5. Set the value of O’s [[ErrorData]] internal - slot to any value other than undefined.
    6. -
  6. If message is not undefined, then -
      -
    1. Let msg be ToString(message).
      2. -
    2. ReturnIfAbrupt(msg).
      3. -
    3. Let msgDesc be the PropertyDescriptor{[[Value]]: msg, [[Writable]]: true, [[Enumerable]]: - false, [[Configurable]]: true}.
      4. -
    4. Let status be the result of DefinePropertyOrThrow(O, - "message", msgDesc).
      5. -
    5. ReturnIfAbrupt(status).
      6. -
    -
    7. -
  7. Return O.
    8. -
-
- -
-

19.5.1.2 new Error ( ...argumentsList )

- -

When Error called as part of a new expression with argument list argumentsList it performs the - following steps:

- -
    -
  1. Let F be the Error function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If Error is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

19.5.2 Properties of the Error Constructor

- -

The value of the [[Prototype]] internal slot of the Error - constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Error constructor has the following - properties:

-
- -
-

19.5.2.1 - Error.prototype

- -

The initial value of Error.prototype is the Error prototype object (19.5.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.5.2.2 - Error[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%ErrorPrototype%", ( [[ErrorData]]) ).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE [[ErrorData]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the Error constructor. This flag value is never directly exposed to - ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

19.5.3 Properties of the Error Prototype Object

- -

The Error prototype object is an ordinary object. It is not an Error instance and does not have an [[ErrorData]] internal slot.

- -

The value of the [[Prototype]] internal slot of the Error - prototype object is the standard built-in Object prototype object (19.1.3).

-
- -
-

19.5.3.1 Error.prototype.constructor

- -

The initial value of Error.prototype.constructor is the built-in Error constructor.

-
- -
-

19.5.3.2 Error.prototype.message

- -

The initial value of Error.prototype.message is the empty String.

-
- -
-

19.5.3.3 Error.prototype.name

- -

The initial value of Error.prototype.name is "Error".

-
- -
-

19.5.3.4 Error.prototype.toString ( )

- -

The following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. Let name be the result of Get(O, "name").
    4. -
  4. ReturnIfAbrupt(name).
    5. -
  5. If name is undefined, then let name be "Error"; else let name be ToString(name).
    6. -
  6. Let msg be the result of Get(O, "message").
    7. -
  7. ReturnIfAbrupt(msg).
    8. -
  8. If msg is undefined, then let msg be the empty String; else let msg be ToString(msg).
    9. -
  9. If name is the empty String, return msg.
    10. -
  10. If msg is the empty String, return name.
    11. -
  11. Return the result of concatenating name, ":", a single space character, and msg.
    12. -
-
-
- -
-

19.5.4 Properties of Error Instances

- -

Error instances are ordinary objects that inherit properties from the Error prototype object and have an [[ErrorData]] internal slot whose initial value is undefined. The only specified uses of [[ErrorData]] is to flag whether or not an Error instance has - been initialized by the Error constructor and to identify them as Error objects within Object.prototype.toString.

-
- -
-
-

19.5.5 Native Error Types Used in This Standard

- -

A new instance of one of the NativeError objects below is thrown when a runtime error is detected. All of these - objects share the same structure, as described in 19.5.6.

-
- -
-

19.5.5.1 EvalError

- -

This exception is not currently used within this specification. This object remains for compatibility with previous - editions of this specification.

-
- -
-

19.5.5.2 RangeError

- -

Indicates a value that is not in the set or range of allowable values. See 15.4.2.2, 15.4.5.1, 15.7.4.2, 15.7.4.5, - 15.7.4.6, 15.7.4.7, and 15.9.5.43.

-
- -
-

19.5.5.3 ReferenceError

- -

Indicate that an invalid reference value has been detected. See 8.9.1, 8.9.2, 10.2.1, 10.2.1.1.4, 10.2.1.2.4, and 11.13.1.

-
- -
-

19.5.5.4 SyntaxError

- -

Indicates that a parsing error has occurred. See 11.1.5, 11.3.1, 11.3.2, 11.4.1, 11.4.4, 11.4.5, 11.13.1, 11.13.2, 12.2.1, 12.10.1, - 12.14.1, 13.1, 15.1.2.1, - 15.3.2.1, 15.10.2.2, 15.10.2.5, 15.10.2.9, 15.10.2.15, 15.10.2.19, 15.10.4.1, and 15.12.2.

-
- -
-

19.5.5.5 TypeError

- -

Indicates the actual type of an operand is different than the expected type. See 8.6.2, 8.9.2, 8.10.5, 8.12.5, 8.12.7, - 8.12.8, 8.12.9, 9.9, 9.10, 10.2.1, 10.2.1.1.3, 10.6, 11.2.2, 11.2.3, 11.4.1, 11.8.6, 11.8.7, 11.3.1, 13.2, 13.2.3, - 15, 15.2.3.2, 15.2.3.3, 15.2.3.4, 15.2.3.5, 15.2.3.6, 15.2.3.7, - 15.2.3.8, 15.2.3.9, 15.2.3.10, 15.2.3.11, 15.2.3.12, 15.2.3.13, 15.2.3.14, 15.2.4.3, - 15.3.3.2, 15.3.3.3, 15.3.3.4, 15.3.3.5, 15.3.3.5.2, 15.3.3.5.3, 15.3.4, 15.3.4.3, 15.3.4.4, 15.4.3.3, 15.4.3.11, - 15.4.3.16, 15.4.3.17, 15.4.3.18, 15.4.3.19, 15.4.3.20, 15.4.3.21, 15.4.3.22, 15.4.5.1, 15.5.4.2, 15.5.4.3, 15.6.4.2, - 15.6.4.3, 15.7.4, 15.7.4.2, 15.7.4.4, 15.9.5, 15.9.5.44, 15.10.4.1, 15.10.6, 15.11.4.4 and 15.12.3.

-
- -
-

19.5.5.6 URIError

- -

Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition. See - 15.1.3.

-
-
- -
-
-

19.5.6 NativeError Object Structure

- -

When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the NativeError - objects defined in 19.5.5. Each of these objects has the - structure described below, differing only in the name used as the constructor name instead of NativeError, in the - name property of the prototype object, and in the implementation-defined message property of the - prototype object.

- -

For each error object, references to NativeError in the definition should be replaced with the appropriate error - object name from 19.5.5.

-
- -
-
-

19.5.6.1 NativeError Constructors

- -

When a NativeError constructor is called as a function rather than as a constructor, it creates and - initializes a new object. A call of the object as a function is equivalent to calling it as a constructor with the same - arguments. However, if the this value passed in the call is an Object with an uninitialized [[ErrorData]] internal slot, it initializes the this value using the - argument value. This permits a NativeError to be used both as factory method and to perform constructor instance - initialization.

- -

The NativeError constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - NativeError behaviour should include a super call to the NativeError constructor to - initialize subclass instances.

-
- -
-

19.5.6.1.1 NativeError ( message )

- -

When a NativeError function is called with argument message the following steps are taken:

- -
    -
  1. Let func be this NativeError function object.
    2. -
  2. Let O be the this value.
    3. -
  3. If Type(O) is not Object or Type(O) is Object and O does not have an - [[ErrorData]] internal slot or Type(O) is Object and O has an [[ErrorData]] internal slot and the value of [[ErrorData]] is not - undefined, then -
      -
    1. Let O be the result of calling OrdinaryCreateFromConstructor(func, - "%NativeErrorPrototype%", ( [[ErrorData]]) ).
      2. -
    2. ReturnIfAbrupt(O).
      3. -
    -
    4. -
  4. Assert: Type(O) is Object.
    5. -
  5. Set the value of O’s [[ErrorData]] internal - slot to any value other than undefined.
    6. -
  6. If message is not undefined, then -
      -
    1. Let msg be ToString(message).
      2. -
    2. Let msgDesc be the PropertyDescriptor{[[Value]]: msg, [[Writable]]: true, [[Enumerable]]: - false, [[Configurable]]: true}.
      3. -
    3. Let status be the result of DefinePropertyOrThrow(O, - "message", msgDesc).
      4. -
    4. ReturnIfAbrupt(status).
      5. -
    -
    7. -
  7. Return O.
    8. -
- -

The actual value of the string passed in step 3.a is either "%EvalErrorPrototype%", - "%RangeErrorPrototype%", "%ReferenceErrorPrototype%", "%SyntaxErrorPrototype%", - "%TypeErrorPrototype%", or "%URIErrorPrototype%" corresponding to which NativeError - constructor is being defined.

-
- -
-

19.5.6.1.2 new NativeError ( ...argumentsList )

- -

When a NativeError constructor is called as part of a new expression with argument list argumentsList - it performs the following steps:

- -
    -
  1. Let F be this NativeError function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was - invoked by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If a NativeError constructor is implemented as an ECMAScript - function object, its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

19.5.6.2 Properties of the NativeError Constructors

- -

The value of the [[Prototype]] internal slot of a - NativeError constructor is the Error constructor object (19.5.1).

- -

Besides the length property (whose value is 1), each NativeError constructor has the - following properties:

-
- -
-

19.5.6.2.1 NativeError.prototype

- -

The initial value of NativeError.prototype is a NativeError prototype object (19.5.6.3). Each NativeError constructor has a - separate prototype object.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

19.5.6.2.2 NativeError [ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be OrdinaryCreateFromConstructor(F, - NativeErrorPrototype, ([[ErrorData]]) ).
    3. -
  3. Return obj.
    4. -
- -

The actual value passed as NativeErrorPrototype in step 2 is either - "%EvalErrorPrototype%", "%RangeErrorPrototype%", "%ReferenceErrorPrototype%", - "%SyntaxErrorPrototype%", "%TypeErrorPrototype%", or "%URIErrorPrototype%" - corresponding to which NativeError constructor is being defined.

- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE [[ErrorData]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the NativeError constructor. This flag value is never - directly exposed to ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

19.5.6.3 Properties of the NativeError Prototype Objects

- -

Each NativeError prototype object is an ordinary object. It is not an Error instance and does not have an - [[ErrorData]] internal slot.

- -

The value of the [[Prototype]] internal slot of each - NativeError prototype object is the standard built-in Error prototype object (19.5.3).

-
- -
-

19.5.6.3.1 NativeError.prototype.constructor

- -

The initial value of the constructor property of the prototype for a given NativeError - constructor is the NativeError constructor function itself (19.5.6.1).

-
- -
-

19.5.6.3.2 NativeError.prototype.message

- -

The initial value of the message property of the prototype for a given NativeError constructor is - the empty String.

-
- -
-

19.5.6.3.3 NativeError.prototype.name

- -

The initial value of the name property of the prototype for a given NativeError constructor is a - string consisting of the name of the constructor (the name used instead of NativeError).

-
-
- -
-

19.5.6.4 Properties of NativeError Instances

- -

NativeError instances are ordinary objects that inherit properties from their NativeError prototype - object and have an [[ErrorData]] internal slot whose initial - value is undefined. The only specified use of [[ErrorData]] is to flag whether or not an Error - or NativeError instance has been initialized by its constructor.

-
-
-
-
- -
-
-

20 Numbers and - Dates

-
- -
-
-

20.1 Number - Objects

-
- -
-
-

20.1.1 - The Number Constructor

- -

The Number constructor is the %Number% intrinsic object and the initial value of the Number property of - the global object. When Number is called as a function rather than as a constructor, it performs a type - conversion. However, if the this value passed in the call is an Object with an uninitialized [[NumberData]] internal slot, it initializes the this value using the - argument value. This permits Number to be used both to perform type conversion and to perform constructor - instance initialization.

- -

The Number constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - Number behaviour must include a super call to the Number constructor to initialize - the [[NumberData]] state of subclass instances.

-
- -
-

20.1.1.1 Number ( [ value ] )

- -

When Number is called with argument number, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If no arguments were passed to this function invocation, then let n be +0.
    3. -
  3. Else, let n be ToNumber(value).
    4. -
  4. ReturnIfAbrupt(n).
    5. -
  5. If Type(O) is Object and O has a [[NumberData]] internal slot and the value of [[NumberData]] is - undefined, then -
      -
    1. Set the value of O’s [[NumberData]] internal slot to n.
      2. -
    2. Return O.
      3. -
    -
    6. -
  6. Return n.
    7. -
-
- -
-

20.1.1.2 new Number ( ...argumentsList )

- -

When Number is called as part of a new expression with argument list argumentsListit performs the - following steps:

- -
    -
  1. Let F be the Number function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return Construct (F, argumentsList).
    4. -
- -

If Number is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

20.1.2 Properties of the Number Constructor

- -

The value of the [[Prototype]] internal slot of the - Number constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Number constructor has the following - properties:

-
- -
-

20.1.2.1 - Number.EPSILON

- -

The value of Number.EPSILON is the difference between 1 and the smallest value greater than 1 that is representable as - a Number value, which is approximately 2.2204460492503130808472633361816 x 10‍−‍16.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.2 - Number.isFinite ( number )

- -

When the Number.isFinite is called with one argument number, the following steps are taken:

- -
    -
  1. If Type(number) is not Number, return false.
    2. -
  2. If number is NaN, +∞, or −∞, return false.
    3. -
  3. Otherwise, return true.
    4. -
-
- -
-

20.1.2.3 Number.isInteger ( number )

- -

When the Number.isInteger is called with one argument number, the following steps are - taken:

- -
    -
  1. If Type(number) is not Number, return false.
    2. -
  2. If number is NaN, +∞, or −∞, return false.
    3. -
  3. Let integer be ToInteger(number).
    4. -
  4. If integer is not equal to number, return false.
    5. -
  5. Otherwise, return true.
    6. -
-
- -
-

20.1.2.4 - Number.isNaN ( number )

- -

When the Number.isNaN is called with one argument number, the following steps are taken:

- -
    -
  1. If Type(number) is not Number, return false.
    2. -
  2. If number is NaN, return true.
    3. -
  3. Otherwise, return false.
    4. -
- -
-

NOTE This function differs from the global isNaN function (18.2.3) is that it does not convert its argument to a Number before determining whether it - is NaN.

-
-
- -
-

20.1.2.5 Number.isSafeInteger ( number )

- -

When the Number.isSafeInteger is called with one argument number, the following steps are - taken:

- -
    -
  1. If Type(number) is not Number, return false.
    2. -
  2. If number is NaN, +∞, or −∞, return false.
    3. -
  3. Let integer be ToInteger(number).
    4. -
  4. If integer is not equal to number, return false.
    5. -
  5. If abs(integer) ≤ 253−1, then return - true.
    6. -
  6. Otherwise, return false.
    7. -
-
- -
-

20.1.2.6 Number.MAX_SAFE_INTEGER

- -

The value of Number.MAX_SAFE_INTEGER is 9007199254740991 (253−1).

- -


This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.7 Number.MAX_VALUE

- -

The value of Number.MAX_VALUE is the largest positive finite value of the Number type, which is - approximately 1.7976931348623157 × 10308.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.8 - Number.NaN

- -

The value of Number.NaN is NaN.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.9 Number.NEGATIVE_INFINITY

- -

The value of Number.NEGATIVE_INFINITY is −∞.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.10 Number.MIN_SAFE_INTEGER

- -

The value of Number.MIN_SAFE_INTEGER is −9007199254740991 (−(253−1)).

- -


This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.11 Number.MIN_VALUE

- -

The value of Number.MIN_VALUE is the smallest positive value of the Number type, which is approximately - 5 × 10−324.

- -

In the IEEE-764 double precision binary representation, the smallest possible value is a denormalized number. If an - implementation does not support denormalized values, the value of Number.MIN_VALUE must be the smallest - non-zero positive value that can actually be represented by the implementation.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.12 Number.parseFloat ( string )

- -

The value of the Number.parseFloat data property is the same built-in function object that is the value of - the parseFloat property of the global object defined in 18.2.4.

-
- -
-

20.1.2.13 Number.parseInt ( string, radix )

- -

The value of the Number.parseInt data property is the same built-in function object that is the value of - the parseInt property of the global object defined in 18.2.5.

-
- -
-

20.1.2.14 Number.POSITIVE_INFINITY

- -

The value of Number.POSITIVE_INFINITY is +∞.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.15 Number.prototype

- -

The initial value of Number.prototype is the Number prototype object (20.1.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.1.2.16 Number[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be OrdinaryCreateFromConstructor(F, - "%NumberPrototype%", ( [[NumberData]])).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE [[NumberData]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the Number constructor. This flag value is never directly exposed to - ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

20.1.3 Properties of the Number Prototype Object

- -

The Number prototype object is an ordinary object. It is not a Number instance and does not have a [[NumberData]] internal slot.

- -

The value of the [[Prototype]] internal slot of the - Number prototype object is the standard built-in Object prototype object (19.1.3).

- -

Unless explicitly stated otherwise, the methods of the Number prototype object defined below are not generic and the - this value passed to them must be either a Number value or an object that has a [[NumberData]] internal slot that has been initialized to a Number value.

- -

The abstract operation thisNumberValue(value) performs the - following steps:

- -
    -
  1. If Type(value) is Number, return value.
    2. -
  2. If Type(value) is Object and value has a - [[NumberData]] internal slot, then -
      -
    1. Let n be the value of value’s [[NumberData]] internal slot.
      2. -
    2. If n is not undefined, then return n.
      3. -
    -
    3. -
  3. Throw a TypeError exception.
    4. -
- -

The phrase “this Number value” within the specification of a method refers to the result returned by - calling the abstract operation thisNumberValue with the this - value of the method invocation passed as the argument.

-
- -
-

20.1.3.1 Number.prototype.constructor

- -

The initial value of Number.prototype.constructor is the built-in Number constructor.

-
- -
-

20.1.3.2 Number.prototype.toExponential ( fractionDigits )

- -

Return a String containing this Number value represented in decimal exponential notation with one digit before the - significand's decimal point and fractionDigits digits after the significand's decimal point. If - fractionDigits is undefined, include as many significand digits as necessary to uniquely specify the - Number (just like in ToString except that in this case the Number is always output in - exponential notation). Specifically, perform the following steps:

- -
    -
  1. Let x be thisNumberValue(this value).
    2. -
  2. ReturnIfAbrupt(x).
    3. -
  3. Let f be ToInteger(fractionDigits).
    4. -
  4. Assert: f is 0, when fractionDigits is undefined.
    5. -
  5. ReturnIfAbrupt(f).
    6. -
  6. If x is NaN, return the String "NaN".
    7. -
  7. Let s be the empty String.
    8. -
  8. If x < 0, then -
      -
    1. Let s be "-".
      2. -
    2. Let x = –x.
      3. -
    -
    9. -
  9. If x = +∞, then -
      -
    1. Return the concatenation of the Strings s and "Infinity".
      2. -
    -
    10. -
  10. If f < 0 or f > 20, throw a RangeError exception.
    11. -
  11. If x = 0, then -
      -
    1. Let m be the String consisting of f+1 occurrences of the code unit 0x0030.
      2. -
    2. Let e = 0.
      3. -
    -
    12. -
  12. Else x ≠ 0, -
      -
    1. If fractionDigits is not undefined, then -
        -
      1. Let e and n be integers such that 10f ≤ n < - 10f+1 and for which the exact mathematical value of n × - 10e–f – x is as close to zero as possible. If there are two such - sets of e and n, pick the e and n for which n × - 10e–f is larger.
        2. -
      -
      2. -
    2. Else fractionDigits is undefined, -
        -
      1. Let e, n, and f be integers such that f ≥ 0, 10f ≤ - n < 10f+1, the number value for n × 10e–f - is x, and f is as small as possible. Note that the decimal representation of n has - f+1 digits, n is not divisible by 10, and the least significant digit of n is not - necessarily uniquely determined by these criteria.
        2. -
      -
      3. -
    3. Let m be the String consisting of the digits of the decimal representation of n (in order, with no - leading zeroes).
      4. -
    -
    13. -
  13. If f ≠ 0, then -
      -
    1. Let a be the first element of m, and let b be the remaining f elements of - m.
      2. -
    2. Let m be the concatenation of the three Strings a, ".", and b.
      3. -
    -
    14. -
  14. If e = 0, then -
      -
    1. Let c = "+".
      2. -
    2. Let d = "0".
      3. -
    -
    15. -
  15. Else -
      -
    1. If e > 0, then let c = "+".
      2. -
    2. Else e ≤ 0, -
        -
      1. Let c = "-".
        2. -
      2. Let e = –e.
        3. -
      -
      3. -
    3. Let d be the String consisting of the digits of the decimal representation of e (in order, with no - leading zeroes).
      4. -
    -
    16. -
  16. Let m be the concatenation of the four Strings m, "e", c, and d.
    17. -
  17. Return the concatenation of the Strings s and m.
    18. -
- -

The length property of the toExponential method is 1.

- -

If the toExponential method is called with more than one argument, then the behaviour is undefined (see clause 17).

- -

An implementation is permitted to extend the behaviour of toExponential for values of - fractionDigits less than 0 or greater than 20. In this case toExponential would not necessarily - throw RangeError for such values.

- -
-

NOTE For implementations that provide more accurate conversions than required by the rules - above, it is recommended that the following alternative version of step 12.b.i be used as a guideline:

- -
    -
  1. Let e, n, and f be integers such that f ≥ 0, 10f ≤ n < - 10f+1, the number value for n × 10e–f is x, and f is - as small as possible. If there are multiple possibilities for n, choose the value of n for which - n × 10e–f is closest in value to x. If there are two such - possible values of n, choose the one that is even.
    2. -
-
-
- -
-

20.1.3.3 Number.prototype.toFixed ( fractionDigits )

- -
-

Note toFixed returns a String containing this Number value represented in decimal - fixed-point notation with fractionDigits digits after the decimal point. If fractionDigits is - undefined, 0 is assumed.

-
- -

The following steps are performed:

- -
    -
  1. Let x be thisNumberValue(this value).
    2. -
  2. ReturnIfAbrupt(x).
    3. -
  3. Let f be ToInteger(fractionDigits). (If fractionDigits is - undefined, this step produces the value 0).
    4. -
  4. ReturnIfAbrupt(f).
    5. -
  5. If f < 0 or f > 20, throw a RangeError exception.
    6. -
  6. If x is NaN, return the String "NaN".
    7. -
  7. Let s be the empty String.
    8. -
  8. If x < 0, then -
      -
    1. Let s be "-".
      2. -
    2. Let x = –x.
      3. -
    -
    9. -
  9. If x ≥ 1021, then -
      -
    1. Let m = ToString(x).
      2. -
    -
    10. -
  10. Else x < 1021, -
      -
    1. Let n be an integer for which the exact mathematical value of n ÷ 10f – - x is as close to zero as possible. If there are two such n, pick the larger n.
      2. -
    2. If n = 0, let m be the String "0". Otherwise, let m be the String consisting - of the digits of the decimal representation of n (in order, with no leading zeroes).
      3. -
    3. If f ≠ 0, then -
        -
      1. Let k be the number of elements in m.
        2. -
      2. If k ≤ f, then -
          -
        1. Let z be the String consisting of f+1–k occurrences of the code unit - 0x0030.
          2. -
        2. Let m be the concatenation of Strings z and m.
          3. -
        3. Let k = f + 1.
          4. -
        -
        3. -
      3. Let a be the first k–f elements of m, and let b be the remaining - f elements of m.
        4. -
      4. Let m be the concatenation of the three Strings a, ".", and b.
        5. -
      -
      4. -
    -
    11. -
  11. Return the concatenation of the Strings s and m.
    12. -
- -

The length property of the toFixed method is 1.

- -

If the toFixed method is called with more than one argument, then the behaviour is undefined (see clause 17).

- -

An implementation is permitted to extend the behaviour of toFixed for values of fractionDigits - less than 0 or greater than 20. In this case toFixed would not necessarily throw RangeError for such - values.

- -
-

NOTE The output of toFixed may be more precise than toString for - some values because toString only prints enough significant digits to distinguish the number from adjacent number - values. For example,

- -

(1000000000000000128).toString() returns "1000000000000000100",
while - (1000000000000000128).toFixed(0) returns "1000000000000000128".

-
-
- -
-

20.1.3.4 Number.prototype.toLocaleString( [ reserved1 [ , reserved2 ] ])

- -

An ECMAScript implementation that includes the ECMA-402 International API must implement the - Number.prototype.toLocaleString method as specified in the ECMA-402 specification. If an ECMAScript - implementation does not include the ECMA-402 API the following specification of the toLocaleString method is - used.

- -

Produces a String value that represents this Number value formatted according to the conventions of the host - environment’s current locale. This function is implementation-dependent, and it is permissible, but not encouraged, - for it to return the same thing as toString.

- -

The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that - do not include ECMA-402 support must not use those parameter position for anything else.

- -

The length property of the toLocaleString method is 0.

-
- -
-

20.1.3.5 Number.prototype.toPrecision ( precision )

- -

Return a String containing this Number value represented either in decimal exponential notation with one digit before - the significand's decimal point and precision–1 digits - after the significand's decimal point or in decimal fixed notation with precision significant digits. If - precision is undefined, call ToString (7.1.12) - instead. Specifically, perform the following steps:

- -
    -
  1. Let x be thisNumberValue(this value).
    2. -
  2. ReturnIfAbrupt(x).
    3. -
  3. If precision is undefined, return ToString(x).
    4. -
  4. Let p be ToInteger(precision).
    5. -
  5. ReturnIfAbrupt(p).
    6. -
  6. If x is NaN, return the String "NaN".
    7. -
  7. Let s be the empty String.
    8. -
  8. If x < 0, then -
      -
    1. Let s be "-".
      2. -
    2. Let x = –x.
      3. -
    -
    9. -
  9. If x = +∞, then -
      -
    1. Return the concatenation of the Strings s and "Infinity".
      2. -
    -
    10. -
  10. If p < 1 or p > 21, throw a RangeError exception.
    11. -
  11. If x = 0, then -
      -
    1. Let m be the String consisting of p occurrences of the code unit 0x0030 (the Unicode character - ‘0’).
      2. -
    2. Let e = 0.
      3. -
    -
    12. -
  12. Else x ≠ 0, -
      -
    1. Let e and n be integers such that 10p–1 ≤ n < - 10p and for which the exact mathematical value of n × - 10e–p+1 – x is as close to zero as possible. If there are two such - sets of e and n, pick the e and n for which n × - 10e–p+1 is larger.
      2. -
    2. Let m be the String consisting of the digits of the decimal representation of n (in order, with no - leading zeroes).
      3. -
    3. If e < –6 or e ≥ p, then -
        -
      1. Assert: e ≠ 0
        2. -
      2. Let a be the first element of m, and let b be the remaining p–1 elements - of m.
        3. -
      3. Let m be the concatenation of the three Strings a, ".", and b.
        4. -
      4. If e > 0, then -
          -
        1. Let c = "+".
          2. -
        -
        5. -
      5. Else e < 0, -
          -
        1. Let c = "-".
          2. -
        2. Let e = –e.
          3. -
        -
        6. -
      6. Let d be the String consisting of the digits of the decimal representation of e (in order, - with no leading zeroes).
        7. -
      7. Return the concatenation of the five Strings s, m, "e", c, and - d.
        8. -
      -
      4. -
    -
    13. -
  13. If e = p–1, then return the concatenation of the Strings s and m.
    14. -
  14. If e ≥ 0, then -
      -
    1. Let m be the concatenation of the first e+1 elements of m, the code unit 0x002E (Unicode - character ‘.’), and the remaining p– (e+1) elements of - m.
      2. -
    -
    15. -
  15. Else e < 0, -
      -
    1. Let m be the concatenation of the String "0.", –(e+1) occurrences of code unit - 0x0030 (the Unicode character ‘0’), and the String m.
      2. -
    -
    16. -
  16. Return the concatenation of the Strings s and m.
    17. -
- -

The length property of the toPrecision method is 1.

- -

If the toPrecision method is called with more than one argument, then the behaviour is undefined (see clause 17).

- -

An implementation is permitted to extend the behaviour of toPrecision for values of precision - less than 1 or greater than 21. In this case toPrecision would not necessarily throw RangeError for - such values.

-
- -
-

20.1.3.6 Number.prototype.toString ( [ radix ] )

- -
-

NOTE The optional radix should be an integer value in the inclusive range 2 to 36. If - radix not present or is undefined the Number 10 is used as the value of radix.

-
- -

The following steps are performed:

- -
    -
  1. Let x be thisNumberValue(this value).
    2. -
  2. ReturnIfAbrupt(x).
    3. -
  3. If radix is not present, then let radixNumber be 10.
    4. -
  4. Else if radix is undefined, then let radixNumber be 10.
    5. -
  5. Else let radixNumber be ToInteger(radix).
    6. -
  6. ReturnIfAbrupt(radixNumber).
    7. -
  7. If radixNumber < 2 or radixNumber > 36, then throw a RangeError exception.
    8. -
  8. If radixNumber = 10, then return ToString(x).
    9. -
  9. Return the String representation of this Number value using the radix specified by radixNumber. Letters - a-z are used for digits with values 10 through 35. The precise algorithm is - implementation-dependent, however the algorithm should be a generalisation of that specified in 7.1.12.1.
    10. -
- -

The toString function is not generic; it throws a TypeError exception if its this value is - not a Number or a Number object. Therefore, it cannot be transferred to other kinds of objects for use as a method.

-
- -
-

20.1.3.7 Number.prototype.valueOf ( )

-
    -
  1. Let x be thisNumberValue(this value).
    2. -
  2. Return x.
    3. -
-
-
- -
-

20.1.4 Properties of Number Instances

- -

Number instances are ordinary objects that inherit properties from the Number prototype object. Number instances also - have a [[NumberData]] internal slot. The [[NumberData]] internal slot is the Number value represented by this Number - object.

-
-
- -
-
-

20.2 The Math - Object

- -

The Math object is a single ordinary object.

- -

The value of the [[Prototype]] internal slot of the Math - object is the standard built-in Object prototype object (19.1.3).

- -

The Math is not a function object. It does not have a [[Construct]] internal method; it is not possible to use the Math - object as a constructor with the new operator. The Math object also does not have a [[Call]] internal method; - it is not possible to invoke the Math object as a function.

- -
-

NOTE In this specification, the phrase “the Number value for x” has a - technical meaning defined in 6.1.6.

-
-
- -
-
-

20.2.1 Value Properties of the Math Object

-
- -
-

20.2.1.1 - Math.E

- -

The Number value for e, the base of the natural logarithms, which is approximately - 2.7182818284590452354.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.2.1.2 - Math.LN10

- -

The Number value for the natural logarithm of 10, which is approximately 2.302585092994046.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.2.1.3 - Math.LOG10E

- -

The Number value for the base-10 logarithm of e, the base - of the natural logarithms; this value is approximately 0.4342944819032518.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

- -
-

NOTE The value of Math.LOG10E is approximately the reciprocal of the value of - Math.LN10.

-
-
- -
-

20.2.1.4 - Math.LN2

- -

The Number value for the natural logarithm of 2, which is approximately 0.6931471805599453.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.2.1.5 - Math.LOG2E

- -

The Number value for the base-2 logarithm of e, the base - of the natural logarithms; this value is approximately 1.4426950408889634.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

- -
-

NOTE The value of Math.LOG2E is approximately the reciprocal of the value of - Math.LN2.

-
-
- -
-

20.2.1.6 - Math.PI

- -

The Number value for π, the ratio of the circumference of a circle - to its diameter, which is approximately 3.1415926535897932.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.2.1.7 - Math.SQRT1_2

- -

The Number value for the square root of ½, which is - approximately 0.7071067811865476.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

- -
-

NOTE The value of Math.SQRT1_2 is approximately the reciprocal of the value of - Math.SQRT2.

-
-
- -
-

20.2.1.8 - Math.SQRT2

- -

The Number value for the square root of 2, which is approximately - 1.4142135623730951.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.2.1.9 Math [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Math".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-
-

20.2.2 Function Properties of the Math Object

- -

Each of the following Math object functions applies the ToNumber abstract - operation to each of its arguments (in left-to-right order if there is more than one). If ToNumber returns an abrupt completion, - that Completion Record is immediately returned. Otherwise, the - function performs a computation on the resulting Number value(s). The value returned by each function is a Number.

- -

In the function descriptions below, the symbols NaN, −0, +0, −∞ and +∞ refer to the Number - values described in 6.1.6.

- -
-

NOTE The behaviour of the functions acos, acosh, asin, - asinh, atan, atanh, atan2, cbrt, cos, - cosh, exp, hypot, log,log1p, log2, - log10, pow, sin, sinh, sqrt, tan, and - tanh is not precisely specified here except to require specific results for certain argument values that - represent boundary cases of interest. For other argument values, these functions are intended to compute approximations - to the results of familiar mathematical functions, but some latitude is allowed in the choice of approximation - algorithms. The general intent is that an implementer should be able to use the same mathematical library for ECMAScript - on a given hardware platform that is available to C programmers on that platform.

-
- -

Although the choice of algorithms is left to the implementation, it is recommended (but not specified by this standard) - that implementations use the approximation algorithms for IEEE 754 arithmetic contained in fdlibm, the freely - distributable mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm).

-
- -
-

20.2.2.1 - Math.abs ( x )

- -

Returns the absolute value of x; the result has the same magnitude as x but has positive - sign.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is −0, the result is +0.
    • -
  • If x is −∞, the result is +∞.
    • -
-
- -
-

20.2.2.2 - Math.acos ( x )

- -

Returns an implementation-dependent approximation to the arc cosine of x. The result is expressed in radians - and ranges from +0 to +π.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is greater than 1, the result is NaN.
    • -
  • If x is less than −1, the result is NaN.
    • -
  • If x is exactly 1, the result is +0.
    • -
-
- -
-

20.2.2.3 - Math.acosh( x )

- -

Returns an implementation-dependent approximation to the inverse hyperbolic cosine of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than 1, the result is NaN.
    • -
  • If x is 1, the result is +0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.4 - Math.asin ( x )

- -

Returns an implementation-dependent approximation to the arc sine of x. The result is expressed in radians - and ranges from −π/2 to +π/2.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is greater than 1, the result is NaN.
    • -
  • If x is less than –1, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
-
- -
-

20.2.2.5 - Math.asinh( x )

- -

Returns an implementation-dependent approximation to the inverse hyperbolic sine of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
-
- -
-

20.2.2.6 - Math.atan ( x )

- -

Returns an implementation-dependent approximation to the arc tangent of x. The result is expressed in - radians and ranges from −π/2 to +π/2.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is an implementation-dependent approximation to +π/2.
    • -
  • If x is −∞, the result is an implementation-dependent approximation to −π/2.
    • -
-
- -
-

20.2.2.7 - Math.atanh( x )

- -

Returns an implementation-dependent approximation to the inverse hyperbolic tangent of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than −1, the result is NaN.
    • -
  • If x is greater than 1, the result is NaN.
    • -
  • If x is −1, the result is −∞.
    • -
  • If x is +1, the result is +∞.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
-
- -
-

20.2.2.8 - Math.atan2 ( y, x )

- -

Returns an implementation-dependent approximation to the arc tangent of the quotient y/x of the arguments y and x, where the signs of y - and x are used to determine the quadrant of the result. Note that it is intentional and traditional for the - two-argument arc tangent function that the argument named y be first and the argument named x be - second. The result is expressed in radians and ranges from −π - to +π.

- -
    -
  • If either x or y is NaN, the result is NaN.
    • -
  • If y>0 and x is +0, the result is an implementation-dependent approximation to +π/2.
    • -
  • If y>0 and x is −0, the result is an implementation-dependent approximation to +π/2.
    • -
  • If y is +0 and x>0, the result is +0.
    • -
  • If y is +0 and x is +0, the result is +0.
    • -
  • If y is +0 and x is −0, the result is an implementation-dependent approximation to +π.
    • -
  • If y is +0 and x<0, the result is an implementation-dependent approximation to +π.
    • -
  • If y is −0 and x>0, the result is −0.
    • -
  • If y is −0 and x is +0, the result is −0.
    • -
  • If y is −0 and x is −0, the result is an implementation-dependent approximation to - −π.
    • -
  • If y is −0 and x<0, the result is an implementation-dependent approximation to - −π.
    • -
  • If y<0 and x is +0, the result is an implementation-dependent approximation to −π/2.
    • -
  • If y<0 and x is −0, the result is an implementation-dependent approximation to - −π/2.
    • -
  • If y>0 and y is finite and x is +∞, the result is +0.
    • -
  • If y>0 and y is finite and x is −∞, the result if an implementation-dependent - approximation to +π.
    • -
  • If y<0 and y is finite and x is +∞, the result is −0.
    • -
  • If y<0 and y is finite and x is −∞, the result is an implementation-dependent - approximation to −π.
    • -
  • If y is +∞ and x is finite, the result is an implementation-dependent approximation to - +π/2.
    • -
  • If y is −∞ and x is finite, the result is an implementation-dependent approximation to - −π/2.
    • -
  • If y is +∞ and x is +∞, the result is an implementation-dependent approximation to - +π/4.
    • -
  • If y is +∞ and x is −∞, the result is an implementation-dependent approximation to - +3π/4.
    • -
  • If y is −∞ and x is +∞, the result is an implementation-dependent approximation to - −π/4.
    • -
  • If y is −∞ and x is −∞, the result is an implementation-dependent - approximation to −3π/4.
    • -
-
- -
-

20.2.2.9 - Math.cbrt ( x )

- -

Returns an implementation-dependent approximation to the cube root of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
-
- -
-

20.2.2.10 - Math.ceil ( x )

- -

Returns the smallest (closest to −∞) Number value that is not less than x and is equal to - a mathematical integer. If x is already an integer, the result is x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
  • If x is less than 0 but greater than -1, the result is −0.
    • -
- -

The value of Math.ceil(x) is the same as the value of -Math.floor(-x).

-
- -
-

20.2.2.11 - Math.clz32 ( x )

- -

When Math.clz32 is called with one argument x, the following steps are taken:

- -
    -
  1. Let n be ToUint32(x).
    2. -
  2. ReturnIfAbrupt(n).
    3. -
  3. Let p be the number of leading zero bits in the 32-bit binary representation of n.
    4. -
  4. Return p.
    5. -
- -

NOTE If n is 0, p will be 32. If the most significant bit of the 32-bit binary encoding of - n is 1, p will be 0.

-
- -
-

20.2.2.12 - Math.cos ( x )

- -

Returns an implementation-dependent approximation to the cosine of x. The argument is expressed in - radians.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is 1.
    • -
  • If x is −0, the result is 1.
    • -
  • If x is +∞, the result is NaN.
    • -
  • If x is −∞, the result is NaN.
    • -
-
- -
-

20.2.2.13 - Math.cosh ( x )

- -

Returns an implementation-dependent approximation to the hyperbolic cosine of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is 1.
    • -
  • If x is −0, the result is 1.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is +∞.
    • -
- -
-

NOTE The value of cosh(x) is the same as (exp(x) + exp(-x))/2.

-
-
- -
-

20.2.2.14 - Math.exp ( x )

- -

Returns an implementation-dependent approximation to the exponential function of x (e raised to - the power of x, where e is the base of the natural logarithms).

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is 1.
    • -
  • If x is −0, the result is 1.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is +0.
    • -
-
- -
-

20.2.2.15 - Math.expm1 ( x )

- -

Returns an implementation-dependent approximation to subtracting 1 from the exponential function of x (e - raised to the power of x, where e is the base of the natural logarithms). The result is computed in a way - that is accurate even when the value of x is close 0.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −1.
    • -
-
- -
-

20.2.2.16 - Math.floor ( x )

- -

Returns the greatest (closest to +∞) Number value that is not greater than x and is equal to a - mathematical integer. If x is already an integer, the result is x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
  • If x is greater than 0 but less than 1, the result is +0.
    • -
- -
-

NOTE The value of Math.floor(x) is the - same as the value of -Math.ceil(-x).

-
-
- -
-

20.2.2.17 - Math.fround ( x )

- -

When Math.fround is called with argument x the following steps are taken:

- -
    -
  1. If x is NaN, return NaN.
    2. -
  2. If x is one of +0, −0, +∞, −∞, then return x.
    3. -
  3. Let x32 be the result of converting x to a value in IEEE-754-2008 binary32 format using - roundTiesToEven.
    4. -
  4. Let x64 be the result of converting x32 to a value in IEEE-754-2008 binary64 format.
    5. -
  5. Return the ECMAScript Number value corresponding to x64.
    6. -
-
- -
-

20.2.2.18 - Math.hypot ( value1 , value2 , …values )

- -

Math.hypot returns an implementation-dependent approximation of the square root of the sum of squares of - its arguments.

- -
    -
  • If no arguments are passed, the result is +0.
    • -
  • If any argument is +∞, the result is +∞.
    • -
  • If any argument is −∞, the result is +∞.
    • -
  • If no argument is +∞ or −∞, and any argument is NaN, the result is NaN.
    • -
  • If all arguments are either +0 or −0, the result is +0.
    • -
- -

The length property of the hypot function is 2.

- -
-

NOTE Implementations should take care to avoid the loss of precision from overflows and - underflows that are prone to occur in naive implementations when this function is called with more than two - arguments.

-
-
- -
-

20.2.2.19 - Math.imul ( x, y )

- -

When the Math.imul is called with arguments x and y the following steps are - taken:

- -
    -
  1. Let a be ToUint32(x).
    2. -
  2. ReturnIfAbrupt(a).
    3. -
  3. Let b be ToUint32(y).
    4. -
  4. ReturnIfAbrupt(b).
    5. -
  5. Let product be (a × b) modulo - 232.
    6. -
  6. If product ≥ 231, return product − 232, otherwise return - product.
    7. -
-
- -
-

20.2.2.20 - Math.log ( x )

- -

Returns an implementation-dependent approximation to the natural logarithm of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than 0, the result is NaN.
    • -
  • If x is +0 or −0, the result is −∞.
    • -
  • If x is 1, the result is +0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.21 - Math.log1p ( x )

- -

Returns an implementation-dependent approximation to the natural logarithm of 1 + x. The result is computed in - a way that is accurate even when the value of x is close to zero.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than -1, the result is NaN.
    • -
  • If x is -1, the result is -∞.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.22 - Math.log10 ( x )

- -

Returns an implementation-dependent approximation to the base 10 logarithm of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than 0, the result is NaN.
    • -
  • If x is +0, the result is −∞.
    • -
  • If x is −0, the result is −∞.
    • -
  • If x is 1, the result is +0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.23 - Math.log2 ( x )

- -

Returns an implementation-dependent approximation to the base 2 logarithm of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than 0, the result is NaN.
    • -
  • If x is +0, the result is −∞.
    • -
  • If x is −0, the result is −∞.
    • -
  • If x is 1, the result is +0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.24 - Math.max ( value1, value2 , …values )

- -

Given zero or more arguments, calls ToNumber on each of the arguments and returns the - largest of the resulting values.

- -
    -
  • -

    If no arguments are given, the result is −∞.

    -
    • - -
  • -

    If any value is NaN, the result is NaN.

    -
    • - -
  • -

    The comparison of values to determine the largest value is done using the Abstract Relational Comparison algorithm - (7.2.8) except that +0 is considered to be larger than −0.

    -
    • -
- -

The length property of the max method is 2.

-
- -
-

20.2.2.25 - Math.min ( value1, value2 , …values )

- -

Given zero or more arguments, calls ToNumber on each of the arguments and returns the - smallest of the resulting values.

- -
    -
  • -

    If no arguments are given, the result is +∞.

    -
    • - -
  • -

    If any value is NaN, the result is NaN.

    -
    • - -
  • -

    The comparison of values to determine the smallest value is done using the Abstract Relational Comparison algorithm - (7.2.8) except that +0 is considered to be larger than −0.

    -
    • -
- -

The length property of the min method is 2.

-
- -
-

20.2.2.26 - Math.pow ( x, y )

- -

Returns an implementation-dependent approximation to the result of raising x to the power y.

- -
    -
  • If y is NaN, the result is NaN.
    • -
  • If y is +0, the result is 1, even if x is NaN.
    • -
  • If y is −0, the result is 1, even if x is NaN.
    • -
  • If x is NaN and y is nonzero, the result is NaN.
    • -
  • If abs(x)>1 and y is +∞, the result is - +∞.
    • -
  • If abs(x)>1 and y is −∞, the result is - +0.
    • -
  • If abs(x) is 1 and y is +∞, the result is NaN.
    • -
  • If abs(x) is 1 and y is −∞, the result is - NaN.
    • -
  • If abs(x)<1 and y is +∞, the result is +0.
    • -
  • If abs(x)<1 and y is −∞, the result is - +∞.
    • -
  • If x is +∞ and y>0, the result is +∞.
    • -
  • If x is +∞ and y<0, the result is +0.
    • -
  • If x is −∞ and y>0 and y is an odd integer, the result is −∞.
    • -
  • If x is −∞ and y>0 and y is not an odd integer, the result is +∞.
    • -
  • If x is −∞ and y<0 and y is an odd integer, the result is −0.
    • -
  • If x is −∞ and y<0 and y is not an odd integer, the result is +0.
    • -
  • If x is +0 and y>0, the result is +0.
    • -
  • If x is +0 and y<0, the result is +∞.
    • -
  • If x is −0 and y>0 and y is an odd integer, the result is −0.
    • -
  • If x is −0 and y>0 and y is not an odd integer, the result is +0.
    • -
  • If x is −0 and y<0 and y is an odd integer, the result is −∞.
    • -
  • If x is −0 and y<0 and y is not an odd integer, the result is +∞.
    • -
  • If x<0 and x is finite and y is finite and y is not an integer, the result is - NaN.
    • -
-
- -
-

20.2.2.27 - Math.random ( )

- -

Returns a Number value with positive sign, greater than or equal to 0 but less than 1, chosen randomly or pseudo - randomly with approximately uniform distribution over that range, using an implementation-dependent algorithm or strategy. - This function takes no arguments.

- -

Each Math.random function created for distinct code Realms must produce a distinct sequence of values from - successive calls.

-
- -
-

20.2.2.28 - Math.round ( x )

- -

Returns the Number value that is closest to x and is equal to a mathematical integer. If two integer Number - values are equally close to x, then the result is the Number value that is closer to +∞. If x is already an integer, the result is x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
  • If x is greater than 0 but less than 0.5, the result is +0.
    • -
  • If x is less than 0 but greater than or equal to -0.5, the result is −0.
    • -
- -
-

NOTE 1 Math.round(3.5) returns 4, but Math.round(–3.5) - returns –3.

-
- -
-

NOTE 2 The value of Math.round(x) is not always the same as the value of - Math.floor(x+0.5). When x is −0 or is less than 0 but - greater than or equal to -0.5, Math.round(x) returns −0, but Math.floor(x+0.5) returns +0. Math.round(x) may also differ from the - value of Math.floor(x+0.5)because of - internal rounding when computing x+0.5.

-
-
- -
-

20.2.2.29 - Math.sign(x)

- -

Returns the sign of the x, indicating whether x is positive, negative or zero.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is negative and not −0, the result is −1.
    • -
  • If x is positive and not +0, the result is +1.
    • -
-
- -
-

20.2.2.30 - Math.sin ( x )

- -

Returns an implementation-dependent approximation to the sine of x. The argument is expressed in - radians.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞ or −∞, the result is NaN.
    • -
-
- -
-

20.2.2.31 - Math.sinh( x )

- -

Returns an implementation-dependent approximation to the hyperbolic sine of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
- -
-

NOTE The value of sinh(x) is the same as (exp(x) - exp(-x))/2.

-
-
- -
-

20.2.2.32 - Math.sqrt ( x )

- -

Returns an implementation-dependent approximation to the square root of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is less than 0, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +∞.
    • -
-
- -
-

20.2.2.33 - Math.tan ( x )

- -

Returns an implementation-dependent approximation to the tangent of x. The argument is expressed in - radians.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞ or −∞, the result is NaN.
    • -
-
- -
-

20.2.2.34 - Math.tanh ( x )

- -

Returns an implementation-dependent approximation to the hyperbolic tangent of x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +∞, the result is +1.
    • -
  • If x is −∞, the result is -1.
    • -
- -
-

NOTE The value of tanh(x) is the same as (exp(x) - exp(-x))/(exp(x) + exp(-x)).

-
-
- -
-

20.2.2.35 - Math.trunc ( x )

- -

Returns the integral part of the number x, removing any fractional digits. If x is already an - integer, the result is x.

- -
    -
  • If x is NaN, the result is NaN.
    • -
  • If x is −0, the result is −0.
    • -
  • If x is +0, the result is +0.
    • -
  • If x is +∞, the result is +∞.
    • -
  • If x is −∞, the result is −∞.
    • -
  • If x is greater than 0 but less than 1, the result is +0.
    • -
  • If x is less than 0 but greater than −1, the result is - −0.
    • -
-
-
-
- -
-
-

20.3 Date - Objects

-
- -
-
-

20.3.1 Overview of Date Objects and Definitions of Abstract Operations

- -

The following functions are abstract operations that operate on time values (defined in 20.3.1.1). Note that, in every case, if any argument to one of these functions - is NaN, the result will be NaN.

-
- -
-

20.3.1.1 Time Values and Time Range

- -

A Date object contains a Number indicating a particular instant in time to within a millisecond. Such a Number is - called a time value. A time value may also be NaN, indicating that the Date object does not represent a - specific instant of time.

- -

Time is measured in ECMAScript in milliseconds since 01 January, 1970 UTC. In time values leap seconds are ignored. It - is assumed that there are exactly 86,400,000 milliseconds per day. ECMAScript Number values can represent all integers - from –9,007,199,254,740,992 to 9,007,199,254,740,992; this range suffices to measure times to millisecond precision - for any instant that is within approximately 285,616 years, either forward or backward, from 01 January, 1970 UTC.

- -

The actual range of times supported by ECMAScript Date objects is slightly smaller: exactly –100,000,000 days to - 100,000,000 days measured relative to midnight at the beginning of 01 January, 1970 UTC. This gives a range of - 8,640,000,000,000,000 milliseconds to either side of 01 January, 1970 UTC.

- -

The exact moment of midnight at the beginning of 01 January, 1970 UTC is represented by the value +0.

-
- -
-

20.3.1.2 Day Number and Time within Day

- -

A given time value t belongs to day number

- -
Day(t) = floor(t / msPerDay)
- -

where the number of milliseconds per day is

- -
msPerDay = 86400000
- -

The remainder is called the time within the day:

- -
TimeWithinDay(t) = t modulo msPerDay
-
- -
-

20.3.1.3 - Year Number

- -

ECMAScript uses an extrapolated Gregorian system to map a day number to a year number and to determine the month and - date within that year. In this system, leap years are precisely those which are (divisible by 4) and ((not divisible by 100) or (divisible by - 400)). The number of days in year number y is therefore - defined by

- -
DaysInYear(y) = 365 if (y modulo 4) ≠ 0
= 366 if (y modulo 4) = 0 and (y modulo 100) ≠ 0
= 365 if (y modulo 100) = 0 and (y modulo 400) ≠ 0
= 366 if (y modulo 400) = 0
- -

All non-leap years have 365 days with the usual number of days per - month and leap years have an extra day in February. The day number of the first day of year y is given by:

- -
DayFromYear(y) = 365 × (y−1970) + floor((y−1969)/4) − floor((y−1901)/100) + floor((y−1601)/400)
- -

The time value of the start of a year is:

- -
TimeFromYear(y) = msPerDay × DayFromYear(y)
- -

A time value determines a year by:

- -
YearFromTime(t) = the largest integer y (closest to positive infinity) such that TimeFromYear(y) ≤ t
- -

The leap-year function is 1 for a time within a leap year and otherwise is zero:

- -
InLeapYear(t) = 0 if DaysInYear(YearFromTime(t)) = 365
= 1 if DaysInYear(YearFromTime(t)) = 366
-
- -
-

20.3.1.4 - Month Number

- -

Months are identified by an integer in the range 0 to 11, inclusive. The mapping MonthFromTime(t) from a time value t to a month number is defined by:

- -
MonthFromTime(t) = 0 if 0 ≤ DayWithinYear(t) < 31
= 1 if 31 ≤ DayWithinYear (t) < 59+InLeapYear(t)
= 2 if 59+InLeapYear(t) ≤ DayWithinYear (t) < 90+InLeapYear(t)
= 3 if 90+InLeapYear(t) ≤ DayWithinYear (t) < 120+InLeapYear(t)
= 4 if 120+InLeapYear(t) ≤ DayWithinYear (t) < 151+InLeapYear(t)
= 5 if 151+InLeapYear(t) ≤ DayWithinYear (t) < 181+InLeapYear(t)
= 6 if 181+InLeapYear(t) ≤ DayWithinYear (t) < 212+InLeapYear(t)
= 7 if 212+InLeapYear(t) ≤ DayWithinYear (t) < 243+InLeapYear(t)
= 8 if 243+InLeapYear(t) ≤ DayWithinYear (t) < 273+InLeapYear(t)
= 9 if 273+InLeapYear(t) ≤ DayWithinYear (t) < 304+InLeapYear(t)
= 10 if 304+InLeapYear(t) ≤ DayWithinYear (t) < 334+InLeapYear(t)
= 11 if 334+InLeapYear(t) ≤ DayWithinYear (t) < 365+InLeapYear(t)
- -

where

- -
DayWithinYear(t) = Day(t)−DayFromYear(YearFromTime(t))
- -

A month value of 0 specifies January; 1 specifies February; 2 specifies March; 3 specifies April; 4 specifies May; 5 specifies June; 6 specifies July; 7 - specifies August; 8 specifies September; 9 specifies October; 10 specifies November; and 11 specifies December. Note that MonthFromTime(0) = 0, corresponding to Thursday, 01 January, 1970.

-
- -
-

20.3.1.5 - Date Number

- -

A date number is identified by an integer in the range 1 through - 31, inclusive. The mapping DateFromTime(t) from a time value t to a month number is defined by:

- -
DateFromTime(t) = DayWithinYear(t)+1 if MonthFromTime(t)=0
= DayWithinYear(t)−30 if MonthFromTime(t)=1
= DayWithinYear(t)−58−InLeapYear(t) if MonthFromTime(t)=2
= DayWithinYear(t)−89−InLeapYear(t) if MonthFromTime(t)=3
= DayWithinYear(t)−119−InLeapYear(t) if MonthFromTime(t)=4
= DayWithinYear(t)−150−InLeapYear(t) if MonthFromTime(t)=5
= DayWithinYear(t)−180−InLeapYear(t) if MonthFromTime(t)=6
= DayWithinYear(t)−211−InLeapYear(t) if MonthFromTime(t)=7
= DayWithinYear(t)−242−InLeapYear(t) if MonthFromTime(t)=8
= DayWithinYear(t)−272−InLeapYear(t) if MonthFromTime(t)=9
= DayWithinYear(t)−303−InLeapYear(t) if MonthFromTime(t)=10
= DayWithinYear(t)−333−InLeapYear(t) if MonthFromTime(t)=11
-
- -
-

20.3.1.6 Week - Day

- -

The weekday for a particular time value t is defined as

- -
WeekDay(t) = (Day(t) + 4) modulo 7
- -

A weekday value of 0 specifies Sunday; 1 specifies Monday; 2 specifies Tuesday; 3 specifies Wednesday; 4 specifies Thursday; 5 specifies Friday; and 6 specifies Saturday. Note that WeekDay(0) = 4, corresponding to Thursday, 01 January, 1970.

-
- -
-

20.3.1.7 Local Time Zone Adjustment

- -

An implementation of ECMAScript is expected to determine the local time zone adjustment. The local time zone adjustment - is a value LocalTZA measured in milliseconds which when added to UTC represents the local standard time. Daylight - saving time is not reflected by LocalTZA.

- -
-

NOTE It is recommended that implementations use the time zone information of the IANA Time - Zone Database.

-
-
- -
-

20.3.1.8 Daylight Saving Time Adjustment

- -

An implementation dependent algorithm using best available information on time zones to determine the local daylight - saving time adjustment DaylightSavingTA(t), measured in milliseconds. An implementation of ECMAScript is expected - to make its best effort to determine the local daylight saving time adjustment.

-
- -
-

20.3.1.9 - Local Time

- -

Conversion from UTC to local time is defined by

- -
LocalTime(t) = t + LocalTZA + DaylightSavingTA(t)
- -

Conversion from local time to UTC is defined by

- -
UTC(t) = t – LocalTZA – DaylightSavingTA(t – LocalTZA)
- -
-

NOTE UTC(LocalTime(t)) is not necessarily always equal to t.

-
-
- -
-

20.3.1.10 Hours, Minutes, Second, and Milliseconds

- -

The following functions are useful in decomposing time values:

- -
HourFromTime(t) = floor(t / msPerHour) modulo HoursPerDay
-
MinFromTime(t) = floor(t / msPerMinute) modulo MinutesPerHour
-
SecFromTime(t) = floor(t / msPerSecond) modulo SecondsPerMinute
-
msFromTime(t) = t modulo msPerSecond
- -

where

- -
HoursPerDay = 24
-
MinutesPerHour = 60
-
SecondsPerMinute = 60
-
msPerSecond = 1000
-
msPerMinute = 60000 = msPerSecond × SecondsPerMinute
-
msPerHour = 3600000 = msPerMinute × MinutesPerHour
-
- -
-

20.3.1.11 - MakeTime (hour, min, sec, ms)

- -

The operator MakeTime calculates a number of milliseconds from its four arguments, which must be ECMAScript Number - values. This operator functions as follows:

- -
    -
  1. If hour is not finite or min is not finite or sec is not finite or ms is not finite, - return NaN.
    2. -
  2. Let h be ToInteger(hour).
    3. -
  3. Let m be ToInteger(min).
    4. -
  4. Let s be ToInteger(sec).
    5. -
  5. Let milli be ToInteger(ms).
    6. -
  6. Let t be h * msPerHour - + m * msPerMinute - + s * msPerSecond - + milli, performing the arithmetic according to IEEE 754 rules (that is, as if using the - ECMAScript operators * and +).
    7. -
  7. Return t.
    8. -
-
- -
-

20.3.1.12 - MakeDay (year, month, date)

- -

The operator MakeDay calculates a number of days from its three arguments, which must be ECMAScript Number values. This - operator functions as follows:

- -
    -
  1. If year is not finite or month is not finite or date is not finite, return NaN.
    2. -
  2. Let y be ToInteger(year).
    3. -
  3. Let m be ToInteger(month).
    4. -
  4. Let dt be ToInteger(date).
    5. -
  5. Let ym be y + floor(m /12).
    6. -
  6. Let mn be m modulo 12.
    7. -
  7. Find a value t such that YearFromTime(t) is ym and MonthFromTime(t) is mn and DateFromTime(t) is 1; but if this is not possible (because some argument is out - of range), return NaN.
    8. -
  8. Return Day(t) + dt − 1.
    9. -
-
- -
-

20.3.1.13 - MakeDate (day, time)

- -

The operator MakeDate calculates a number of milliseconds from its two arguments, which must be ECMAScript Number - values. This operator functions as follows:

- -
    -
  1. If day is not finite or time is not finite, return NaN.
    2. -
  2. Return day × msPerDay + time.
    3. -
-
- -
-

20.3.1.14 - TimeClip (time)

- -

The operator TimeClip calculates a number of milliseconds from its argument, which must be an ECMAScript Number value. - This operator functions as follows:

- -
    -
  1. If time is not finite, return NaN.
    2. -
  2. If abs(time) > 8.64 × 1015, return NaN.
    3. -
  3. Return ToInteger(time) + (+0). (Adding a positive zero converts - −0 to +0.)
    4. -
- -
-

NOTE The point of step 3 is that an implementation is permitted a choice of internal - representations of time values, for example as a 64-bit signed integer or as a 64-bit floating-point value. Depending on - the implementation, this internal representation may or may not distinguish −0 and +0.

-
-
- -
-
-

20.3.1.15 Date Time String Format

- -

ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO 8601 Extended - Format. The format is as follows: YYYY-MM-DDTHH:mm:ss.sssZ

- -

Where the fields are as follows:

- -

YYYY is the decimal digits of the year 0000 to 9999 in the - Gregorian calendar.

- -

- “-” (hyphen) appears literally twice in the string.

- -

MM is the month of the year from 01 (January) to 12 - (December).

- -

DD is the day of the month from 01 to 31.

- -

T “T” appears literally in the string, to indicate the beginning of the time element.

- -

HH is the number of complete hours that have passed since - midnight as two decimal digits from 00 to 24.

- -

: “:” (colon) appears literally twice in the string.

- -

mm is the number of complete minutes since the start of the - hour as two decimal digits from 00 to 59.

- -

ss is the number of complete seconds since the start of the - minute as two decimal digits from 00 to 59.

- -

. “.” (dot) appears literally in the string.

- -

sss is the number of complete milliseconds since the start of - the second as three decimal digits.

- -

Z is the time zone offset specified as - “Z” (for UTC) or either - “+” or “-” followed by a time expression HH:mm

- -

This format includes date-only forms:

- - 
YYYY
YYYY-MM
YYYY-MM-DD
- -

It also includes “date-time” forms that consist of one of the above date-only forms immediately followed - by one of the following time forms with an optional time zone offset appended:

- - 
THH:mm
THH:mm:ss
THH:mm:ss.sss
- -

All numbers must be base 10. If the MM or - DD fields are absent “01” is used as the value. If the HH, - mm, or ss fields are absent “00” is used as the value and the value - of an absent sss field is “000”. If the time zone offset is absent, the date-time - is interpreted as a local time.

- -

Illegal values (out-of-bounds as well as syntax errors) in a format string means that the format string is not a - valid instance of this format.

- -
-

NOTE 1 As every day both starts and ends with midnight, the two notations - 00:00 and 24:00 are available to distinguish the two midnights that can be associated with - one date. This means that the following two notations refer to exactly the same point in time: - 1995-02-04T24:00 and 1995-02-05T00:00

-
- -
-

NOTE 2 There exists no international standard that specifies abbreviations for civil time - zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this - reason, ISO 8601 and this format specifies numeric representations of date and time.

-
-
- -
-

20.3.1.15.1 Extended years

- -

ECMAScript requires the ability to specify 6 digit years (extended - years); approximately 285,426 years, either forward or backward, from - 01 January, 1970 UTC. To represent years before 0 or after 9999, ISO 8601 permits the expansion of the year representation, but only by - prior agreement between the sender and the receiver. In the simplified ECMAScript format such an expanded year - representation shall have 2 extra year digits and is always prefixed - with a + or – sign. The year 0 is considered positive and hence - prefixed with a + sign.

- -
-

NOTE Examples of extended years:

- -

-283457-03-21T15:00:59.008Z 283458 B.C.
-000001-01-01T00:00:00Z 2 B.C.
+000000-01-01T00:00:00Z 1 B.C.
+000001-01-01T00:00:00Z 1 A.D.
+001970-01-01T00:00:00Z 1970 A.D.
+002009-12-15T00:00:00Z 2009 A.D.
+287396-10-12T08:59:00.992Z 287396 A.D.

-
-
-
-
- -
-
-

20.3.2 - The Date Constructor

- -

The Date constructor is the %Date% intrinsic object and the initial value of the Date property of the - global object. When Date is called as a function rather than as a constructor, it returns a String - representing the current time (UTC). However, if the this value passed in the call is an Object with an - uninitialized [[DateValue]] internal slot, Date - initializes the this object using the argument value. This permits Date to be used both as a function - for creating data strings and to perform constructor instance initialization.

- -

The Date constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - Date behaviour must include a super call to the Date constructor to initialize the - [[DateValue]] state of subclass instances.

-
- -
-

20.3.2.1 Date ( year, month [, date [ , hours [ , minutes [ , seconds [ , ms ] - ] ] ] ] )

- -

This description applies only if the Date constructor is called with at least two arguments.

- -

When the Date function is called the following steps are taken:

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs ≥ 2.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has a [[DateValue]] internal slot and the value of [[DateValue]] is - undefined, then -
      -
    1. Let y be ToNumber(year).
      2. -
    2. ReturnIfAbrupt(year).
      3. -
    3. Let m be ToNumber(month).
      4. -
    4. ReturnIfAbrupt(month).
      5. -
    5. If date is supplied then let dt be ToNumber(date); else let - dt be 1.
      6. -
    6. ReturnIfAbrupt(dt).
      7. -
    7. If hours is supplied then let h be ToNumber(hours); else let - h be 0.
      8. -
    8. ReturnIfAbrupt(h).
      9. -
    9. If minutes is supplied then let min be ToNumber(minutes); else - let min be 0.
      10. -
    10. ReturnIfAbrupt(min).
      11. -
    11. If seconds is supplied then let s be ToNumber(seconds); else - let s be 0.
      12. -
    12. ReturnIfAbrupt(s).
      13. -
    13. If ms is supplied then let milli be ToNumber(ms); else let - milli be 0.
      14. -
    14. ReturnIfAbrupt(milli).
      15. -
    15. If y is not NaN and 0 ≤ ToInteger(y) ≤ 99, then let yr be 1900+ToInteger(y); otherwise, let yr be y.
      16. -
    16. Let finalDate be MakeDate(MakeDay(yr, - m, dt), MakeTime(h, min, s, milli)).
      17. -
    17. Set the [[DateValue]] internal slot of O to - TimeClip(UTC(finalDate)).
      18. -
    18. Return O.
      19. -
    -
    5. -
  5. Else, -
      -
    1. Let now be the Number that is the time value (UTC) - identifying the current time.
      2. -
    2. Return ToDateString (now).
      3. -
    -
    6. -
-
- -
-

20.3.2.2 Date - ( value )

- -

This description applies only if the Date constructor is called with exactly one argument.

- -

When the Date function is called the following steps are taken:

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs = 1.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has a [[DateValue]] internal slot and the value of [[DateValue]] is - undefined, then -
      -
    1. If Type(value) is Object and value has a - [[DateValue]] internal slot, then -
        -
      1. Let tv be thisTimeValue(value).
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let v be ToPrimitive(value).
        2. -
      2. If Type(v) is String, then -
          -
        1. Let tv be the result of parsing v as a date, in exactly the same manner as for the - parse method (20.3.3.2). If the parse resulted in an abrupt completion, tv is the Completion Record.
          2. -
        -
        3. -
      3. Else, -
          -
        1. Let tv be ToNumber(v).
          2. -
        -
        4. -
      -
      3. -
    3. ReturnIfAbrupt(tv).
      4. -
    4. Set the [[DateValue]] internal slot of O to - TimeClip(tv).
      5. -
    5. Return O.
      6. -
    -
    5. -
  5. Else, -
      -
    1. Let now be the Number that is the time value (UTC) - identifying the current time.
      2. -
    2. Return ToDateString (now).
      3. -
    -
    6. -
-
- -
-

20.3.2.3 Date ( )

- -

This description applies only if the Date constructor is called with no arguments.

- -

When the Date function is called the following steps are taken:

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs = 0.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has a [[DateValue]] internal slot and the value of [[DateValue]] is - undefined, then -
      -
    1. Set the [[DateValue]] internal slot of O to - the time value (UTC) identifying the current time.
      2. -
    2. Return O.
      3. -
    -
    5. -
  5. Else, -
      -
    1. Let now be the Number that is the time value (UTC) - identifying the current time.
      2. -
    2. Return ToDateString (now).
      3. -
    -
    6. -
-
- -
-

20.3.2.4 new Date ( ...argumentsList )

- -

When Date is called as part of a new expression with argument list argumentsList it performs - the following steps:

- -
    -
  1. Let F be the Date function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return Construct (F, argumentsList).
    4. -
- -

If Date is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

20.3.3 Properties of the Date Constructor

- -

The value of the [[Prototype]] internal slot of the Date - constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 7), the Date constructor has the following - properties:

-
- -
-

20.3.3.1 - Date.now ( )

- -

The now function return a Number value that is the time - value designating the UTC date and time of the occurrence of the call to now.

-
- -
-

20.3.3.2 - Date.parse ( string )

- -

The parse function applies the ToString operator to its argument. If ToString results in an abrupt completion - the Completion Record is immediately returned. Otherwise, - parse interprets the resulting String as a date and time; it returns a Number, the UTC time value corresponding to the date and time. The String may be interpreted as - a local time, a UTC time, or a time in some other time zone, depending on the contents of the String. The function first - attempts to parse the format of the String according to the rules (including extended years) called out in Date Time - String Format (20.3.1.15). If the String does not conform to that format the - function may fall back to any implementation-specific heuristics or implementation-specific date formats. Unrecognizable - Strings or dates containing illegal element values in the format String shall cause Date.parse to return - NaN.

- -

If x is any Date object whose milliseconds amount is zero within a particular implementation of ECMAScript, - then all of the following expressions should produce the same numeric value in that implementation, if all the properties - referenced have their initial values:

- - 
x.valueOf()
- 
Date.parse(x.toString())
- 
Date.parse(x.toUTCString())
- 
Date.parse(x.toISOString())
- -

However, the expression

- - 
Date.parse(x.toLocaleString())
- -

is not required to produce the same Number value as the preceding three expressions and, in general, the value produced - by Date.parse is implementation-dependent when given any String value that does not conform to the Date Time - String Format (20.3.1.15) and that could not be produced in that implementation - by the toString or toUTCString method.

-
- -
-

20.3.3.3 - Date.prototype

- -

The initial value of Date.prototype is the built-in Date prototype object (20.3.4).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

20.3.3.4 - Date.UTC ( year, month [ , date [ , hours [ , minutes [ , seconds [ , ms ] ] ] ] ] )

- -

When the UTC function is called with fewer than two arguments, the behaviour is implementation-dependent. - When the UTC function is called with two to seven arguments, it computes the date from year, - month and (optionally) date, hours, minutes, seconds and - ms. The following steps are taken:

- -
    -
  1. Let y be ToNumber(year).
    2. -
  2. ReturnIfAbrupt(y).
    3. -
  3. Let m be ToNumber(month).
    4. -
  4. ReturnIfAbrupt(m).
    5. -
  5. If date is supplied then let dt be ToNumber(date); else let - dt be 1.
    6. -
  6. ReturnIfAbrupt(dt).
    7. -
  7. If hours is supplied then let h be ToNumber(hours); else let - h be 0.
    8. -
  8. ReturnIfAbrupt(h).
    9. -
  9. If minutes is supplied then let min be ToNumber(minutes); else let - min be 0.
    10. -
  10. ReturnIfAbrupt(min).
    11. -
  11. If seconds is supplied then let s be ToNumber(seconds); else let - s be 0.
    12. -
  12. ReturnIfAbrupt(s).
    13. -
  13. If ms is supplied then let milli be ToNumber(ms); else let - milli be 0.
    14. -
  14. ReturnIfAbrupt(milli).
    15. -
  15. If y is not NaN and 0 ≤ ToInteger(y) ≤ 99, then let yr be 1900+ToInteger(y); otherwise, let yr be y.
    16. -
  16. Return TimeClip(MakeDate(MakeDay(yr, m, dt), MakeTime(h, - min, s, milli))).
    17. -
- -

The length property of the UTC function is 7.

- -
-

NOTE The UTC function differs from the Date constructor in two - ways: it returns a time value as a Number, rather than creating a Date - object, and it interprets the arguments in UTC rather than as local time.

-
-
- -
-

20.3.3.5 - Date[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let obj be OrdinaryCreateFromConstructor(F, - "%DatePrototype%", ( [[DateValue]])).
    2. -
  2. Return obj.
    3. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE [[DateValue]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the Date constructor. This flag value is never directly exposed to - ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

20.3.4 Properties of the Date Prototype Object

- -

The Date prototype object is itself an ordinary object. It is not a Date instance and does not have a [[DateValue]] internal slot.

- -

The value of the [[Prototype]] internal slot of the Date - prototype object is the standard built-in Object prototype object (20.3.4).

- -

Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not generic and the - this value passed to them must be an object that has a [[DateValue]] internal slot that has been initialized to a time value.

- -

The abstract operation thisTimeValue(value) performs the - following steps:

- -
    -
  1. If Type(value) is Object and value has a - [[DateValue]] internal slot, then -
      -
    1. Let n be the value of value’s [[DateValue]] internal slot.
      2. -
    2. If n is not undefined, then return n.
      3. -
    -
    2. -
  2. Throw a TypeError exception.
    3. -
- -

In following descriptions of functions that are properties of the Date prototype object, the phrase “this Date - object” refers to the object that is the this value for the invocation of the function. The phrase - “this time value” within the specification of a method refers to - the result returned by calling the abstract operation thisTimeValue - with the this value of the method invocation passed as the argument.

-
- -
-

20.3.4.1 Date.prototype.constructor

- -

The initial value of Date.prototype.constructor is the built-in Date constructor.

-
- -
-

20.3.4.2 Date.prototype.getDate ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return DateFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.3 Date.prototype.getDay ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return WeekDay(LocalTime(t)).
    5. -
-
- -
-

20.3.4.4 Date.prototype.getFullYear ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return YearFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.5 Date.prototype.getHours ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return HourFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.6 Date.prototype.getMilliseconds ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return msFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.7 Date.prototype.getMinutes ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return MinFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.8 Date.prototype.getMonth ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return MonthFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.9 Date.prototype.getSeconds ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return SecFromTime(LocalTime(t)).
    5. -
-
- -
-

20.3.4.10 Date.prototype.getTime ( )

-
    -
  1. Return this time value.
    2. -
-
- -
-

20.3.4.11 Date.prototype.getTimezoneOffset ( )

- -

Returns the difference between local time and UTC time in minutes.

- -
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return (t − LocalTime(t)) / msPerMinute.
    5. -
-
- -
-

20.3.4.12 Date.prototype.getUTCDate ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return DateFromTime(t).
    5. -
-
- -
-

20.3.4.13 Date.prototype.getUTCDay ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return WeekDay(t).
    5. -
-
- -
-

20.3.4.14 Date.prototype.getUTCFullYear ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return YearFromTime(t).
    5. -
-
- -
-

20.3.4.15 Date.prototype.getUTCHours ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return HourFromTime(t).
    5. -
-
- -
-

20.3.4.16 Date.prototype.getUTCMilliseconds ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return msFromTime(t).
    5. -
-
- -
-

20.3.4.17 Date.prototype.getUTCMinutes ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return MinFromTime(t).
    5. -
-
- -
-

20.3.4.18 Date.prototype.getUTCMonth ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return MonthFromTime(t).
    5. -
-
- -
-

20.3.4.19 Date.prototype.getUTCSeconds ( )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return SecFromTime(t).
    5. -
-
- -
-

20.3.4.20 Date.prototype.setDate ( date )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let dt be ToNumber(date).
    3. -
  3. Let newDate be MakeDate(MakeDay(YearFromTime(t), MonthFromTime(t), - dt), TimeWithinDay(t)).
    4. -
  4. Let u be TimeClip(UTC(newDate)).
    5. -
  5. Set the [[DateValue]] internal slot of this Date - object to u.
    6. -
  6. Return u.
    7. -
-
- -
-

20.3.4.21 Date.prototype.setFullYear ( year [ , month [ , date ] ] )

-
    -
  1. Let t be the result of LocalTime(this time value); but if this time value is NaN, let t be - +0.
    2. -
  2. Let y be ToNumber(year).
    3. -
  3. If month is not specified, then let m be MonthFromTime(t); - otherwise, let m be ToNumber(month).
    4. -
  4. If date is not specified, then let dt be DateFromTime(t); - otherwise, let dt be ToNumber(date).
    5. -
  5. Let newDate be MakeDate(MakeDay(y, m, - dt), TimeWithinDay(t)).
    6. -
  6. Let u be TimeClip(UTC(newDate)).
    7. -
  7. Set the [[DateValue]] internal slot of this Date - object to u.
    8. -
  8. Return u.
    9. -
- -

The length property of the setFullYear method is 3.

- -
-

NOTE If month is not specified, this method behaves as if month were specified - with the value getMonth(). If date is not specified, it behaves as if date were specified - with the value getDate().

-
-
- -
-

20.3.4.22 Date.prototype.setHours ( hour [ , min [ , sec [ , ms ] ] ] )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let h be ToNumber(hour).
    3. -
  3. If min is not specified, then let m be MinFromTime(t); otherwise, let m be ToNumber(min).
    4. -
  4. If sec is not specified, then let s be SecFromTime(t); otherwise, let s be ToNumber(sec).
    5. -
  5. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    6. -
  6. Let date be MakeDate(Day(t), MakeTime(h, - m, s, milli)).
    7. -
  7. Let u be TimeClip(UTC(date)).
    8. -
  8. Set the [[DateValue]] internal slot of this Date - object to u.
    9. -
  9. Return u.
    10. -
- -

The length property of the setHours method is 4.

- -
-

NOTE If min is not specified, this method behaves as if min were specified with - the value getMinutes(). If sec is not specified, it behaves as if sec were specified with the - value getSeconds(). If ms is not specified, it behaves as if ms were specified with the value - getMilliseconds().

-
-
- -
-

20.3.4.23 Date.prototype.setMilliseconds ( ms )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let time be MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), ToNumber(ms)).
    3. -
  3. Let u be TimeClip(UTC(MakeDate(Day(t), - time))).
    4. -
  4. Set the [[DateValue]] internal slot of this Date - object to u.
    5. -
  5. Return u.
    6. -
-
- -
-

20.3.4.24 Date.prototype.setMinutes ( min [ , sec [ , ms ] ] )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let m be ToNumber(min).
    3. -
  3. If sec is not specified, then let s be SecFromTime(t); otherwise, let s be ToNumber(sec).
    4. -
  4. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    5. -
  5. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), m, s, - milli)).
    6. -
  6. Let u be TimeClip(UTC(date)).
    7. -
  7. Set the [[DateValue]] internal slot of this Date - object to u.
    8. -
  8. Return u.
    9. -
- -

The length property of the setMinutes method is 3.

- -
-

NOTE If sec is not specified, this method behaves as if sec were specified with - the value getSeconds(). If ms is not specified, this behaves as if ms were specified with the - value getMilliseconds().

-
-
- -
-

20.3.4.25 Date.prototype.setMonth ( month [ , date ] )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let m be ToNumber(month).
    3. -
  3. If date is not specified, then let dt be DateFromTime(t); - otherwise, let dt be ToNumber(date).
    4. -
  4. Let newDate be MakeDate(MakeDay(YearFromTime(t), m, dt), TimeWithinDay(t)).
    5. -
  5. Let u be TimeClip(UTC(newDate)).
    6. -
  6. Set the [[DateValue]] internal slot of this Date - object to u.
    7. -
  7. Return u.
    8. -
- -

The length property of the setMonth method is 2.

- -
-

NOTE If date is not specified, this method behaves as if date were specified - with the value getDate().

-
-
- -
-

20.3.4.26 Date.prototype.setSeconds ( sec [ , ms ] )

-
    -
  1. Let t be the result of LocalTime(this time value).
    2. -
  2. Let s be ToNumber(sec).
    3. -
  3. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    4. -
  4. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), MinFromTime(t), s, milli)).
    5. -
  5. Let u be TimeClip(UTC(date)).
    6. -
  6. Set the [[DateValue]] internal slot of this Date - object to u.
    7. -
  7. Return u.
    8. -
- -

The length property of the setSeconds method is 2.

- -
-

NOTE If ms is not specified, this method behaves as if ms were specified with - the value getMilliseconds().

-
-
- -
-

20.3.4.27 Date.prototype.setTime ( time )

-
    -
  1. Let v be TimeClip(ToNumber(time)).
    2. -
  2. ReturnIfAbrupt(v).
    3. -
  3. Set the [[DateValue]] internal slot of this Date - object to v.
    4. -
  4. Return v.
    5. -
-
- -
-

20.3.4.28 Date.prototype.setUTCDate ( date )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let dt be ToNumber(date).
    4. -
  4. Let newDate be MakeDate(MakeDay(YearFromTime(t), MonthFromTime(t), - dt), TimeWithinDay(t)).
    5. -
  5. Let v be TimeClip(newDate).
    6. -
  6. Set the [[DateValue]] internal slot of this Date - object to v.
    7. -
  7. Return v.
    8. -
-
- -
-

20.3.4.29 Date.prototype.setUTCFullYear ( year [ , month [ , date ] ] )

-
    -
  1. Let t be this time value; but if this time value is NaN, let t be - +0.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let y be ToNumber(year).
    4. -
  4. If month is not specified, then let m be MonthFromTime(t); - otherwise, let m be ToNumber(month).
    5. -
  5. If date is not specified, then let dt be DateFromTime(t); - otherwise, let dt be ToNumber(date).
    6. -
  6. Let newDate be MakeDate(MakeDay(y, m, - dt), TimeWithinDay(t)).
    7. -
  7. Let v be TimeClip(newDate).
    8. -
  8. Set the [[DateValue]] internal slot of this Date - object to v.
    9. -
  9. Return v.
    10. -
- -

The length property of the setUTCFullYear method is 3.

- -
-

NOTE If month is not specified, this method behaves as if month were specified - with the value getUTCMonth(). If date is not specified, it behaves as if date were specified - with the value getUTCDate().

-
-
- -
-

20.3.4.30 Date.prototype.setUTCHours ( hour [ , min [ , sec [ , ms ] ] ] - )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let h be ToNumber(hour).
    4. -
  4. If min is not specified, then let m be MinFromTime(t); otherwise, let m be ToNumber(min).
    5. -
  5. If sec is not specified, then let s be SecFromTime(t); otherwise, let s be ToNumber(sec).
    6. -
  6. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    7. -
  7. Let newDate be MakeDate(Day(t), MakeTime(h, - m, s, milli)).
    8. -
  8. Let v be TimeClip(newDate).
    9. -
  9. Set the [[DateValue]] internal slot of this Date - object to v.
    10. -
  10. Return v.
    11. -
- -

The length property of the setUTCHours method is 4.

- -
-

NOTE If min is not specified, this method behaves as if min were specified with - the value getUTCMinutes(). If sec is not specified, it behaves as if sec were specified with - the value getUTCSeconds(). If ms is not specified, it behaves as if ms were specified with - the value getUTCMilliseconds().

-
-
- -
-

20.3.4.31 Date.prototype.setUTCMilliseconds ( ms )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let time be MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), ToNumber(ms)).
    4. -
  4. Let v be TimeClip(MakeDate(Day(t), time)).
    5. -
  5. Set the [[DateValue]] internal slot of this Date - object to v.
    6. -
  6. Return v.
    7. -
-
- -
-

20.3.4.32 Date.prototype.setUTCMinutes ( min [ , sec [, ms ] ] )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let m be ToNumber(min).
    4. -
  4. If sec is not specified, then let s be SecFromTime(t); otherwise, let s be ToNumber(sec).
    5. -
  5. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    6. -
  6. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), m, s, - milli)).
    7. -
  7. Let v be TimeClip(date).
    8. -
  8. Set the [[DateValue]] internal slot of this Date - object to v.
    9. -
  9. Return v.
    10. -
- -

The length property of the setUTCMinutes method is 3.

- -
-

NOTE If sec is not specified, this method behaves as if sec were specified with - the value getUTCSeconds(). If ms is not specified, it function behaves as if ms were - specified with the value return by getUTCMilliseconds().

-
-
- -
-

20.3.4.33 Date.prototype.setUTCMonth ( month [ , date ] )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let m be ToNumber(month).
    4. -
  4. If date is not specified, then let dt be DateFromTime(t); - otherwise, let dt be ToNumber(date).
    5. -
  5. Let newDate be MakeDate(MakeDay(YearFromTime(t), m, dt), TimeWithinDay(t)).
    6. -
  6. Let v be TimeClip(newDate).
    7. -
  7. Set the [[DateValue]] internal slot of this Date - object to v.
    8. -
  8. Return v.
    9. -
- -

The length property of the setUTCMonth method is 2.

- -
-

NOTE If date is not specified, this method behaves as if date were specified - with the value getUTCDate().

-
-
- -
-

20.3.4.34 Date.prototype.setUTCSeconds ( sec [ , ms ] )

-
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. Let s be ToNumber(sec).
    4. -
  4. If ms is not specified, then let milli be msFromTime(t); otherwise, let milli be ToNumber(ms).
    5. -
  5. Let date be MakeDate(Day(t), MakeTime(HourFromTime(t), MinFromTime(t), s, milli)).
    6. -
  6. Let v be TimeClip(date).
    7. -
  7. Set the [[DateValue]] internal slot of this Date - object to v.
    8. -
  8. Return v.
    9. -
- -

The length property of the setUTCSeconds method is 2.

- -
-

NOTE If ms is not specified, this methold behaves as if ms were specified with - the value getUTCMilliseconds().

-
-
- -
-

20.3.4.35 Date.prototype.toDateString ( )

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent the “date” portion of the Date in the current time zone in a convenient, human-readable form.

-
- -
-

20.3.4.36 Date.prototype.toISOString ( )

- -

This function returns a String value representing the instance in time corresponding to this time value. The format of the String is the Date Time string - format defined in 20.3.1.15. All fields are present in the String. The time - zone is always UTC, denoted by the suffix Z. If this time value - is not a finite Number or if the year is not a value that can be represented in that format (if necessary using extended - year format), a RangeError exception is thrown.

-
- -
-

20.3.4.37 Date.prototype.toJSON ( key )

- -

This function provides a String representation of a Date object for use by JSON.stringify (24.3.2).

- -

When the toJSON method is called with argument key, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject, giving it the this value as its - argument.
    2. -
  2. Let tv be ToPrimitive(O, hint Number).
    3. -
  3. If tv is a Number and is not finite, return null.
    4. -
  4. Return Invoke(O, "toISOString").
    5. -
- -
-

NOTE 1 The argument is ignored.

-
- -
-

NOTE 2 The toJSON function is intentionally generic; it does not require that - its this value be a Date object. Therefore, it can be transferred to other kinds of objects for use as a method. - However, it does require that any such object have a toISOString method.

-
-
- -
-

20.3.4.38 Date.prototype.toLocaleDateString ( [ reserved1 [ , reserved2 ] ] - )

- -

An ECMAScript implementation that includes the ECMA-402 International API must implement the - Date.prototype.toLocaleDateString method as specified in the ECMA-402 specification. If an ECMAScript - implementation does not include the ECMA-402 API the following specification of the toLocaleDateString - method is used.

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent the “date” portion of the Date in the current time zone in a convenient, human-readable form that - corresponds to the conventions of the host environment’s current locale.

- -

The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that - do not include ECMA-402 support must not use those parameter position for anything else.

- -

The length property of the toLocaleDateString method is 0.

-
- -
-

20.3.4.39 Date.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )

- -

An ECMAScript implementation that includes the ECMA-402 International API must implement the - Date.prototype.toLocaleString method as specified in the ECMA-402 specification. If an ECMAScript - implementation does not include the ECMA-402 API the following specification of the toLocaleString method is - used.

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of - the host environment’s current locale.

- -

The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that - do not include ECMA-402 support must not use those parameter position for anything else.

- -

The length property of the toLocaleString method is 0.

-
- -
-

20.3.4.40 Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] - )

- -

An ECMAScript implementation that includes the ECMA-402 International API must implement the - Date.prototype.toLocaleTimeString method as specified in the ECMA-402 specification. If an ECMAScript - implementation does not include the ECMA-402 API the following specification of the toLocaleString method is - used.

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent the “time” portion of the Date in the current time zone in a convenient, human-readable form that - corresponds to the conventions of the host environment’s current locale.

- -

The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that - do not include ECMA-402 support must not use those parameter position for anything else.

- -

The length property of the toLocaleTimeString method is 0.

-
- -
-
-

20.3.4.41 Date.prototype.toString ( )

- -

The following steps are performed:

- -
    -
  1. Let tv be this time value.
    2. -
  2. Return ToDateString(tv).
    3. -
- -
-

NOTE For any Date object d whose - milliseconds amount is zero, the result of Date.parse(d.toString()) - is equal to d.valueOf(). See 20.3.3.2.

-
-
- -
-

20.3.4.41.1 Runtime Semantics: ToDateString(tv) Abstract Operation

-
    -
  1. Assert: Type(tv) is Number.
    2. -
  2. If tv is NaN, then return "Invalid Date".
    3. -
  3. Return an implementation-dependent String value that represents tv as a date and time in the current time - zone using a convenient, human-readable form.
    4. -
-
-
- -
-

20.3.4.42 Date.prototype.toTimeString ( )

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent the “time” portion of the Date in the current time zone in a convenient, human-readable form.

-
- -
-

20.3.4.43 Date.prototype.toUTCString ( )

- -

This function returns a String value. The contents of the String are implementation-dependent, but are intended to - represent this time value in a convenient, human-readable form - in UTC.

- -
-

NOTE The intent is to produce a String representation of a date that is more readable than - the format specified in 20.3.1.15. It is not essential that the chosen format - be unambiguous or easily machine parsable. If an implementation does not have a preferred human-readable format it is - recommended to use the format defined in 20.3.1.15 but with a space rather - than a “T” used to separate the date and time elements.

-
-
- -
-

20.3.4.44 Date.prototype.valueOf ( )

- -

The valueOf function returns a Number, which is this time value.

-
- -
-

20.3.4.45 Date.prototype [ @@toPrimitive ] ( hint )

- -

This function is called by ECMAScript language operators to convert an object to a primitive value. The allowed values - for hint are "default", "number", and "string". Date objects, are - unique among built-in ECMAScript object in that they treat "default" as being equivalent to - "string", All other built-in ECMAScript objects treat "default" as being equivalent to - "number".

- -

When the @@toPrimitive method is called with argument hint, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, then throw a TypeError - exception.
    3. -
  3. If hint is the string value "string" or the string value "default" , then -
      -
    1. Let tryFirst be "string".
      2. -
    -
    4. -
  4. Else if hint is the string value "number", then -
      -
    1. Let tryFirst be "number".
      2. -
    -
    5. -
  5. Else, throw a TypeError exception.
    6. -
  6. Return the result of OrdinaryToPrimitive(O, tryFirst).
    7. -
- -

The value of the name property of this function is "[Symbol.toPrimitive]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

20.3.5 Properties of Date Instances

- -

Date instances are ordinary objects that inherit properties from the Date prototype object. Date instances also have a - [[DateValue]] internal slot. The [[DateValue]] internal slot is the time value represented by this Date object.

-
-
-
- -
-
-

21 Text - Processing

-
- -
-
-

21.1 String - Objects

-
- -
-
-

21.1.1 - The String Constructor

- -

The String constructor is the %String% intrinsic object and the initial value of the String property of - the global object. When String is called as a function rather than as a constructor, it performs a type - conversion. However, if the this value passed in the call is an Object with an uninitialized [[StringData]] internal slot, it initializes the this value using the - argument value. This permits String to be used both to perform type conversion and to perform constructor - instance initialization.

- -

The String constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - String behaviour must include a super call to the String constructor to initialize - the [[StringData]] state of subclass instances.

-
- -
-

21.1.1.1 String ( value )

- -

When String is called with argument value, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If no arguments were passed to this function invocation, then let s be "".
    3. -
  3. Else, let s be ToString(value).
    4. -
  4. ReturnIfAbrupt(s).
    5. -
  5. If Type(O) is Object and O has a [[StringData]] internal slot and the value of [[StringData]] is - undefined, then -
      -
    1. Let length be the number of code unit elements in s.
      2. -
    2. Let status be the result of DefinePropertyOrThrow(O, - "length", PropertyDescriptor{[[Value]]: length, [[Writable]]: false, [[Enumerable]]: - false, [[Configurable]]: false }).
      3. -
    3. ReturnIfAbrupt(status).
      4. -
    4. Set the value of O’s [[StringData]] internal slot to s.
      5. -
    5. Return O.
      6. -
    -
    6. -
  6. Return s.
    7. -
- -

The length property of the String function is 1.

-
- -
-

21.1.1.2 new String ( ...argumentsList )

- -

When String is called as part of a new expression , it initializes a newly created exotic String - object:

- -
    -
  1. Let F be the String function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If String is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

21.1.2 Properties of the String Constructor

- -

The value of the [[Prototype]] internal slot of the - String constructor is the standard built-in Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the String constructor has the following - properties:

-
- -
-

21.1.2.1 String.fromCharCode ( ...codeUnits )

- -

The String.fromCharCode function may be called with any number of arguments which form the rest parameter - codeUnits. The following steps are taken:

- -
    -
  1. Let codeUnits is be a List containing the arguments - passed to this function.
    2. -
  2. Let length be the number of elements in codeUnits.
    3. -
  3. Let elements be a new List.
    4. -
  4. Let nextIndex be 0.
    5. -
  5. Repeat while nextIndex < length -
      -
    1. Let next be codeUnits[nextIndex].
      2. -
    2. Let nextCU be ToUint16(next).
      3. -
    3. ReturnIfAbrupt(nextCU).
      4. -
    4. Append nextCU to the end of elements.
      5. -
    5. Let nextIndex be nextIndex + 1.
      6. -
    -
    6. -
  6. Return the String value whose elements are, in order, the elements in the List elements. If length is 0, the empty string is - returned.
    7. -
- -

The length property of the fromCharCode function is 1.

-
- -
-

21.1.2.2 String.fromCodePoint ( ...codePoints )

- -

The String.fromCodePoint function may be called with any number of arguments which form the rest parameter - codePoints. The following steps are taken:

- -
    -
  1. Let codePoints be a List containing the arguments - passed to this function.
    2. -
  2. Let length be number of elements in codePoints.
    3. -
  3. Let elements be a new List.
    4. -
  4. Let nextIndex be 0.
    5. -
  5. Repeat while nextIndex < length -
      -
    1. Let next be codePoints[nextIndex].
      2. -
    2. Let nextCP be ToNumber(next).
      3. -
    3. ReturnIfAbrupt(nextCP).
      4. -
    4. If SameValue(nextCP, ToInteger(nextCP)) - is false, then throw a RangeError exception.
      5. -
    5. If nextCP < 0 or nextCP > 0x10FFFF, then throw a RangeError exception.
      6. -
    6. Append the elements of the UTF-16Encoding (10.1.1) of nextCP to the end of elements.
      7. -
    7. Let nextIndex be nextIndex + 1.
      8. -
    -
    6. -
  6. Return the String value whose elements are, in order, the elements in the List elements. If length is 0, the empty string is - returned.
    7. -
- -

The length property of the fromCodePoint function is 1.

-
- -
-

21.1.2.3 String.prototype

- -

The initial value of String.prototype is the standard built-in String prototype object (21.1.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

21.1.2.4 - String.raw ( callSite , ...substitutions )

- -

The String.raw function may be called with a variable number of arguments. The first argument is - callSite and the remainder of the arguments form the List - substitutions. The following steps are taken:

- -
    -
  1. Let substitutions be a List consisting of all of the - arguments passed to this function, starting with the second argument. If fewer than two arguments were passed, the - List is empty.
    2. -
  2. Let numberOfSubstitutions be the numer of elements in substitutions.
    3. -
  3. Let cooked be ToObject(callSite).
    4. -
  4. ReturnIfAbrupt(cooked).
    5. -
  5. Let rawValue be the result of Get(cooked, - "raw").
    6. -
  6. Let raw be ToObject(rawValue).
    7. -
  7. ReturnIfAbrupt(raw).
    8. -
  8. Let len be the result of Get(raw, "length").
    9. -
  9. Let literalSegments be ToLength(len).
    10. -
  10. ReturnIfAbrupt(literalSegments).
    11. -
  11. If literalSegments ≤ 0, then return the empty string.
    12. -
  12. Let stringElements be a new List.
    13. -
  13. Let nextIndex be 0.
    14. -
  14. Repeat -
      -
    1. Let nextKey be ToString(nextIndex).
      2. -
    2. Let next be the result of Get(raw, nextKey).
      3. -
    3. Let nextSeg be ToString(next).
      4. -
    4. ReturnIfAbrupt(nextSeg).
      5. -
    5. Append in order the code unit elements of nextSeg to the end of stringElements.
      6. -
    6. If nextIndex + 1 = literalSegments, then -
        -
      1. Return the string value whose elements are, in order, the elements in the List stringElements. If stringElements has - no elements, the empty string is returned.
        2. -
      -
      7. -
    7. If nextIndex< numberOfSubstitutions, then let next be - substitutions[nextIndex].
      8. -
    8. Else, let next is the empty String.
      9. -
    9. Let nextSub be ToString(next).
      10. -
    10. ReturnIfAbrupt(nextSub).
      11. -
    11. Append in order the code unit elements of nextSub to the end of stringElements.
      12. -
    12. Let nextIndex be nextIndex + 1.
      13. -
    -
    15. -
- -

The length property of the raw function is 1.

- -
-

NOTE String.raw is intended for use as a tag function of a Tagged Template String (12.3.7). When called as such the first argument will be a well formed template call - site object and the rest parameter will contain the substitution values.

-
-
- -
-

21.1.2.5 - String[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let proto be the result of GetPrototypeFromConstructor(F, - "%StringPrototype%").
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Let obj be the result of calling StringCreate (proto).
    5. -
  5. Return obj.
    6. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

- -
-

NOTE [[StringData]] is initially assigned the value undefined as a flag to indicate - that the instance has not yet been initialized by the String constructor. This flag value is never directly exposed to - ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
-
- -
-
-

21.1.3 Properties of the String Prototype Object

- -

The String prototype object is itself an ordinary object. It is not a String instance and does not have a - [[StringData]] internal slot.

- -

The value of the [[Prototype]] internal slot of the - String prototype object is the standard built-in Object prototype object (19.1.3).

- -

Unless explicitly stated otherwise, the methods of the String prototype object defined below are not generic and the - this value passed to them must be either a String value or an object that has a [[StringData]] internal slot that has been initialized to a String value.

- -

The abstract operation thisStringValue(value) performs the - following steps:

- -
    -
  1. If Type(value) is String, return value.
    2. -
  2. If Type(value) is Object and value has a - [[StringData]] internal slot, then -
      -
    1. Let s be the value of value’s [[StringData]] internal slot.
      2. -
    2. If s is not undefined, then return s.
      3. -
    -
    3. -
  3. Throw a TypeError exception.
    4. -
- -

The phrase “this String value” within the specification of a method refers to the result returned by - calling the abstract operation thisStringValue with the this - value of the method invocation passed as the argument.

-
- -
-

21.1.3.1 String.prototype.charAt ( pos )

- -
-

NOTE Returns a single element String containing the code unit at element position pos - in the String value resulting from converting this object to a String. If there is no element at that position, the - result is the empty String. The result is a String value, not a String object.

- -

If pos is a value of Number type that is an integer, then the result of - x.charAt(pos) is equal to the result of - x.substring(pos, pos+1).

-
- -

When the charAt method is called with one argument pos, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let position be ToInteger(pos).
    5. -
  5. ReturnIfAbrupt(position).
    6. -
  6. Let size be the number of elements in S.
    7. -
  7. If position < 0 or position ≥ size, return the empty String.
    8. -
  8. Return a String of length 1, containing one code unit from S, namely the code unit at position - position, where the first (leftmost) code unit in S is considered to be at position 0, the next one at - position 1, and so on.
    9. -
- -
-

NOTE The charAt function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.2 String.prototype.charCodeAt ( pos )

- -
-

NOTE Returns a Number (a nonnegative integer less than 216) that is the code unit - value of the string element at position pos in the String resulting from converting this object to a String. If - there is no element at that position, the result is NaN.

-
- -

When the charCodeAt method is called with one argument pos, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let position be ToInteger(pos).
    5. -
  5. ReturnIfAbrupt(position).
    6. -
  6. Let size be the number of elements in S.
    7. -
  7. If position < 0 or position ≥ size, return NaN.
    8. -
  8. Return a value of Number type, whose value is the code unit value of the element at position position in the - String S, where the first (leftmost) element in S is considered to be at position 0, the next one at - position 1, and so on.
    9. -
- -
-

NOTE The charCodeAt function is intentionally generic; it does not require that - its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.3 String.prototype.codePointAt ( pos )

- -
-

NOTE Returns a nonnegative integer Number less than 1114112 (0x110000) that is the UTF-16 - encoded code point value starting at the string element at position pos in the String resulting from converting - this object to a String. If there is no element at that position, the result is undefined. If a valid UTF-16 - surrogate pair does not begin at pos, the result is the code unit at pos.

-
- -

When the codePointAt method is called with one argument pos, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let position be ToInteger(pos).
    5. -
  5. ReturnIfAbrupt(position).
    6. -
  6. Let size be the number of elements in S.
    7. -
  7. If position < 0 or position ≥ size, return undefined.
    8. -
  8. Let first be the code unit value of the element at index position in the String S.
    9. -
  9. If first < 0xD800 or first > 0xDBFF or position+1 = size, then return - first.
    10. -
  10. Let second be the code unit value of the element at index position+1 in the String S.
    11. -
  11. If second < 0xDC00 or second > 0xDFFF, then return first.
    12. -
  12. Return ((first – 0xD800) × 1024) + (second – 0xDC00) + 0x10000.
    13. -
- -
-

NOTE The codePointAt function is intentionally generic; it does not require that - its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.4 String.prototype.concat ( ...args )

- -
-

NOTE When the concat method is called it returns a String consisting of the - string elements of this object (converted to a String) followed by the string elements of each of the arguments - converted to a String. The result is a String value, not a String object.

-
- -

When the concat method is called with zero or more arguments the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let args be a List whose elements are the arguments - passed to this function.
    5. -
  5. Let R be S.
    6. -
  6. Repeat, while args is not empty -
      -
    1. Remove the first element from args and let next be the value of that element.
      2. -
    2. Let nextString be ToString(next)
      3. -
    3. ReturnIfAbrupt(nextString).
      4. -
    4. Let R be the String value consisting of the string elements in the previous value of R followed by - the string elements of nextString.
      5. -
    -
    7. -
  7. Return R.
    8. -
- -

The length property of the concat method is 1.

- -
-

NOTE The concat function is intentionally generic; it does not require that its - this value be a String object. Therefore it can be transferred to other kinds of objects for use as a method.

-
-
- -
-

21.1.3.5 String.prototype.constructor

- -

The initial value of String.prototype.constructor is the built-in String constructor.

-
- -
-

21.1.3.6 String.prototype.contains ( searchString [ , position ] )

- -

The contains method takes two arguments, searchString and position, and performs the following - steps:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. If Type(searchString) is Object, then -
      -
    1. Let isRegExp be HasProperty(searchString, @@isRegExp).
      2. -
    2. If isRegExp is true, then throw a TypeError exception.
      3. -
    -
    5. -
  5. Let searchStr be ToString(searchString).
    6. -
  6. ReturnIfAbrupt(searchStr).
    7. -
  7. Let pos be ToInteger(position). (If position is undefined, - this step produces the value 0).
    8. -
  8. ReturnIfAbrupt(pos).
    9. -
  9. Let len be the number of elements in S.
    10. -
  10. Let start be min(max(pos, 0), len).
    11. -
  11. Let searchLen be the number of elements in searchStr.
    12. -
  12. If there exists any integer k not smaller than start such that k + searchLen is not - greater than len, and for all nonnegative integers j less than searchLen, the character at - position k+j of S is the same as the character at position j of searchStr, return - true; but if there is no such integer k, return false.
    13. -
- -

The length property of the contains method is 1.

- -
-

NOTE 1 If searchString appears as a substring of the result of converting this object - to a String, at one or more positions that are greater than or equal to position, then return true; - otherwise, returns false. If position is undefined, 0 is assumed, so as to search all of the - String.

-
- -
-

NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow - future editions to define extends that allow such argument values.

-
- -
-

NOTE 3 The contains function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.7 String.prototype.endsWith ( searchString [ , endPosition] )

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. If Type(searchString) is Object, then -
      -
    1. Let isRegExp be HasProperty(searchString, @@isRegExp).
      2. -
    2. If isRegExp is true, then throw a TypeError exception.
      3. -
    -
    5. -
  5. Let searchStr be ToString(searchString).
    6. -
  6. ReturnIfAbrupt(searchStr).
    7. -
  7. Let len be the number of elements in S.
    8. -
  8. If endPosition is undefined, let pos be len, else let pos be ToInteger(endPosition).
    9. -
  9. ReturnIfAbrupt(pos).
    10. -
  10. Let end be min(max(pos, 0), len).
    11. -
  11. Let searchLength be the number of elements in searchStr.
    12. -
  12. Let start be end - searchLength.
    13. -
  13. If start is less than 0, return false.
    14. -
  14. If the searchLength sequence of elements of S starting at start is the same as the full element - sequence of searchStr, return true.
    15. -
  15. Otherwise, return false.
    16. -
- -

The length property of the endsWith method is 1.

- -
-

NOTE 1 Returns true if the sequence of elements of searchString converted to a - String is the same as the corresponding elements of this object (converted to a String) starting at endPosition - – length(this). Otherwise returns false.

-
- -
-

NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow - future editions to define extends that allow such argument values.

-
- -
-

NOTE 3 The endsWith function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.8 String.prototype.indexOf ( searchString [ , position ] )

- -
-

NOTE If searchString appears as a substring of the result of converting this object to - a String, at one or more positions that are greater than or equal to position, then the index of the smallest - such position is returned; otherwise, ‑1 is returned. If position is undefined, 0 is - assumed, so as to search all of the String.

-
- -

The indexOf method takes two arguments, searchString and position, and performs the - following steps:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let searchStr be ToString(searchString).
    5. -
  5. ReturnIfAbrupt(searchString).
    6. -
  6. Let pos be ToInteger(position). (If position is undefined, - this step produces the value 0).
    7. -
  7. ReturnIfAbrupt(pos).
    8. -
  8. Let len be the number of elements in S.
    9. -
  9. Let start be min(max(pos, 0), len).
    10. -
  10. Let searchLen be the number of elements in searchStr.
    11. -
  11. Return the smallest possible integer k not smaller than start such that k+ searchLen is - not greater than len, and for all nonnegative integers j less than searchLen, the code unit at - position k+j of S is the same as the code unit at position j of searchStr; but if - there is no such integer k, then return the value -1.
    12. -
- -

The length property of the indexOf method is 1.

- -
-

NOTE The indexOf function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.9 String.prototype.lastIndexOf ( searchString [ , position ] )

- -
-

NOTE If searchString appears as a substring of the result of converting this object to - a String at one or more positions that are smaller than or equal to position, then the index of the greatest such - position is returned; otherwise, ‑1 is returned. If position is undefined, the length - of the String value is assumed, so as to search all of the String.

-
- -

The lastIndexOf method takes two arguments, searchString and position, and performs - the following steps:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let searchStr be ToString(searchString).
    5. -
  5. ReturnIfAbrupt(searchString).
    6. -
  6. Let numPos be ToNumber(position). (If position is undefined, - this step produces the value NaN).
    7. -
  7. ReturnIfAbrupt(numPos).
    8. -
  8. If numPos is NaN, let pos be +∞; otherwise, let pos be ToInteger(numPos).
    9. -
  9. Let len be the number of elements in S.
    10. -
  10. Let start be min(max(pos, 0), len).
    11. -
  11. Let searchLen be the number of elements in searchStr.
    12. -
  12. Return the largest possible nonnegative integer k not larger than start such that k+ - searchLen is not greater than len, and for all nonnegative integers j less than - searchLen, the code unit at position k+j of S is the same as the code unit at position - j of searchStr; but if there is no such integer k, then return the value -1.
    13. -
- -

The length property of the lastIndexOf method is 1.

- -
-

NOTE The lastIndexOf function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.10 String.prototype.localeCompare ( that [, reserved1 [ , reserved2 ] ] - )

- -

An ECMAScript implementation that includes the ECMA-402 International API must implement the localeCompare - method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the - following specification of the localeCompare method is used.

- -

When the localeCompare method is called with argument that, it returns a Number other than - NaN that represents the result of a locale-sensitive String comparison of the this value (converted to a - String) with that (converted to a String). The two Strings are S and That. - The two Strings are compared in an implementation-defined fashion. The result is intended to order String values in the - sort order specified by the system default locale, and will be negative, zero, or positive, depending on whether - S comes before That in the sort order, the Strings are equal, or S comes - after That in the sort order, respectively.

- -

Before perform the comparisons the following steps are performed to prepare the Strings:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let That be ToString(that).
    5. -
  5. ReturnIfAbrupt(That).
    6. -
- -

The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; - implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter - position.

- -

The localeCompare method, if considered as a function of two arguments this and that, is - a consistent comparison function (as defined in 22.1.3.24) on the set of all - Strings.

- -

The actual return values are implementation-defined to permit implementers to encode additional information in the - value, but the function is required to define a total ordering on all Strings. If the implementation performs - language-sensitive comparisions it must return 0 when comparing Strings that are considered canonically - equivalent by the Unicode standard.

- -

If no language-sensitive comparison at all is available from the host environment, this function may perform a bitwise - comparison.

- -

The length property of the localeCompare method is 1.

- -
-

NOTE 1 The localeCompare method itself is not directly suitable as an argument - to Array.prototype.sort because the latter requires a function of - two arguments.

-
- -
-

NOTE 2 This function is intended to rely on whatever language-sensitive comparison - functionality is available to the ECMAScript environment from the host environment, and to compare according to the - rules of the host environment’s current locale. This function must treat Strings that are canonically equivalent - according to the Unicode standard as identical. It is also recommended that this function not honour Unicode - compatibility equivalences or decompositions. For a definition and discussion of canonical equivalence see the Unicode - Standard, chapters 2 and 3, as well as Unicode Annex #15, Unicode Normalization Forms and Unicode Technical Note #5 - Canonical Equivalence in Applications. Also see Unicode Technical Stardard #10, Unicode Collation Algorithm.

-
- -
-

NOTE 3 The localeCompare function is intentionally generic; it does not require - that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.11 String.prototype.match ( regexp )

- -

When the match method is called with argument regexp, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. If Type(regexp) is Object and HasProperty(regexp, @@isRegExp) is true, then let rx be - regexp;
    5. -
  5. Else, let rx be the result of the abstract operation RegExpCreate (21.2.3.3) with arguments regexp and - undefined.
    6. -
  6. ReturnIfAbrupt(rx).
    7. -
  7. Return the result of Invoke(rx, "match", ( S )). .
    8. -
- -
-

NOTE The match function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.12 String.prototype.normalize ( [ form ] )

- -

When the normalize method is called with one argument form, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. If form is not provided or form is undefined let form be - "NFC".
    5. -
  5. Let f be ToString(form).
    6. -
  6. ReturnIfAbrupt(f).
    7. -
  7. If f is not one of "NFC", "NFD", - "NFKC", or "NFKD", then throw a RangeError - Exception.
    8. -
  8. Let ns be the String value is the result of normalizing S into the normalization form named by - f as specified in Unicode Standard Annex #15, Unicode Normalization Forms.
    9. -
  9. Return ns.
    10. -
- -

The length property of the normalize method is 0.

- -
-

NOTE The normalize function is intentionally generic; it does not require that - its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.13 String.prototype.repeat ( count )

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let n be the result of calling ToInteger(count).
    5. -
  5. ReturnIfAbrupt(n).
    6. -
  6. If n < 0, then throw a RangeError exception.
    7. -
  7. If n is +∞, then throw a RangeError exception.
    8. -
  8. Let T be a String value that is made from n copies of S appended together. If n is 0, - T is the empty String.
    9. -
  9. Return T.
    10. -
- -
-

NOTE 1 This method creates a String consisting of the string elements of this object - (converted to String) repeated count times.

-
- -
-

NOTE 2 The repeat function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-
-

21.1.3.14 String.prototype.replace (searchValue, replaceValue )

- -

When the replace method is called with arguments searchValue and replaceValue the - following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let string be ToString(O).
    3. -
  3. ReturnIfAbrupt(string).
    4. -
  4. If Type(searchValue) is Object and HasProperty(searchValue, @@isRegExp) is true, then -
      -
    1. Return Invoke(searchValue, "replace", (string, - replaceValue)).
      2. -
    -
    5. -
  5. Let searchString be ToString(searchValue).
    6. -
  6. ReturnIfAbrupt(searchString).
    7. -
  7. Search string for the first occurrence of searchString and let pos be the index position - within string of the first code unit of the matched substring and let matched be - searchString. If no occurrences of searchString were found, return string.
    8. -
  8. If IsCallable(replaceValue) is true, then -
      -
    1. Let replValue be the result of calling the [[Call]] internal method of replaceValue passing - undefined as the this value and a List - containing matched, pos, and string as the argument list.
      2. -
    2. Let replStr be ToString(replValue).
      3. -
    3. ReturnIfAbrupt(replStr).
      4. -
    -
    9. -
  9. Else, -
      -
    1. Let captures be an empty List.
      2. -
    2. Let replacement be ToString(replaceValue).
      3. -
    3. ReturnIfAbrupt(replacement).
      4. -
    4. Let replStr be GetReplaceSubstitution(matched, - string, pos, captures, replacement).
      5. -
    -
    10. -
  10. Let tailPos be pos + the number of code units in matched.
    11. -
  11. Let newString be the String formed by concatenating the first pos code units of string, - replStr, and the trailing substring of string starting at index tailPos. If pos is 0, - the first element of the concatenation will be the empty String.
    12. -
  12. Return newString.
    13. -
- -
-

NOTE The replace function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.14.1 Runtime Semantics: GetReplaceSubstitution Abstract - Operation

- -

The abstract operation GetReplaceSubstitution(matched, string, position, captures, replacement) performs the following steps:

- -
    -
  1. Assert: Type(matched) is String.
    2. -
  2. Let matchLength be the number of code units in matched.
    3. -
  3. Assert: Type(string) is String.
    4. -
  4. Let stringLength be the number of code units in string.
    5. -
  5. Assert: position is a nonnegative integer.
    6. -
  6. Assert: position ≤ stringLength.
    7. -
  7. Assert: captures is a possibly empty List of Strings.
    8. -
  8. Assert:Type( - replacement) is String
    9. -
  9. Let tailPos be position + matchLength.
    10. -
  10. Let m be the number of elements in captures.
    11. -
  11. Let result be a String value derived from replacement by copying code unit elements from - replacement to result while performing replacements as specified in Table - 40. These $ replacements are done left-to-right, and, once such a replacement is performed, the - new replacement text is not subject to further replacements.
    12. -
  12. Return result.
    13. -
- -
-
Table 40 — Replacement Text Symbol Substitutions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Code unitsUnicode CharactersReplacement text
0x0024, 0x0024$$$
0x0024, 0x0026$&matched
0x0024, 0x0060$`If position is 0, the replacement is the empty String. Otherwise the replacement is the substring of string that starts at index 0 and whose last code point is at index position -1.
0x0024, 0x0027$'If tailPos ≥ stringLength, the replacement is the empty String. Otherwise the replacement is the substring of string that starts at index tailPos and continues to the end of string.
0x0024, N where
0x0031 ≤ N ≤ 0x0039		$n where
n is one of 1 2 3 4 5 6 7 8 9 and $n is not followed by a decimal digit		The nth element of captures, where n is a single digit in the range 1 to 9. If n≤m and the nth element of captures is undefined, use the empty String instead. If n>m, the result is implementation-defined.
0x0024, N, N where
0x0030 ≤ N ≤ 0x0039		$nn where
n is one of 0 1 2 3 4 5 6 7 8 9		The nnth element of captures, where nn is a two-digit decimal number in the range 01 to 99. If nn≤m and the nnth element of captures is undefined, use the empty String instead. If nn is 00 or nn>m, the result is implementation-defined.
0x0024$ in any context that does not match any of the above.$
-
-
-
- -
-

21.1.3.15 String.prototype.search ( regexp )

- -

When the search method is called with argument regexp, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let string be ToString(O).
    3. -
  3. ReturnIfAbrupt(string).
    4. -
  4. If Type(regexp) is Object and HasProperty(regexp, @@isRegExp) is true , then, -
      -
    1. Let rx be regexp;
      2. -
    -
    5. -
  5. Else, -
      -
    1. Let rx be the result of the abstract operation RegExpCreate (21.2.3.3) with arguments regexp and - undefined.
      2. -
    -
    6. -
  6. ReturnIfAbrupt(rx).
    7. -
  7. Return the result of Invoke(rx, "search", (string)).
    8. -
- -
-

NOTE The search function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.16 String.prototype.slice ( start, end )

- -

The slice method takes two arguments, start and end, and returns a substring of the - result of converting this object to a String, starting from element position start and running to, but not - including, element position end (or through the end of the String if end is undefined). If - start is negative, it is treated as sourceLength+start where sourceLength is the length of the String. If - end is negative, it is treated as sourceLength+end where sourceLength is the length of the String. The result is a - String value, not a String object. The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let len be the number of elements in S.
    5. -
  5. Let intStart be ToInteger(start).
    6. -
  6. If end is undefined, let intEnd be len; else let intEnd be ToInteger(end).
    7. -
  7. If intStart is negative, let from be max(len + intStart,0); else let from be - min(intStart, len).
    8. -
  8. If intEnd is negative, let to be max(len + intEnd,0); else let to be - min(intEnd, len).
    9. -
  9. Let span be max(to – from,0).
    10. -
  10. Return a String value containing span consecutive elements from S beginning with the element at - position from.
    11. -
- -

The length property of the slice method is 2.

- -
-

NOTE The slice function is intentionally generic; it does not require that its - this value be a String object. Therefore it can be transferred to other kinds of objects for use as a method.

-
-
- -
-
-

21.1.3.17 String.prototype.split ( separator, limit )

- -

Returns an Array object into which substrings of the result of converting this object to a String have been stored. - The substrings are determined by searching from left to right for occurrences of separator; these occurrences - are not part of any substring in the returned array, but serve to divide up the String value. The value of - separator may be a String of any length or it may be a RegExp object.

- -

When the split method is called, the following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. If Type(separator) is Object and HasProperty(separator, @@isRegExp) is true , then, -
      -
    1. Return the result of Invoke(separator, "split", (O, - limit))
      2. -
    -
    4. -
  4. Let S be ToString(O).
    5. -
  5. ReturnIfAbrupt(S).
    6. -
  6. Let A be the result of the abstract operation ArrayCreate with argument - 0.
    7. -
  7. Let lengthA be 0.
    8. -
  8. If limit is undefined, let lim = 253–1; else let lim = ToLength(limit).
    9. -
  9. Let s be the number of elements in S.
    10. -
  10. Let p = 0.
    11. -
  11. Let R be ToString(separator).
    12. -
  12. ReturnIfAbrupt(R).
    13. -
  13. If lim = 0, return A.
    14. -
  14. If separator is undefined, then -
      -
    1. Call CreateDataProperty(A, "0", - S).
      2. -
    2. Assert: The above call will never result in an abrupt completion.
      3. -
    3. Return A.
      4. -
    -
    15. -
  15. If s = 0, then -
      -
    1. Let z be the result of SplitMatch(S, 0, R).
      2. -
    2. If z is not false, return A.
      3. -
    3. Call CreateDataProperty(A, "0", - S).
      4. -
    4. Assert: The above call will never result in an abrupt completion.
      5. -
    5. Return A.
      6. -
    -
    16. -
  16. Let q = p.
    17. -
  17. Repeat, while q ≠ s -
      -
    1. Let e be the result of SplitMatch(S, q, R).
      2. -
    2. If e is false, then let q = q+1.
      3. -
    3. Else e is an integer index into S, -
        -
      1. If e = p, then let q = q+1.
        2. -
      2. Else e ≠ p, -
          -
        1. Let T be a String value equal to the substring of S consisting of the code units at - positions p (inclusive) through q (exclusive).
          2. -
        2. Call CreateDataProperty(A, ToString(lengthA), T).
          3. -
        3. Assert: The above call will never result in an abrupt completion.
          4. -
        4. Increment lengthA by 1.
          5. -
        5. If lengthA = lim, return A.
          6. -
        6. Let p = e.
          7. -
        7. Let q = p.
          8. -
        -
        3. -
      -
      4. -
    -
    18. -
  18. Let T be a String value equal to the substring of S consisting of the code units at positions - p (inclusive) through s (exclusive).
    19. -
  19. Call CreateDataProperty(A, ToString(lengthA), T).
    20. -
  20. Assert: The above call will never result in an abrupt completion.
    21. -
  21. Return A.
    22. -
- -
-

NOTE The value of separator may be an empty String, an empty regular expression, or - a regular expression that can match an empty String. In this case, separator does not match the empty substring - at the beginning or end of the input String, nor does it match the empty substring at the end of the previous - separator match. (For example, if separator is the empty String, the String is split up into individual code - unit elements; the length of the result array equals the length of the String, and each substring contains one code - unit.) If separator is a regular expression, only the first match at a given position of the this String - is considered, even if backtracking could yield a non-empty-substring match at that position. (For example, - "ab".split(/a*?/) evaluates to the array ["a","b"], while "ab".split(/a*/) - evaluates to the array["","b"].)

- -

If the this object is (or converts to) the empty String, the result depends on whether separator can - match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one - element, which is the empty String.

- -

If separator is a regular expression that contains capturing parentheses, then each time separator is - matched the results (including any undefined results) of the capturing parentheses are spliced into the output - array. For example,

- - 
"A<B>bold</B>and<CODE>coded</CODE>".split(/<(\/)?([^<>]+)>/)
- -

evaluates to the array

- - 
["A", undefined, "B", "bold", "/", "B", "and", undefined,
 "CODE", "coded", "/", "CODE", ""]
- -

If separator is undefined, then the result array contains just one String, which is the this - value (converted to a String). If limit is not undefined, then the output array is truncated so that it - contains no more than limit elements.

-
-
- -
-

21.1.3.17.1 Runtime Semantics: SplitMatch Abstract Operation

- -

The abstract operation SplitMatch takes three parameters, a String S, an integer q, and a - String R, and performs the following in order to return either false or the end index of a match:

- -
    -
  1. Type(R) must be String. Let r be the number of - code units in R.
    2. -
  2. Let s be the number of code units in S.
    3. -
  3. If q+r > s then return false.
    4. -
  4. If there exists an integer i between 0 (inclusive) and r (exclusive) such that the code unit at - position q+i of S is different from the code unit at position i of R, then - return false.
    5. -
  5. Return q+r.
    6. -
- -

The length property of the split method is 2.

- -
-

NOTE The split function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
-
- -
-

21.1.3.18 String.prototype.startsWith ( searchString [, position ] )

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. If Type(searchString) is Object, then -
      -
    1. Let isRegExp be HasProperty(searchString, @@isRegExp).
      2. -
    2. If isRegExp is true, then throw a TypeError exception.
      3. -
    -
    5. -
  5. Let searchStr be ToString(searchString).
    6. -
  6. Let pos be ToInteger(position). (If position is undefined, - this step produces the value 0).
    7. -
  7. ReturnIfAbrupt(pos).
    8. -
  8. Let len be the number of elements in S.
    9. -
  9. Let start be min(max(pos, 0), len).
    10. -
  10. Let searchLength be the number of elements in searchStr.
    11. -
  11. If searchLength+start is greater than len, return false.
    12. -
  12. If the searchLength sequence of elements of S starting at start is the same as the full element - sequence of searchStr, return true.
    13. -
  13. Otherwise, return false.
    14. -
- -

The length property of the startsWith method is 1.

- -
-

NOTE 1 This method returns true if the sequence of elements of searchString - converted to a String is the same as the corresponding elements of this object (converted to a String) starting at - position. Otherwise returns false.

-
- -
-

NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow - future editions to define extends that allow such argument values.

-
- -
-

NOTE 3 The startsWith function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.19 String.prototype.substring ( start, end )

- -

The substring method takes two arguments, start and end, and returns a substring of the - result of converting this object to a String, starting from element position start and running to, but not - including, element position end of the String (or through the end of the String is end is - undefined). The result is a String value, not a String object.

- -

If either argument is NaN or negative, it is replaced with zero; if either argument is larger than the length of - the String, it is replaced with the length of the String.

- -

If start is larger than end, they are swapped.

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let len be the number of elements in S.
    5. -
  5. Let intStart be ToInteger(start).
    6. -
  6. If end is undefined, let intEnd be len; else let intEnd be ToInteger(end).
    7. -
  7. Let finalStart be min(max(intStart, 0), len).
    8. -
  8. Let finalEnd be min(max(intEnd, 0), len).
    9. -
  9. Let from be min(finalStart, finalEnd).
    10. -
  10. Let to be max(finalStart, finalEnd).
    11. -
  11. Return a String whose length is to - from, containing code units from S, namely the code units - with indices from through to −1, in ascending order.
    12. -
- -

The length property of the substring method is 2.

- -
-

NOTE The substring function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.20 String.prototype.toLocaleLowerCase ( )

- -

This function interprets a string value as a sequence of code points, as described in 6.1.4.

- -

This function works exactly the same as toLowerCase except that its result is intended to yield the - correct result for the host environment’s current locale, rather than a locale-independent result. There will only - be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode - case mappings.

- -
-

NOTE 1 The first parameter to this function is likely to be used in a future version of this - standard; it is recommended that implementations do not use this parameter position for anything else.

-
- -
-

NOTE 2 The toLocaleLowerCase function is intentionally generic; it does not - require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for - use as a method.

-
-
- -
-

21.1.3.21 String.prototype.toLocaleUpperCase ( )

- -

This function interprets a string value as a sequence of code points, as described in 6.1.4.

- -

This function works exactly the same as toUpperCase except that its result is intended to yield the - correct result for the host environment’s current locale, rather than a locale-independent result. There will only - be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode - case mappings.

- -
-

NOTE 1 The first parameter to this function is likely to be used in a future version of this - standard; it is recommended that implementations do not use this parameter position for anything else.

-
- -
-

NOTE 2 The toLocaleUpperCase function is intentionally generic; it does not - require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for - use as a method.

-
-
- -
-

21.1.3.22 String.prototype.toLowerCase ( )

- -

This function interprets a string value as a sequence of code points, as described in 6.1.4. The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let cpList be a List containing in order the code - points as defined in 6.1.4 of S, starting at the - first element of S.
    5. -
  5. For each code point c in cpList, if the Unicode Character Database provides a language insensitive - lower case equivalent of c then replace c in cpList with that equivalent code point(s).
    6. -
  6. Let cuList be a new List.
    7. -
  7. For each code point c in cpList, in order, append to cuList the elements of the UTF-16Encoding (10.1.1) of c.
    8. -
  8. Let L be a String whose elements are, in order, the elements of cuList .
    9. -
  9. Return L.
    10. -
- -

The result must be derived according to the locale-insensitive case mappings in the Unicode Character - Database (this explicitly includes not only the UnicodeData.txt file, but also all locale-insensitive mappings in the - SpecialCasings.txt file that accompanies it).

- -
-

NOTE 1 The case mapping of some code points may produce multiple code points . In this case - the result String may not be the same length as the source String. Because both toUpperCase and - toLowerCase have context-sensitive behaviour, the functions are not symmetrical. In other words, - s.toUpperCase().toLowerCase() is not necessarily equal to s.toLowerCase().

-
- -
-

NOTE 2 The toLowerCase function is intentionally generic; it does not require - that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.23 String.prototype.toString ( )

- -

When the toString method is called, the following steps are taken:

- -
    -
  1. Let s be thisStringValue(this value).
    2. -
  2. Return s.
    3. -
- -
-

NOTE For a String object, the toString method happens to return the same thing - as the valueOf method.

-
-
- -
-

21.1.3.24 String.prototype.toUpperCase ( )

- -

This function interprets a string value as a sequence of code points, as described in 6.1.4.

- -

This function behaves in exactly the same way as String.prototype.toLowerCase, except that code points are mapped to - their uppercase equivalents as specified in the Unicode Character Database.

- -
-

NOTE The toUpperCase function is intentionally generic; it does not require that - its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.25 String.prototype.trim ( )

- -

This function interprets a string value as a sequence of code points, as described in 6.1.4.

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let T be a String value that is a copy of S with both leading and trailing white space removed. The - definition of white space is the union of WhiteSpace and LineTerminator. When determining whether a - Unicode code point is in Unicode general category “Zs”, code unit sequences are interpreted as UTF-16 - encoded code point sequences as specified in 6.1.4.
    5. -
  5. Return T.
    6. -
- -
-

NOTE The trim function is intentionally generic; it does not require that its - this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a - method.

-
-
- -
-

21.1.3.26 String.prototype.valueOf ( )

- -

When the valueOf method is called, the following steps are taken:

- -
    -
  1. Let s be thisStringValue(this value).
    2. -
  2. Return s.
    3. -
-
- -
-

21.1.3.27 String.prototype [ @@iterator ]( )

- -

When the @@iterator method is called it returns an Iterator object (25.1.2) that - iterates over the code points of a String value, returning each code point as a String value. The following steps are - taken:

- -

The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Return the result of calling the CreateStringIterator abstract operation - with argument S.
    5. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
-
- -
-
-

21.1.4 Properties of String Instances

- -

String instances are String exotic objects and have the internal methods specified for such objects. String instances - inherit properties from the String prototype object. String instances also have a [[StringData]] internal slot.

- -

String instances have a length property, and a set of enumerable properties with integer indexed - names.

-
- -
-

21.1.4.1 length

- -

The number of elements in the String value represented by this String object.

- -

Once a String object is initialized, this property is unchanging. It has the attributes { [[Writable]]: false, - [[Enumerable]]: false, [[Configurable]]: false }.

-
-
- -
-
-

21.1.5 String Iterator Objects

- -

An String Iterator is an object, that represents a specific iteration over some specific String instance object. There - is not a named constructor for String Iterator objects. Instead, String iterator objects are created by calling certain - methods of String instance objects.

-
- -
-

21.1.5.1 CreateStringIterator Abstract Operation

- -

Several methods of String objects return Iterator objects. The abstract operation CreateStringIterator with argument - string is used to create such iterator objects. It performs the following steps:

- -
    -
  1. Let s be the result of calling ToString(string).
    2. -
  2. ReturnIfAbrupt(s).
    3. -
  3. Let iterator be the result of ObjectCreate(%StringIteratorPrototype%, - ([[IteratedStringt]], [[StringIteratorNextIndex]] )).
    4. -
  4. Set iterator’s [[IteratedString]] internal - slot to s.
    5. -
  5. Set iterator’s [[StringIteratorNextIndex]] internal slot to 0.
    6. -
  6. Return iterator.
    7. -
-
- -
-
-

21.1.5.2 The %StringIteratorPrototype% Object

- -

All String Iterator Objects inherit properties from the %StringIteratorPrototype% intrinsic object. The - %StringIteratorPrototype% object is an ordinary object and its [[Prototype]] internal slot is the %ObjectPrototype% intrinsic object. In - addition, %StringIteratorPrototype% has the following properties:

-
- -
-

21.1.5.2.1 %StringIteratorPrototype%.next ( )

-
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have all of the internal slots of an String Iterator Instance (21.1.5.3), throw a TypeError exception.
    4. -
  4. Let s be the value of the [[IteratedString]] internal slot of O.
    5. -
  5. If s is undefined, then return CreateIterResultObject(undefined, true).
    6. -
  6. Let position be the value of the [[StringIteratorNextIndex]] internal slot of O.
    7. -
  7. Let len be the number of elements in s.
    8. -
  8. If position ≥ len, then -
      -
    1. Set the value of the [[IteratedString]] internal - slot of O to undefined.
      2. -
    2. Return CreateIterResultObject(undefined, true).
      3. -
    -
    9. -
  9. Let first be the code unit value of the element at index position in s.
    10. -
  10. If first < 0xD800 or first > 0xDBFF or position+1 = len, then let - resultString be the string consisting of the single code unit first.
    11. -
  11. Else, -
      -
    1. Let second be the code unit value of the element at index position+1 in the String - S.
      2. -
    2. If second < 0xDC00 or second > 0xDFFF, then let resultString be the string - consisting of the single code unit first.
      3. -
    3. Else, let resultString be the string consisting of the code unit first followed by the code unit - second.
      4. -
    -
    12. -
  12. Let resultSize be the number of code units in resultString.
    13. -
  13. Set the value of the [[StringIteratorNextIndex]] internal slot of O to position+ - resultSize.
    14. -
  14. Return CreateIterResultObject(resultString, false).
    15. -
-
- -
-

21.1.5.2.2 %StringIteratorPrototype% [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

21.1.5.2.3 %StringIteratorPrototype% [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "String Iterator".

-
-
- -
-

21.1.5.3 Properties of String Iterator Instances

- -

String Iterator instances are ordinary objects that inherit properties from the %StringIteratorPrototype% intrinsic - object. String Iterator instances are initially created with the internal slots listed in Table - 43.

- -
-
Table 41 — Internal Slots of String Iterator Instances
- - - - - - - - - - - - - -
Internal SlotDescription
[[IteratedString]]The String value whose elements are being iterated.
[[StringIteratorNextIndex]]The integer index of the next string index to be examined by this iteration.
-
-
-
-
- -
-
-

21.2 RegExp (Regular Expression) Objects

- -

A RegExp object contains a regular expression and the associated flags.

- -
-

NOTE The form and functionality of regular expressions is modelled after the regular expression - facility in the Perl 5 programming language.

-
-
- -
-

21.2.1 - Patterns

- -

The RegExp constructor applies the following grammar to the input pattern String. An error occurs if the - grammar cannot interpret the String as an expansion of Pattern.

- -

Syntax

- -
-
Pattern[U] ::
-
Disjunction[?U]
-
- -
-
Disjunction[U] ::
-
Alternative[?U]
-
Alternative[?U] | Disjunction[?U]
-
- -
-
Alternative[U] ::
-
[empty]
-
Alternative[?U] Term[?U]
-
- -
-
Term[U] ::
-
Assertion[?U]
-
Atom[?U]
-
Atom[?U] Quantifier
-
- -
-
Assertion[U] ::
-
^
-
$
-
\ b
-
\ B
-
( ? = Disjunction[?U] )
-
( ? ! Disjunction[?U] )
-
- -
-
Quantifier ::
-
QuantifierPrefix
-
QuantifierPrefix ?
-
- -
-
QuantifierPrefix ::
-
*
-
+
-
?
-
{ DecimalDigits }
-
{ DecimalDigits , }
-
{ DecimalDigits , DecimalDigits }
-
- -
-
Atom[U] ::
-
PatternCharacter
-
.
-
\ AtomEscape[?U]
-
CharacterClass[?U]
-
( Disjunction[?U] )
-
( ? : Disjunction[?U] )
-
- -
-
SyntaxCharacter :: one of
-
^ $ \ . * + ? ( ) [ ] { } |
-
- -
-
PatternCharacter ::
-
SourceCharacter but not SyntaxCharacter
-
- -
-
AtomEscape[U] ::
-
DecimalEscape
-
CharacterEscape[?U]
-
CharacterClassEscape
-
- -
-
CharacterEscape[U] ::
-
ControlEscape
-
c ControlLetter
-
HexEscapeSequence
-
RegExpUnicodeEscapeSequence[?U]
-
IdentityEscape[?U]
-
- -
-
ControlEscape :: one of
-
f n r t v
-
- -
-
ControlLetter :: one of
-
a b c d e f g h i j k l m n o p q r s t u v w x y z
-
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
-
- -
-
RegExpUnicodeEscapeSequence[U] ::
-
[+U] u LeadSurrogate \u TrailSurrogate
-
u Hex4Digits
-
[+U] u{ HexDigits }
-
- -
-
LeadSurrogate ::
-
Hex4Digits [match only if the CV of Hex4Digits is in the inclusive range 0xD800 to 0xDBFF]
-
- -
-
TrailSurrogate ::
-
Hex4Digits [match only if the CV of Hex4Digits is in the inclusive range 0xDC00 to 0xDFFF]
-
- -
-
IdentityEscape[U] ::
-
[+U] SyntaxCharacter
-
[~U] SourceCharacter but not IdentifierPart
-
[~U] <ZWJ>
-
[~U] <ZWNJ>
-
- -
-
DecimalEscape ::
-
DecimalIntegerLiteral [lookahead ∉ DecimalDigit]
-
- -
-
CharacterClassEscape :: one of
-
d D s S w W
-
- -
-
CharacterClass[U] ::
-
[ [lookahead ∉ {^}] ClassRanges[?U] ]
-
[ ^ ClassRanges[?U] ]
-
- -
-
ClassRanges[U] ::
-
[empty]
-
NonemptyClassRanges[?U]
-
- -
-
NonemptyClassRanges[U] ::
-
ClassAtom[?U]
-
ClassAtom[?U] NonemptyClassRangesNoDash[?U]
-
ClassAtom[?U] - ClassAtom[?U] ClassRanges[?U]
-
- -
-
NonemptyClassRangesNoDash[U] ::
-
ClassAtom[?U]
-
ClassAtomNoDash[?U] NonemptyClassRangesNoDash[?U]
-
ClassAtomNoDash[?U] - ClassAtom[?U] ClassRanges[?U]
-
- -
-
ClassAtom[U] ::
-
-
-
ClassAtomNoDash[?U]
-
- -
-
ClassAtomNoDash[U] ::
-
SourceCharacter but not one of \ or ] or -
-
\ ClassEscape[?U]
-
- -
-
ClassEscape[U] ::
-
DecimalEscape
-
b
-
CharacterEscape[?U]
-
CharacterClassEscape
-
-
- -
-
-

21.2.2 - Pattern Semantics

- -

A regular expression pattern is converted into an internal procedure using the process described below. An - implementation is encouraged to use more efficient algorithms than the ones listed below, as long as the results are the - same. The internal procedure is used as the value of a RegExp object’s [[RegExpMatcher]] internal slot.

- -

A Pattern is either a BMP pattern or a Unicode pattern depending upon whether or not its - associated flags contain an "u". A BMP pattern matches against a String interpreted as consisting of a - sequence of Unicode code units. A Unicode pattern matches against a String interpreted as consisting of Unicode code - points encoded using UTF-16. In the context of describing the behaviour of a BMP pattern “character” means a - Unicode code unit. In the context of describing the behaviour of a Unicode pattern “character” means a UTF-16 - code point. In either context, “character value” means the numeric value of the code unit or code point.

- -

The semantics of Pattern is defined as if a Pattern was a List of SourceCharacter values where each SourceCharacter corresponds to a Unicode code point. If a BMP pattern contains a non-BMP SourceCharacter the entire pattern is encoded using UTF-16 and the individual code units of that - encoding are used as the elements of the List.

- -
-

NOTE For example, consider a pattern expressed in source code as the single non-BMP character - U+1D11E (MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a - single element (character) List consisting of the single code - point 0x1D11E. However, interpreted as a BMP pattern, it is first UTF-16 encoded to produce a two element List consisting of the code units 0xD834 and 0xDD1E.

- -

Patterns are passed to the RegExp constructor as ECMAScript string values in which non-BMP characters are UTF-16 - encoded. For example, the single character MUSICAL SYMBOL G CLEF pattern, expressed as a string value, is a String of - length 2 whose elements were the code units 0xD834 and 0xDD1E. So no further translation of the string would be - necessary to process it as a BMP pattern consisting of two pattern characters. However, to process it as a Unicode - pattern the string value must treated as if it was UTF-16 decoded into a List consisting of a single pattern character, the code point - U+1D11E.

- -

An implementation may not actually perform such translations to or from UTF-16, but the semantics of this - specification requires that the result of pattern matching be as if such translations were performed.

-
-
- -
-

21.2.2.1 - Notation

- -

The descriptions below use the following variables:

- -
    -
  • -

    Input is a List consisting of all of - the characters, in order, of the String being matched by the regular expression pattern. Each character is either a - code unit or a code point, depending upon the kind of pattern involved. The notation input[n] means the nth character of input, where n can range between 0 (inclusive) - and InputLength (exclusive).

    -
    • - -
  • -

    InputLength is the number of characters in Input.

    -
    • - -
  • -

    NcapturingParens is the total number of left capturing parentheses (i.e. the total number - of times the Atom :: ( - Disjunction ) production is expanded) in the pattern. A left - capturing parenthesis is any ( pattern character that is matched by the ( terminal of the - Atom :: ( Disjunction ) production.

    -
    • - -
  • -

    IgnoreCase is true if the RegExp object's [[OriginalFlags]] internal slot contains "i" and otherwise is - false.

    -
    • - -
  • -

    Multiline is true if the RegExp object’s [[OriginalFlags]] internal slot contains "m" and otherwise is - false.

    -
    • - -
  • -

    Unicode is true if the RegExp object’s [[OriginalFlags]] internal slot contains "u" and otherwise is - false.

    -
    • -
- -

Furthermore, the descriptions below use the following internal data structures:

- -
    -
  • -

    A CharSet is a mathematical set of characters, either code units or code points depending - up the state of the Unicode flag. “All characters” means either all code unit - values or all code point values also depending upon the state if Unicode.

    -
    • - -
  • -

    A State is an ordered pair (endIndex, - captures) where endIndex is an integer and captures is a List of NcapturingParens values. States are used to represent partial match states in the regular expression matching algorithms. The - endIndex is one plus the index of the last input character matched so far by the pattern, while - captures holds the results of capturing parentheses. The nth element of captures is either a List that represents the value obtained by the nth set of capturing parentheses or undefined if - the nth set of capturing parentheses hasn’t - been reached yet. Due to backtracking, many States may be in use at any time during the - matching process.

    -
    • - -
  • -

    A MatchResult is either a State or the special token failure - that indicates that the match failed.

    -
    • - -
  • -

    A Continuation procedure is an internal closure (i.e. an internal procedure with some - arguments already bound to values) that takes one State argument and returns a MatchResult result. If an internal closure references variables which are bound in the function that - creates the closure, the closure uses the values that these variables had at the time the closure was created. The - Continuation attempts to match the remaining portion (specified by the closure's already-bound - arguments) of the pattern against Input, starting at the intermediate state given by its State argument. If the match succeeds, the Continuation returns the final - State that it reached; if the match fails, the Continuation returns - failure.

    -
    • - -
  • -

    A Matcher procedure is an internal closure that takes two arguments — a State and a Continuation — and returns a MatchResult result. A Matcher attempts to match a middle subpattern - (specified by the closure's already-bound arguments) of the pattern against Input, starting at - the intermediate state given by its State argument. The Continuation - argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to - obtain a new State, the Matcher then calls Continuation on that new State to test if the rest of the pattern can match - as well. If it can, the Matcher returns the State returned by Continuation; if not, the Matcher may try different choices at its choice - points, repeatedly calling Continuation until it either succeeds or all possibilities have - been exhausted.

    -
    • - -
  • -

    An AssertionTester procedure is an internal closure that takes a State argument and returns a Boolean result. The assertion tester tests a specific condition - (specified by the closure's already-bound arguments) against the current place in Input and - returns true if the condition matched or false if not.

    -
    • - -
  • -

    An EscapeValue is either a character or an integer. An EscapeValue - is used to denote the interpretation of a DecimalEscape escape sequence: a character - ch means that the escape sequence is interpreted as the character ch, while an integer - n means that the escape sequence is interpreted as a backreference to the nth set of capturing parentheses.

    -
    • -
-
- -
-

21.2.2.2 - Pattern

- -

The production Pattern :: Disjunction evaluates as follows:

- -
    -
  1. Evaluate Disjunction to obtain a Matcher m.
    2. -
  2. Return an internal closure that takes two arguments, a String str and an integer index, and performs - the following: -
      -
    1. If Unicode is true, then let Input be a List consisting of the sequence of code points of str - interpreted as a UTF-16 encoded Unicode string. Otherwise, let Input be a List consisting of the sequence of code units that are the - elements of str. Input will be used throughout the algorithms in 21.2.2. Each element of Input is considered to be a character.
      2. -
    2. Let listIndex be the index into Input of the character that was obtained from element index - of str.
      3. -
    3. Let InputLength be the number of characters contained in Input. This variable will be used - throughout the algorithms in 21.2.2.
      4. -
    4. Let c be a Continuation that always returns its State argument as a successful MatchResult.
      5. -
    5. Let cap be a List of NcapturingParens - undefined values, indexed 1 through NcapturingParens.
      6. -
    6. Let x be the State (listIndex, cap).
      7. -
    7. Call m(x, c) and return its result.
      8. -
    -
    3. -
- -
-

NOTE A Pattern evaluates ("compiles") to an internal procedure value. RegExp.prototype.exec and other methods can then apply this procedure to a - String and an offset within the String to determine whether the pattern would match starting at exactly that offset - within the String, and, if it does match, what the values of the capturing parentheses would be. The algorithms in 21.2.2 are designed so that compiling a pattern may throw a SyntaxError - exception; on the other hand, once the pattern is successfully compiled, applying its result internal procedure to find - a match in a String cannot throw an exception (except for any host-defined exceptions that can occur anywhere such as - out-of-memory).

-
-
- -
-

21.2.2.3 - Disjunction

- -

The production Disjunction :: Alternative evaluates by evaluating Alternative to obtain a Matcher and returning that Matcher.

- -

The production Disjunction :: Alternative | Disjunction evaluates as - follows:

- -
    -
  1. Evaluate Alternative to obtain a Matcher m1.
    2. -
  2. Evaluate Disjunction to obtain a Matcher m2.
    3. -
  3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following: -
      -
    1. Call m1(x, c) and let r be its result.
      2. -
    2. If r isn't failure, return r.
      3. -
    3. Call m2(x, c) and return its result.
      4. -
    -
    4. -
- -
-

NOTE The | regular expression operator separates two alternatives. The pattern - first tries to match the left Alternative (followed by the sequel of the regular expression); if it fails, it - tries to match the right Disjunction (followed by the sequel of the regular expression). If the left - Alternative, the right Disjunction, and the sequel all have choice points, all choices in the sequel are - tried before moving on to the next choice in the left Alternative. If choices in the left Alternative are - exhausted, the right Disjunction is tried instead of the left Alternative. Any capturing parentheses - inside a portion of the pattern skipped by | produce undefined values instead of Strings. Thus, for - example,

- - 
/a|ab/.exec("abc")
- -

returns the result "a" and not "ab". Moreover,

- - 
/((a)|(ab))((c)|(bc))/.exec("abc")
- -

returns the array

- - 
["abc", "a", "a", undefined, "bc", undefined, "bc"]
- -

and not

- - 
["abc", "ab", undefined, "ab", "c", "c", undefined]
-
-
- -
-

21.2.2.4 - Alternative

- -

The production Alternative :: [empty] evaluates by returning a Matcher that takes two arguments, a State x - and a Continuation c, and returns the result of calling c(x).

- -

The production Alternative :: Alternative Term evaluates as follows:

- -
    -
  1. Evaluate Alternative to obtain a Matcher m1.
    2. -
  2. Evaluate Term to obtain a Matcher m2.
    3. -
  3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following: -
      -
    1. Create a Continuation d that takes a State argument y and returns the result of calling - m2(y, c).
      2. -
    2. Call m1(x, d) and return its result.
      3. -
    -
    4. -
- -
-

NOTE Consecutive Terms try to simultaneously match consecutive portions of - Input. If the left Alternative, the right Term, and the sequel of the regular expression all have - choice points, all choices in the sequel are tried before moving on to the next choice in the right Term, and all - choices in the right Term are tried before moving on to the next choice in the left Alternative.

-
-
- -
-
-

21.2.2.5 - Term

- -

The production Term :: Assertion evaluates by returning an internal Matcher closure that takes two arguments, a State - x and a Continuation c, and performs the following:

- -
    -
  1. Evaluate Assertion to obtain an AssertionTester t.
    2. -
  2. Call t(x) and let r be the resulting Boolean value.
    3. -
  3. If r is false, return failure.
    4. -
  4. Call c(x) and return its result.
    5. -
- -

The production Term :: Atom evaluates as follows:

- -
    -
  1. Return the Matcher that is the result of evaluating Atom.
    2. -
- -

The production Term :: Atom Quantifier evaluates as follows:

- -
    -
  1. Evaluate Atom to obtain a Matcher m.
    2. -
  2. Evaluate Quantifier to obtain the three results: an integer min, an integer (or ∞) max, - and Boolean greedy.
    3. -
  3. If max is finite and less than min, then throw a SyntaxError exception.
    4. -
  4. Let parenIndex be the number of left capturing parentheses in the entire regular expression that occur to - the left of this production expansion's Term. This is the total number of times the Atom :: ( Disjunction ) production is expanded prior to this production's - Term plus the total number of Atom :: - ( Disjunction ) productions enclosing - this Term.
    5. -
  5. Let parenCount be the number of left capturing parentheses in the expansion of this production's - Atom. This is the total number of Atom :: ( Disjunction ) - productions enclosed by this production's Atom.
    6. -
  6. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following: -
      -
    1. Call RepeatMatcher(m, min, max, greedy, x, c, parenIndex, - parenCount) and return its result.
      2. -
    -
    7. -
-
- -
-

21.2.2.5.1 Runtime Semantics: RepeatMatcher Abstract Operation

- -

The abstract operation RepeatMatcher takes eight parameters, a - Matcher m, an integer min, an integer (or ∞) max, a Boolean greedy, a - State x, a Continuation c, an integer parenIndex, and an integer parenCount, - and performs the following:

- -
    -
  1. If max is zero, then call c(x) and return its result.
    2. -
  2. Create an internal Continuation closure d that takes one State argument y and performs the - following: -
      -
    1. If min is zero and y's endIndex is equal to x's endIndex, then return - failure.
      2. -
    2. If min is zero then let min2 be zero; otherwise let min2 be min–1.
      3. -
    3. If max is ∞, then let max2 be ∞; otherwise let max2 be - max–1.
      4. -
    4. Call RepeatMatcher(m, min2, max2, greedy, y, c, parenIndex, - parenCount) and return its result.
      5. -
    -
    3. -
  3. Let cap be a fresh copy of x's captures List.
    4. -
  4. For every integer k that satisfies parenIndex < k and k ≤ - parenIndex+parenCount, set cap[k] to undefined.
    5. -
  5. Let e be x's endIndex.
    6. -
  6. Let xr be the State (e, cap).
    7. -
  7. If min is not zero, then call m(xr, d) and return its result.
    8. -
  8. If greedy is false, then -
      -
    1. Call c(x) and let z be its result.
      2. -
    2. If z is not failure, return z.
      3. -
    3. Call m(xr, d) and return its result.
      4. -
    -
    9. -
  9. Call m(xr, d) and let z be its result.
    10. -
  10. If z is not failure, return z.
    11. -
  11. Call c(x) and return its result.
    12. -
- -
-

NOTE 1 An Atom followed by a Quantifier is repeated the number of times - specified by the Quantifier. A Quantifier can be non-greedy, in which case the Atom pattern is - repeated as few times as possible while still matching the sequel, or it can be greedy, in which case the Atom - pattern is repeated as many times as possible while still matching the sequel. The Atom pattern is repeated - rather than the input character sequence that it matches, so different repetitions of the Atom can match - different input substrings.

-
- -
-

NOTE 2 If the Atom and the sequel of the regular expression all have choice points, - the Atom is first matched as many (or as few, if non-greedy) times as possible. All choices in the sequel are - tried before moving on to the next choice in the last repetition of Atom. All choices in the last - (nth) repetition of Atom are tried before moving on to the next choice in the next-to-last - (n–1)st repetition of Atom; at which point it may turn out that more or fewer repetitions of - Atom are now possible; these are exhausted (again, starting with either as few or as many as possible) before - moving on to the next choice in the (n-1)st repetition of Atom and so on.

- -

Compare

- - 
/a[a-z]{2,4}/.exec("abcdefghi")
- -

which returns "abcde" with

- - 
/a[a-z]{2,4}?/.exec("abcdefghi")
- -

which returns "abc".

- -

Consider also

- - 
/(aa|aabaac|ba|b|c)*/.exec("aabaac")
- -

which, by the choice point ordering above, returns the array

- - 
["aaba", "ba"]
- -

and not any of:

- - 
["aabaac", "aabaac"]
- 
["aabaac", "c"]
- -

The above ordering of choice points can be used to write a regular expression that calculates the greatest common - divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:

- - 
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/,"$1")
- -

which returns the gcd in unary notation "aaaaa".

-
- -
-

NOTE 3 Step 5 of the RepeatMatcher clears Atom's captures each time Atom is - repeated. We can see its behaviour in the regular expression

- - 
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")
- -

which returns the array

- - 
["zaacbbbcac", "z", "ac", "a", undefined, "c"]
- -

and not

- - 
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]
- -

because each iteration of the outermost * clears all captured Strings contained in the quantified - Atom, which in this case includes capture Strings numbered 2, 3, 4, and 5.

-
- -
-

NOTE 4 Step 1 of the RepeatMatcher's d closure states that, once the minimum number - of repetitions has been satisfied, any more expansions of Atom that match the empty character sequence are not - considered for further repetitions. This prevents the regular expression engine from falling into an infinite loop on - patterns such as:

- - 
/(a*)*/.exec("b")
- -

or the slightly more complicated:

- - 
/(a*)b\1+/.exec("baaaac")
- -

which returns the array

- - 
["b", ""]
-
-
-
- -
-
-

21.2.2.6 - Assertion

- -

The production Assertion :: ^ evaluates by returning an internal AssertionTester closure that takes a State argument - x and performs the following:

- -
    -
  1. Let e be x's endIndex.
    2. -
  2. If e is zero, return true.
    3. -
  3. If Multiline is false, return false.
    4. -
  4. If the character Input[e–1] is one of LineTerminator, return true.
    5. -
  5. Return false.
    6. -
- -
-

NOTE Even when the y flag is used with a pattern, ^ always - matches only at the beginning of Input, or (if Multiline is true) at the beginning of a line.

-
- -

The production Assertion :: $ evaluates by returning an internal AssertionTester closure that takes a State argument - x and performs the following:

- -
    -
  1. Let e be x's endIndex.
    2. -
  2. If e is equal to InputLength, return true.
    3. -
  3. If Multiline is false, return false.
    4. -
  4. If the character Input[e] is one of LineTerminator, return true.
    5. -
  5. Return false.
    6. -
- -

The production Assertion :: \ b evaluates by returning an internal AssertionTester closure that takes - a State argument x and performs the following:

- -
    -
  1. Let e be x's endIndex.
    2. -
  2. Call IsWordChar(e–1) and let a be the Boolean result.
    3. -
  3. Call IsWordChar(e) and let b be the Boolean result.
    4. -
  4. If a is true and b is false, return true.
    5. -
  5. If a is false and b is true, return true.
    6. -
  6. Return false.
    7. -
- -

The production Assertion :: \ B evaluates by returning an internal AssertionTester closure that takes - a State argument x and performs the following:

- -
    -
  1. Let e be x's endIndex.
    2. -
  2. Call IsWordChar(e–1) and let a be the Boolean result.
    3. -
  3. Call IsWordChar(e) and let b be the Boolean result.
    4. -
  4. If a is true and b is false, return false.
    5. -
  5. If a is false and b is true, return false.
    6. -
  6. Return true.
    7. -
- -

The production Assertion :: ( ? = Disjunction ) evaluates as follows:

- -
    -
  1. Evaluate Disjunction to obtain a Matcher m.
    2. -
  2. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following steps: -
      -
    1. Let d be a Continuation that always returns its State argument as a successful MatchResult.
      2. -
    2. Call m(x, d) and let r be its result.
      3. -
    3. If r is failure, return failure.
      4. -
    4. Let y be r's State.
      5. -
    5. Let cap be y's captures List.
      6. -
    6. Let xe be x's endIndex.
      7. -
    7. Let z be the State (xe, cap).
      8. -
    8. Call c(z) and return its result.
      9. -
    -
    3. -
- -

The production Assertion :: ( ? ! Disjunction ) evaluates as follows:

- -
    -
  1. Evaluate Disjunction to obtain a Matcher m.
    2. -
  2. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following steps: -
      -
    1. Let d be a Continuation that always returns its State argument as a successful MatchResult.
      2. -
    2. Call m(x, d) and let r be its result.
      3. -
    3. If r isn't failure, return failure.
      4. -
    4. Call c(x) and return its result.
      5. -
    -
    3. -
-
- -
-

21.2.2.6.1 Runtime Semantics: IsWordChar Abstract Operation

- -

The abstract operation IsWordChar takes an integer parameter e and performs the following:

- -
    -
  1. If e is –1 or e is InputLength, return false.
    2. -
  2. Let c be the character Input[e].
    3. -
  3. If c is one of the sixty-three characters below, return true. -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    abcdefghijklmnopqrstuvwxyz
    ABCDEFGHIJKLMNOPQRSTUVWXYZ
    0123456789_
    -
    -
    4. -
  4. Return false.
    5. -
-
-
- -
-

21.2.2.7 - Quantifier

- -

The production Quantifier :: QuantifierPrefix evaluates as follows:

- -
    -
  1. Evaluate QuantifierPrefix to obtain the two results: an integer min and an integer (or ∞) - max.
    2. -
  2. Return the three results min, max, and true.
    3. -
- -

The production Quantifier :: QuantifierPrefix ? evaluates as follows:

- -
    -
  1. Evaluate QuantifierPrefix to obtain the two results: an integer min and an integer (or ∞) - max.
    2. -
  2. Return the three results min, max, and false.
    3. -
- -

The production QuantifierPrefix :: * evaluates as follows:

- -
    -
  1. Return the two results 0 and ∞.
    2. -
- -

The production QuantifierPrefix :: + evaluates as follows:

- -
    -
  1. Return the two results 1 and ∞.
    2. -
- -

The production QuantifierPrefix :: ? evaluates as follows:

- -
    -
  1. Return the two results 0 and 1.
    2. -
- -

The production QuantifierPrefix :: { DecimalDigits } evaluates as follows:

- -
    -
  1. Let i be the MV of DecimalDigits (see 11.8.3).
    2. -
  2. Return the two results i and i.
    3. -
- -

The production QuantifierPrefix :: { DecimalDigits , } - evaluates as follows:

- -
    -
  1. Let i be the MV of DecimalDigits.
    2. -
  2. Return the two results i and ∞.
    3. -
- -

The production QuantifierPrefix :: { DecimalDigits , DecimalDigits - } evaluates as follows:

- -
    -
  1. Let i be the MV of the first DecimalDigits.
    2. -
  2. Let j be the MV of the second DecimalDigits.
    3. -
  3. Return the two results i and j.
    4. -
-
- -
-
-

21.2.2.8 - Atom

- -

The production Atom :: PatternCharacter evaluates as follows:

- -
    -
  1. Let ch be the character matched by PatternCharacter.
    2. -
  2. Let A be a one-element CharSet containing the character ch.
    3. -
  3. Call CharacterSetMatcher(A, false) and return its Matcher result.
    4. -
- -

The production Atom :: . evaluates as follows:

- -
    -
  1. Let A be the set of all characters except LineTerminator.
    2. -
  2. Call CharacterSetMatcher(A, false) and return its Matcher result.
    3. -
- -

The production Atom :: \ - AtomEscape evaluates as follows:

- -
    -
  1. Return the Matcher that is the result of evaluating AtomEscape.
    2. -
- -

The production Atom :: CharacterClass evaluates as follows:

- -
    -
  1. Evaluate CharacterClass to obtain a CharSet A and a Boolean invert.
    2. -
  2. Call CharacterSetMatcher(A, invert) and return its Matcher result.
    3. -
- -

The production Atom :: ( - Disjunction ) evaluates as follows:

- -
    -
  1. Evaluate Disjunction to obtain a Matcher m.
    2. -
  2. Let parenIndex be the number of left capturing parentheses in the entire regular expression that occur to - the left of this production expansion's initial left parenthesis. This is the total number of times the Atom :: ( Disjunction ) production is expanded prior to this production's - Atom plus the total number of Atom :: - ( Disjunction ) productions enclosing - this Atom.
    3. -
  3. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following steps: -
      -
    1. Create an internal Continuation closure d that takes one State argument y and performs the - following steps: -
        -
      1. Let cap be a fresh copy of y's captures List.
        2. -
      2. Let xe be x's endIndex.
        3. -
      3. Let ye be y's endIndex.
        4. -
      4. Let s be a fresh List whose characters are - the characters of Input at positions xe (inclusive) through ye (exclusive).
        5. -
      5. Set cap[parenIndex+1] to s.
        6. -
      6. Let z be the State (ye, cap).
        7. -
      7. Call c(z) and return its result.
        8. -
      -
      2. -
    2. Call m(x, d) and return its result.
      3. -
    -
    4. -
- -

The production Atom :: ( - ? : Disjunction ) - evaluates as follows:

- -
    -
  1. Return the Matcher that is the result of evaluating Disjunction.
    2. -
-
- -
-

21.2.2.8.1 Runtime Semantics: CharacterSetMatcher Abstract Operation

- -

The abstract operation CharacterSetMatcher takes two arguments, a CharSet A and a Boolean flag - invert, and performs the following:

- -
    -
  1. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following steps: -
      -
    1. Let e be x's endIndex.
      2. -
    2. If e is InputLength, return failure.
      3. -
    3. Let ch be the character Input[e].
      4. -
    4. Let cc be the result of Canonicalize(ch).
      5. -
    5. If invert is false, then -
        -
      1. If there does not exist a member a of set A such that Canonicalize(a) is cc, - return failure.
        2. -
      -
      6. -
    6. Else invert is true, -
        -
      1. If there exists a member a of set A such that Canonicalize(a) is cc, return - failure.
        2. -
      -
      7. -
    7. Let cap be x's captures List.
      8. -
    8. Let y be the State (e+1, cap).
      9. -
    9. Call c(y) and return its result.
      10. -
    -
    2. -
-
- -
-

21.2.2.8.2 Runtime Semantics: Canonicalize Abstract Operation

- -

The abstract operation Canonicalize takes a character parameter ch and performs the following steps:

- -
    -
  1. If IgnoreCase is false, return ch.
    2. -
  2. If Unicode is true, -
      -
    1. If the file CaseFolding.txt of the Unicode Character Database provides a simple or common case folding mapping - for ch, then return the result of applying that mapping to ch.
      2. -
    2. Else, return ch.
      3. -
    -
    3. -
  3. Else, -
      -
    1. Assert: ch is a UTF-16 code unit.
      2. -
    2. Let s be the ECMAScript String value consisting of the single code unit ch.
      3. -
    3. Let u be the same result produced as if by performing the algorithm for String.prototype.toUpperCase using s as the - this value.
      4. -
    4. ReturnIfAbrupt(u).
      5. -
    5. Assert: u is a String value.
      6. -
    6. If u does not consist of a single code unit, then return ch.
      7. -
    7. Let cu be u’s single code unit element.
      8. -
    8. If ch's code unit value ≥ 128 and cu's code unit value < 128, then return ch.
      9. -
    9. Return cu.
      10. -
    -
    4. -
- -
-

NOTE 1 Parentheses of the form ( Disjunction ) serve both - to group the components of the Disjunction pattern together and to save the result of the match. The result can - be used either in a backreference (\ followed by a nonzero decimal number), referenced in a replace - String, or returned as part of an array from the regular expression matching internal procedure. To inhibit the - capturing behaviour of parentheses, use the form (?: Disjunction ) instead.

-
- -
-

NOTE 2 The form (?= Disjunction ) specifies a zero-width - positive lookahead. In order for it to succeed, the pattern inside Disjunction must match at the current - position, but the current position is not advanced before matching the sequel. If Disjunction can match at the - current position in several ways, only the first one is tried. Unlike other regular expression operators, there is no - backtracking into a (?= form (this unusual behaviour is inherited from Perl). This only matters when the - Disjunction contains capturing parentheses and the sequel of the pattern contains backreferences to those - captures.

- -

For example,

- - 
/(?=(a+))/.exec("baaabac")
- -

matches the empty String immediately after the first b and therefore returns the array:

- - 
["", "aaa"]
- -

To illustrate the lack of backtracking into the lookahead, consider:

- - 
/(?=(a+))a*b\1/.exec("baaabac")
- -

This expression returns

- - 
["aba", "a"]
- -

and not:

- - 
["aaaba", "a"]
-
- -
-

NOTE 3 The form (?! Disjunction ) specifies a zero-width - negative lookahead. In order for it to succeed, the pattern inside Disjunction must fail to match at the - current position. The current position is not advanced before matching the sequel. Disjunction can contain - capturing parentheses, but backreferences to them only make sense from within Disjunction itself. - Backreferences to these capturing parentheses from elsewhere in the pattern always return undefined because the - negative lookahead must fail for the pattern to succeed. For example,

- - 
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")
- -

looks for an a not immediately followed by some positive number n of a's, a - b, another n a's (specified by the first \2) and a c. The second - \2 is outside the negative lookahead, so it matches against undefined and therefore always - succeeds. The whole expression returns the array:

- - 
["baaabaac", "ba", undefined, "abaac"]
-
- -
-

NOTE 4 In case-insignificant matches when Unicode is true, all characters are - implicitly case-folded using the simple mapping provided by the Unicode standard immediately before they are compared. - The simple mapping always maps to a single code point, so it does not map, for example, "ß" (U+00DF - to "SS". It may however map a code point outside the Basic Latin range to a character within, for - example, “ſ” (U+017F) to “s”. Such - characters are not mapped if Unicode is false. This prevents Unicode code points such as U+0131 and - U+017F from matching regular expressions such as /[a‑z]/i, but they will match - /[a‑z]/ui.

-
-
-
- -
-

21.2.2.9 - AtomEscape

- -

The production AtomEscape :: DecimalEscape evaluates as follows:

- -
    -
  1. Evaluate DecimalEscape to obtain an EscapeValue E.
    2. -
  2. If E is a character, then -
      -
    1. Let ch be E's character.
      2. -
    2. Let A be a one-element CharSet containing the character ch.
      3. -
    3. Call CharacterSetMatcher(A, false) and return its Matcher result.
      4. -
    -
    3. -
  3. Assert: E must be an integer.
    4. -
  4. Let n be that integer.
    5. -
  5. If n=0 or n>NcapturingParens then throw a SyntaxError exception.
    6. -
  6. Return an internal Matcher closure that takes two arguments, a State x and a Continuation c, and - performs the following steps: -
      -
    1. Let cap be x's captures List.
      2. -
    2. Let s be cap[n].
      3. -
    3. If s is undefined, then call c(x) and return its result.
      4. -
    4. Let e be x's endIndex.
      5. -
    5. Let len be s's length.
      6. -
    6. Let f be e+len.
      7. -
    7. If f>InputLength, return failure.
      8. -
    8. If there exists an integer i between 0 (inclusive) and len (exclusive) such that - Canonicalize(s[i]) is not the same character value as Canonicalize(Input - [e+i]), then return failure.
      9. -
    9. Let y be the State (f, cap).
      10. -
    10. Call c(y) and return its result.
      11. -
    -
    7. -
- -

The production AtomEscape :: CharacterEscape evaluates as follows:

- -
    -
  1. Evaluate CharacterEscape to obtain a character ch.
    2. -
  2. Let A be a one-element CharSet containing the character ch.
    3. -
  3. Call CharacterSetMatcher(A, false) and return its Matcher result.
    4. -
- -

The production AtomEscape :: CharacterClassEscape evaluates as follows:

- -
    -
  1. Evaluate CharacterClassEscape to obtain a CharSet A.
    2. -
  2. Call CharacterSetMatcher(A, false) and return its Matcher result.
    3. -
- -
-

NOTE An escape sequence of the form \ followed by a nonzero decimal number - n matches the result of the nth set of capturing parentheses (see - 21.2.2.11). It is an error if the regular expression has fewer than n capturing parentheses. If the regular - expression has n or more capturing parentheses but the nth one is undefined because it has not - captured anything, then the backreference always succeeds.

-
-
- -
-

21.2.2.10 CharacterEscape

- -

The production CharacterEscape :: ControlEscape evaluates by returning the character according to Table - 42.

- -
-
Table 42 — ControlEscape Character Values
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
ControlEscapeCharacter ValueCode PointNameSymbol
t9U+0009horizontal tab<HT>
n10U+000Aline feed (new line)<LF>
v11U+000Bvertical tab<VT>
f12U+000Cform feed<FF>
r13U+000Dcarriage return<CR>
-
- -

The production CharacterEscape :: c ControlLetter evaluates as follows:

- -
    -
  1. Let ch be the character matched by ControlLetter.
    2. -
  2. Let i be ch's character value.
    3. -
  3. Let j be the remainder of dividing i by 32.
    4. -
  4. Return the character whose character value is j.
    5. -
- -

The production CharacterEscape :: HexEscapeSequence evaluates as follows:

- -
    -
  1. Return the character whose code is the CV of HexEscapeSequence.
    2. -
- -

The production CharacterEscape :: RegExpUnicodeEscapeSequence evaluates as follows:

- -
    -
  1. Return the result of evaluating RegExpUnicodeEscapeSequence.
    2. -
- -

The production CharacterEscape :: IdentityEscape evaluates as follows:

- -
    -
  1. Return the character matched by IdentityEscape.
    2. -
- -

The production RegExpUnicodeEscapeSequence :: u LeadSurrogate \u TrailSurrogate evaluates as follows:

- -
    -
  1. Let lead be the result of evaluating LeadSurrogate.
    2. -
  2. Let trail be the result of evaluating TrailSurrogate.
    3. -
  3. Let cp be UTF16Decode(lead, trail).
    4. -
  4. Return the character whose character value is cp.
    5. -
- -

The production RegExpUnicodeEscapeSequence :: u Hex4Digits evaluates as follows:

- -
    -
  1. Return the character whose code is the CV of Hex4Digits.
    2. -
- -

The production RegExpUnicodeEscapeSequence :: u{ HexDigits } evaluates as follows:

- -
    -
  1. Return the character whose code is the MV of HexDigits.
    2. -
- -

The production LeadSurrogate :: Hex4Digits evaluates as follows:

- -
    -
  1. Return the character whose code is the CV of Hex4Digits.
    2. -
- -

The production TrailSurrogate :: Hex4Digits evaluates as follows:

- -
    -
  1. Return the character whose code is the CV of Hex4Digits.
    2. -
-
- -
-

21.2.2.11 - DecimalEscape

- -

The production DecimalEscape :: DecimalIntegerLiteral evaluates as follows:

- -
    -
  1. Let i be the MV of DecimalIntegerLiteral.
    2. -
  2. If i is zero, return the EscapeValue consisting of the character U+0000 (NULL).
    3. -
  3. Return the EscapeValue consisting of the integer i.
    4. -
- -

The definition of “the MV of DecimalIntegerLiteral” is in 11.8.3.

- -
-

NOTE If \ is followed by a decimal number n whose first digit is not - 0, then the escape sequence is considered to be a backreference. It is an error if n is greater than - the total number of left capturing parentheses in the entire regular expression. \0 represents the - <NUL> character and cannot be followed by a decimal digit.

-
-
- -
-

21.2.2.12 CharacterClassEscape

- -

The production CharacterClassEscape :: d evaluates by returning the ten-element set of characters containing the characters - 0 through 9 inclusive.

- -

The production CharacterClassEscape :: D evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: d - .

- -

The production CharacterClassEscape :: s evaluates by returning the set of characters containing the characters that are on the - right-hand side of the WhiteSpace (11.2) or LineTerminator (11.3) productions.

- -

The production CharacterClassEscape :: S evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: s - .

- -

The production CharacterClassEscape :: w evaluates by returning the set of characters containing the sixty-three characters:

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
abcdefghijklmnopqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ
0123456789_
-
- -

The production CharacterClassEscape :: W evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: w - .

-
- -
-

21.2.2.13 CharacterClass

- -

The production CharacterClass :: [ ClassRanges ] evaluates by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the Boolean false.

- -

The production CharacterClass :: [ ^ ClassRanges ] evaluates - by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the Boolean - true.

-
- -
-

21.2.2.14 - ClassRanges

- -

The production ClassRanges :: [empty] evaluates by returning the empty CharSet.

- -

The production ClassRanges :: NonemptyClassRanges evaluates by evaluating NonemptyClassRanges to obtain - a CharSet and returning that CharSet.

-
- -
-
-

21.2.2.15 NonemptyClassRanges

- -

The production NonemptyClassRanges :: ClassAtom evaluates as follows:

- -
    -
  1. Return the CharSet that is the result of evaluating ClassAtom.
    2. -
- -

The production NonemptyClassRanges :: ClassAtom NonemptyClassRangesNoDash evaluates as follows:

- -
    -
  1. Evaluate ClassAtom to obtain a CharSet A.
    2. -
  2. Evaluate NonemptyClassRangesNoDash to obtain a CharSet B.
    3. -
  3. Return the union of CharSets A and B.
    4. -
- -

The production NonemptyClassRanges :: ClassAtom - ClassAtom ClassRanges evaluates as follows:

- -
    -
  1. Evaluate the first ClassAtom to obtain a CharSet A.
    2. -
  2. Evaluate the second ClassAtom to obtain a CharSet B.
    3. -
  3. Evaluate ClassRanges to obtain a CharSet C.
    4. -
  4. Call CharacterRange(A, B) and let D be the resulting CharSet.
    5. -
  5. Return the union of CharSets D and C.
    6. -
-
- -
-

21.2.2.15.1 Runtime Semantics: CharacterRange Abstract Operation

- -

The abstract operation CharacterRange takes two CharSet parameters A and B and performs the - following:

- -
    -
  1. If A does not contain exactly one character or B does not contain exactly one character then throw a - SyntaxError exception.
    2. -
  2. Let a be the one character in CharSet A.
    3. -
  3. Let b be the one character in CharSet B.
    4. -
  4. Let i be the character value of character a.
    5. -
  5. Let j be the character value of character b.
    6. -
  6. If i > j then throw a SyntaxError exception.
    7. -
  7. Return the set containing all characters numbered i through j, inclusive.
    8. -
-
-
- -
-

21.2.2.16 NonemptyClassRangesNoDash

- -

The production NonemptyClassRangesNoDash :: ClassAtom evaluates as follows:

- -
    -
  1. Return the CharSet that is the result of evaluating ClassAtom.
    2. -
- -

The production NonemptyClassRangesNoDash :: ClassAtomNoDash NonemptyClassRangesNoDash evaluates as follows:

- -
    -
  1. Evaluate ClassAtomNoDash to obtain a CharSet A.
    2. -
  2. Evaluate NonemptyClassRangesNoDash to obtain a CharSet B.
    3. -
  3. Return the union of CharSets A and B.
    4. -
- -

The production NonemptyClassRangesNoDash :: ClassAtomNoDash - ClassAtom ClassRanges evaluates as follows:

- -
    -
  1. Evaluate ClassAtomNoDash to obtain a CharSet A.
    2. -
  2. Evaluate ClassAtom to obtain a CharSet B.
    3. -
  3. Evaluate ClassRanges to obtain a CharSet C.
    4. -
  4. Call CharacterRange(A, B) and let D be the resulting CharSet.
    5. -
  5. Return the union of CharSets D and C.
    6. -
- -
-

NOTE 1 ClassRanges can expand into single ClassAtoms and/or ranges of two - ClassAtoms separated by dashes. In the latter case the ClassRanges includes all characters between the - first ClassAtom and the second ClassAtom, inclusive; an error occurs if either ClassAtom does not - represent a single character (for example, if one is \w) or if the first ClassAtom's character value - is greater than the second ClassAtom's character value.

-
- -
-

NOTE 2 Even if the pattern ignores case, the case of the two ends of a range is significant - in determining which characters belong to the range. Thus, for example, the pattern /[E-F]/i matches only - the letters E, F, e, and f, while the pattern /[E-f]/i - matches all upper and lower-case letters in the Unicode Basic Latin block as well as the symbols [, - \, ], ^, _, and `.

-
- -
-

NOTE 3 A - character can be treated literally or it can denote a range. It is - treated literally if it is the first or last character of ClassRanges, the beginning or end - limit of a range specification, or immediately follows a range specification.

-
-
- -
-

21.2.2.17 - ClassAtom

- -

The production ClassAtom :: - evaluates by returning the CharSet containing the one character -.

- -

The production ClassAtom :: ClassAtomNoDash evaluates by evaluating ClassAtomNoDash to obtain a - CharSet and returning that CharSet.

-
- -
-

21.2.2.18 ClassAtomNoDash

- -

The production ClassAtomNoDash :: SourceCharacter but not one of \ or ] or - - evaluates as follows:

- -
    -
  1. Return the CharSet containing the character matched by SourceCharacter.
    2. -
- -

The production ClassAtomNoDash :: \ ClassEscape evaluates as follows:

- -
    -
  1. Return the CharSet that is the result of evaluating ClassEscape.
    2. -
-
- -
-

21.2.2.19 - ClassEscape

- -

The production ClassEscape :: DecimalEscape evaluates as follows:

- -
    -
  1. Evaluate DecimalEscape to obtain an EscapeValue E.
    2. -
  2. If E is not a character then throw a SyntaxError exception.
    3. -
  3. Let ch be E's character.
    4. -
  4. Return the one-element CharSet containing the character ch.
    5. -
- -

The production ClassEscape :: b evaluates as follows:

- -
    -
  1. Return the CharSet containing the single character <BS> U+0008 (BACKSPACE).
    2. -
- -

The production ClassEscape :: CharacterEscape evaluates as follows:

- -
    -
  1. Return the CharSet containing the single character that is the result of evaluating CharacterEscape.
    2. -
- -

The production ClassEscape :: CharacterClassEscape evaluates as follows:

- -
    -
  1. Return the CharSet that is the result of evaluating CharacterClassEscape.
    2. -
- -
-

NOTE A ClassAtom can use any of the escape sequences that are allowed in the rest of - the regular expression except for \b, \B, and backreferences. Inside a CharacterClass, - \b means the backspace character, while \B and backreferences raise errors. Using a - backreference inside a ClassAtom causes an error.

-
-
-
- -
-
-

21.2.3 - The RegExp Constructor

- -

The RegExp constructor is the %RegExp% intrinsic object and the initial value of the RegExp property of - the global object. When RegExp is called as a function rather than as a constructor, it creates and - initializes a new RegExp object. Thus the function call RegExp(…) is equivalent to the - object creation expression new RegExp(…) with the same arguments. However, if the - this value passed in the call is an Object with a [[RegExpMatcher]] internal slot whose value is undefined, it initializes the this value using the argument values. This permits - RegExp to be used both as factory method and to perform constructor instance initialization.

- -

The RegExp constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - RegExp behaviour must include a super call to the RegExp constructor to initialize - subclass instances.

-
- -
-

21.2.3.1 RegExp ( pattern, flags )

- -

The following steps are taken:

- -
    -
  1. Let func be this RegExp function object.
    2. -
  2. Let O be the this value.
    3. -
  3. If Type(O) is not Object or Type(O) is Object and O does not have a - [[RegExpMatcher]] internal slot or Type(O) is Object and O has a [[RegExpMatcher]] internal slot and the value of [[RegExpMatcher]] is not - undefined, then -
      -
    1. If Type(pattern) is Object and O has a - [[RegExpMatcher]] internal slot and flags - is undefined, then -
        -
      1. Return pattern;
        2. -
      -
      2. -
    2. Let O be the result of calling the abstract operation RegExpAlloc with - argument func.
      3. -
    3. ReturnIfAbrupt(O).
      4. -
    -
    4. -
  4. If Type(pattern) is Object and pattern has a - [[RegExpMatcher]] internal slot, then -
      -
    1. If the value of pattern’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
      2. -
    2. If flags is not undefined, then throw a TypeError exception.
      3. -
    3. Let P be the value of pattern’s [[OriginalSource]] internal slot.
      4. -
    4. Let F be the value of pattern’s [[OriginalFlags]] internal slot.
      5. -
    -
    5. -
  5. Else, -
      -
    1. Let P be pattern.
      2. -
    2. Let F be flags.
      3. -
    -
    6. -
  6. Return the result of the abstract operation RegExpInitialize with arguments - O, P, and F.
    7. -
- -
-

NOTE If pattern is supplied using a StringLiteral, the usual escape sequence - substitutions are performed before the String is processed by RegExp. If pattern must contain an escape sequence to be - recognized by RegExp, any backslash \ characters must be escaped within the StringLiteral to prevent - them being removed when the contents of the StringLiteral are formed.

-
-
- -
-

21.2.3.2 new RegExp( ...argumentsList )

- -

When RegExp is called as part of a new expression with argument list argumentsList it performs - the following steps:

- -
    -
  1. Let F be the RegExp function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If RegExp is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
- -
-
-

21.2.3.3 Abstract Operations for the RegExp Constructor

-
- -
-

21.2.3.3.1 Runtime Semantics: RegExpAlloc Abstract Operation

- -

When the abstract operation RegExpAlloc with argument constructor is called, the following steps are - taken:

- -
    -
  1. Let obj be the result of calling OrdinaryCreateFromConstructor(constructor, - "%RegExpPrototype%", ( [[RegExpMatcher]], [[OriginalSource]], [[OriginalFlags]])).
    2. -
  2. Let status be the result of DefinePropertyOrThrow(obj, - "lastIndex", PropertyDescriptor {[[Writable]]: true, [[Enumberable]]: false, - [[Configurable]]: false}).
    3. -
  3. ReturnIfAbrupt(status).
    4. -
  4. Return obj.
    5. -
- -
-

NOTE [[RegExpMatcher]] is initially assigned the value undefined as a flag to - indicate that the instance has not yet been initialized by the RegExp constructor. This flag value is never - directly exposed to ECMAScript code; hence implementations may choose to encode the flag in some other manner.

-
-
- -
-

21.2.3.3.2 Runtime Semantics: RegExpInitialize Abstract Operation

- -

When the abstract operation RegExpInitialize with arguments obj, pattern, and flags is called, the following steps are taken:

- -
    -
  1. If pattern is undefined, then let P be the empty String.
    2. -
  2. Else, let P be ToString(pattern).
    3. -
  3. ReturnIfAbrupt(P).
    4. -
  4. If flags is undefined, then let F be the empty String.
    5. -
  5. Else, let F be ToString(flags).
    6. -
  6. ReturnIfAbrupt(F).
    7. -
  7. If F contains any character other than "g", "i", "m", - "u", or "y" or if it contains the same character more than once, then throw a - SyntaxError exception.
    8. -
  8. If F contains "u" then let BMP be false, else let BMP be - true.
    9. -
  9. If BMP is true, then -
      -
    1. Parse P interpreted as UTF-16 encoded Unicode code points using the grammars in 21.2.1. The goal symbol for the parse is Pattern.Throw a SyntaxError - exception if P did not conform to the grammar or if any characters of P where not matched by the - parse.
      2. -
    2. Let patternCharacters be a List whose elements - are the code unit elements of P.
      3. -
    -
    10. -
  10. Else -
      -
    1. Parse P interpreted as UTF-16 encoded Unicode code points using the grammars in 21.2.1. The goal symbol for the parse is Pattern[U]. Throw a - SyntaxError exception if P did not conform to the grammar or if any characters of P where - not matched by the parse.
      2. -
    2. Let patternCharacters be a List whose elements - are the code points of P interpreted as sequence of UTF-16 encoded Unicode code points.
      3. -
    -
    11. -
  11. Set the value of obj’s [[OriginalSource]] internal slot to P.
    12. -
  12. Set the value of obj’s [[OriginalFlags]] internal slot to F.
    13. -
  13. Set obj’s [[RegExpMatcher]] internal - slot to the internal procedure that evaluates the above parse of P by applying the semantics provided - in 21.2.2 using patternCharacters as the pattern’s List of SourceCharacter values and F as the flag - parameters.
    14. -
  14. Let putStatus be the result of Put(obj, "lastIndex", - 0, true).
    15. -
  15. ReturnIfAbrupt(putStatus).
    16. -
  16. Return obj.
    17. -
-
- -
-

21.2.3.3.3 Runtime Semantics: RegExpCreate Abstract Operation

- -

When the abstract operation RegExpCreate with arguments P and F is called, the following steps - are taken:

- -
    -
  1. Let obj be the result of calling the abstract operation RegExpAlloc with - argument %RegExp%.
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of the abstract operation RegExpInitialize with arguments - obj, P, and F .
    4. -
-
- -
-

21.2.3.3.4 Runtime Semantics: EscapeRegExpPattern Abstract Operation

- -

When the abstract operation EscapeRegExpPattern with arguments P and F is called, the following - occurs:

- -

Let S be a String in the form of a Pattern (Pattern[U] if F contains "u") equivalent to P - interpreted as UTF-16 encoded Unicode code points, in which certain code points are escaped as described below. - S may or may not be identical to P; however, the internal procedure that would result from - evaluating S as a Pattern (Pattern[U] if - F contains "u") must behave identically to the internal procedure given by the constructed - object's [[RegExpMatcher]] internal slot. Separate calls - to this abstract operation using the same values for P and F must produce identical results.

- -

The characters / or any LineTerminator occurring in the pattern shall be escaped - in S as necessary to ensure that the String value formed by concatenating the Strings "/", - S, "/", and F can be parsed (in an appropriate lexical context) as a RegularExpressionLiteral that behaves identically to the constructed regular expression. For example, - if P is "/", then S could be "\/" or "\u002F", among other - possibilities, but not "/", because /// followed by F would be parsed as a SingleLineComment rather than a RegularExpressionLiteral. If P is - the empty String, this specification can be met by letting S be "(?:)".

- -

Return S.

-
-
-
- -
-
-

21.2.4 Properties of the RegExp Constructor

- -

The value of the [[Prototype]] internal slot of the - RegExp constructor is the standard built-in Function prototype object (19.2.3).

- -

Besides the length property (whose value is 2), the RegExp constructor has the following - properties:

-
- -
-

21.2.4.1 RegExp.prototype

- -

The initial value of RegExp.prototype is the RegExp prototype object (21.2.5).

- -

This property shall have the attributes { [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: false }.

-
- -
-

21.2.4.2 - RegExp[ @@create ] ( )

- -

The @@create method of an object F performs the following:

- -
    -
  1. Return the result of calling the abstract operation RegExpAlloc with argument - F.
    2. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-
-

21.2.5 Properties of the RegExp Prototype Object

- -

The RegExp prototype object is an ordinary object. It is not a RegExp instance and does not have a [[RegExpMatcher]] internal slot or any of the other internal slots of RegExp - instance objects.

- -

The value of the [[Prototype]] internal slot of the - RegExp prototype object is the standard built-in Object prototype object (19.1.3).

- -

The RegExp prototype object does not have a valueOf property of its own; however, it inherits the - valueOf property from the Object prototype object.

-
- -
-

21.2.5.1 RegExp.prototype.constructor

- -

The initial value of RegExp.prototype.constructor is the standard built-in RegExp - constructor.

-
- -
-
-

21.2.5.2 RegExp.prototype.exec ( string )

- -

Performs a regular expression match of string against the regular expression and returns an Array object - containing the results of the match, or null if string did not match.

- -

The String ToString(string) is - searched for an occurrence of the regular expression pattern as follows:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have a [[RegExpMatcher]] internal - slot, then throw a TypeError exception.
    4. -
  4. If the value of R’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
    5. -
  5. Let S be ToString(string)
    6. -
  6. ReturnIfAbrupt(S).
    7. -
  7. Return RegExpBuiltinExec(R, S).
    8. -
-
- -
-

21.2.5.2.1 Runtime Semantics: RegExpExec ( R, S ) Abstract Operation

- -

The abstract operation RegExpExec with arguments R and S performs the following steps:

- -
    -
  1. Assert: Type(R) is Object.
    2. -
  2. Assert: Type(S) is String.
    3. -
  3. Let exec be Get(R, "exec").
    4. -
  4. ReturnIfAbrupt(exec).
    5. -
  5. If IsCallable(exec) is true, then -
      -
    1. Let result be the result of calling the [[Call]] internal method of exec with arguments - R, and (S).
      2. -
    2. ReturnIfAbrupt(result).
      3. -
    3. If Type(result) is neither Object or Null, then - throw a TypeError exception.
      4. -
    4. Return(result).
      5. -
    -
    6. -
  6. If R does not have a [[RegExpMatcher]] internal - slot, then throw a TypeError exception.
    7. -
  7. If the value of R’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
    8. -
  8. Return RegExpBuiltinExec(R, S).
    9. -
- -
-

NOTE If a callable exec property is not found this algorithm falls back to - attempting to use the built-in RegExp matching algoritm. This provides compatable behaviour for code written for prior - editions where most built-in algorithms that use regular expressions did not perform a dynamic property lookup of - exec.

-
-
- -
-

21.2.5.2.2 Runtime Semantics: RegExpBuiltinExec ( R, S ) Abstract - Operation

- -

The abstract operation RegExpBuiltinExec with arguments R and S performs the following - steps:

- -
    -
  1. Assert: R is an initialized RegExp instance.
    2. -
  2. Assert: Type(S) is String.
    3. -
  3. Let length be the number of code units in S.
    4. -
  4. Let lastIndex be Get(R,"lastIndex").
    5. -
  5. Let i be ToInteger(lastIndex).
    6. -
  6. ReturnIfAbrupt(i).
    7. -
  7. Let global be ToBoolean(Get(R, - "global")).
    8. -
  8. ReturnIfAbrupt(global).
    9. -
  9. Let sticky be ToBoolean(Get(R, - "sticky")).
    10. -
  10. ReturnIfAbrupt(sticky).
    11. -
  11. If global is false and sticky is false, then let i = 0.
    12. -
  12. Let matcher be the value of R’s [[RegExpMatcher]] internal slot.
    13. -
  13. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    14. -
  14. If flags contains "u" then let fullUnicode be true, else let fullUnicode - be false.
    15. -
  15. Let matchSucceeded be false.
    16. -
  16. Repeat, while matchSucceeded is false -
      -
    1. If i < 0 or i > length, then -
        -
      1. Let putStatus be Put(R, "lastIndex", - 0, true).
        2. -
      2. ReturnIfAbrupt(putStatus).
        3. -
      3. Return null.
        4. -
      -
      2. -
    2. Let r be the result of calling matcher with arguments S and i.
      3. -
    3. If r is failure, then -
        -
      1. If sticky is true, then -
          -
        1. Let putStatus be Put(R, - "lastIndex", 0, true).
          2. -
        2. ReturnIfAbrupt(putStatus).
          3. -
        3. Return null.
          4. -
        -
        2. -
      2. Let i = i+1.
        3. -
      -
      4. -
    4. else -
        -
      1. Assert: r is a State.
        2. -
      2. Set matchSucceeded to true.
        3. -
      -
      5. -
    -
    17. -
  17. Let e be r's endIndex value.
    18. -
  18. If fullUnicode is true, then -
      -
    1. e is an index into the Input character list, derived from S, matched by matcher. - Let eUTF be the smallest index into S that corresponds to the character at element e of - Input. If e isgreater than the length of Input, then eUTF is 1 + the number of - code units in S.
      2. -
    2. Let e be eUTF.
      3. -
    -
    19. -
  19. If global is true or sticky is true, -
      -
    1. Let putStatus be the result of Put(R, - "lastIndex", e, true).
      2. -
    2. ReturnIfAbrupt(putStatus).
      3. -
    -
    20. -
  20. Let n be the length of r's captures List. (This is the same value as 21.2.2.1's NcapturingParens.)
    21. -
  21. Let A be the result of the abstract operation ArrayCreate(n + - 1).
    22. -
  22. Assert: The value of A’s "length" - property is n + 1.
    23. -
  23. Let matchIndex be i.
    24. -
  24. Assert: The following CreateDataProperty calls will not result in an abrupt completion.
    25. -
  25. Perform CreateDataProperty(A, "index", - matchIndex).
    26. -
  26. Perform CreateDataProperty(A, "input", - S).
    27. -
  27. Let matchedSubstr be the matched substring (i.e. the portion of S between offset i inclusive - and offset e exclusive).
    28. -
  28. Perform CreateDataProperty(A, "0", - matchedSubstr).
    29. -
  29. For each integer i such that i > 0 and i ≤ n -
      -
    1. Let captureI be ith element of r's captures List.
      2. -
    2. If fullUnicode is true, -
        -
      1. Assert: captureI is a List of code points.
        2. -
      2. Let captureString be a string whose elements are the UTF-16Encoding (10.1.1) of the code points of capture.
        3. -
      -
      3. -
    3. Else, fullUnicode is false, -
        -
      1. Assert: captureI is a List of code units.
        2. -
      2. Let captureString be a string whose elements are the code units of captureI.
        3. -
      -
      4. -
    4. Perform CreateDataProperty(A, ToString(i) , captureString).
      5. -
    -
    30. -
  30. Return A.
    31. -
-
-
- -
-

21.2.5.3 get RegExp.prototype.global

- -

RegExp.prototype.global is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    4. -
  4. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    5. -
  5. If flags is undefined, then throw a TypeError exception.
    6. -
  6. If flags contains the character "g", then return true.
    7. -
  7. Return false.
    8. -
-
- -
-

21.2.5.4 get RegExp.prototype.ignoreCase

- -

RegExp.prototype.ignoreCase is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    4. -
  4. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    5. -
  5. If flags is undefined, then throw a TypeError exception.
    6. -
  6. If flags contains the character "i", then return true.
    7. -
  7. Return false.
    8. -
-
- -
-

21.2.5.5 RegExp.prototype.match ( string )

- -

When the match method is called with argument string, the following steps are taken:

- -
    -
  1. Let rx be the this value.
    2. -
  2. If Type(rx) is not Object, then throw a TypeError - exception.
    3. -
  3. Let S be ToString(string)
    4. -
  4. ReturnIfAbrupt(S).
    5. -
  5. Let global be ToBoolean(Get(rx, - "global")).
    6. -
  6. ReturnIfAbrupt(global).
    7. -
  7. If global is not true, then -
      -
    1. Return the result of RegExpExec(rx, S).
      2. -
    -
    8. -
  8. Else global is true, -
      -
    1. Let putStatus be Put(rx, "lastIndex", 0, - true).
      2. -
    2. ReturnIfAbrupt(putStatus).
      3. -
    3. Let A be ArrayCreate(0).
      4. -
    4. Let previousLastIndex be 0.
      5. -
    5. Let n be 0.
      6. -
    6. Repeat, -
        -
      1. Let result be RegExpExec(rx, S).
        2. -
      2. ReturnIfAbrupt(result).
        3. -
      3. If result is null, then -
          -
        1. If n=0, then return null.
          2. -
        2. Else, return A.
          3. -
        -
        4. -
      4. Else result is not null, -
          -
        1. Let thisIndex be ToInteger(Get(rx, - "lastIndex")).
          2. -
        2. ReturnIfAbrupt(thisIndex).
          3. -
        3. If thisIndex = previousLastIndex then -
            -
          1. Let putStatus be Put(rx, "lastIndex", - thisIndex+1, true).
            2. -
          2. ReturnIfAbrupt(putStatus).
            3. -
          3. Set previousLastIndex to thisIndex+1.
            4. -
          -
          4. -
        4. Else, -
            -
          1. Set previousLastIndex to thisIndex.
            2. -
          -
          5. -
        5. Let matchStr be Get(result, "0").
          6. -
        6. Let defineStatus be CreateDataPropertyOrThrow(A, ToString(n), matchStr).
          7. -
        7. ReturnIfAbrupt(defineStatus).
          8. -
        8. Increment n.
          9. -
        -
        5. -
      -
      7. -
    -
    9. -
-
- -
-

21.2.5.6 get RegExp.prototype.multiline

- -

RegExp.prototype.multiline is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    4. -
  4. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    5. -
  5. If flags is undefined, then throw a TypeError exception.
    6. -
  6. If flags contains the character "m", then return true.
    7. -
  7. Return false.
    8. -
-
- -
-

21.2.5.7 RegExp.prototype.replace ( string, replaceValue )

- -

When the replace method is called with arguments string and replaceValue the - following steps are taken:

- -
    -
  1. Let rx be the this value.
    2. -
  2. If Type(rx) is not Object, then throw a TypeError - exception.
    3. -
  3. Let nCaptures be the number of left capturing parentheses in rx (using NcapturingParens as - specified in 21.2.2.1)
    4. -
  4. Let S be ToString(string).
    5. -
  5. ReturnIfAbrupt(S).
    6. -
  6. Let lengthS be the number of code unit elements in S.
    7. -
  7. Let functionalReplace be IsCallable(replaceValue).
    8. -
  8. If functionReplace is false, then -
      -
    1. Let replaceValue be ToString(replaceValue).
      2. -
    2. ReturnIfAbrupt(replaceValue)..
      3. -
    -
    9. -
  9. Let global be ToBoolean(Get(rx, - "global")).
    10. -
  10. ReturnIfAbrupt(global).
    11. -
  11. If global is true, then -
      -
    1. Let putStatus be Put(rx, "lastIndex", 0, - true).
      2. -
    2. ReturnIfAbrupt(putStatus).
      3. -
    -
    12. -
  12. Let previousLastIndex be 0.
    13. -
  13. Let results be a new empty List.
    14. -
  14. Let done be false.
    15. -
  15. Repeat, while done is false -
      -
    1. Let result be RegExpExec(rx, S).
      2. -
    2. ReturnIfAbrupt(result).
      3. -
    3. If result is null, then set done to true.
      4. -
    4. Else result is not null, -
        -
      1. If global is false, then set done to true.
        2. -
      2. Else, -
          -
        1. Let thisIndex be ToInteger(Get(rx, - "lastIndex")).
          2. -
        2. ReturnIfAbrupt(thisIndex).
          3. -
        3. If thisIndex = previousLastIndex then -
            -
          1. Let putStatus be Put(rx, "lastIndex", - thisIndex+1, true).
            2. -
          2. ReturnIfAbrupt(putStatus).
            3. -
          3. Set previousLastIndex to thisIndex+1.
            4. -
          -
          4. -
        4. Else, -
            -
          1. Set previousLastIndex to thisIndex.
            2. -
          -
          5. -
        -
        3. -
      -
      5. -
    5. If result is not null, then append result to the end of results.
      6. -
    -
    16. -
  16. Let accumulatedResult be the empty String value.
    17. -
  17. Let nextSrcPosition be 0.
    18. -
  18. Let done be false.
    19. -
  19. Repeat, for each result in results, -
      -
    1. Let matched be ToString(Get(result, - "0")).
      2. -
    2. ReturnIfAbrupt(matched).
      3. -
    3. Let matchLength be the number of code units in matched.
      4. -
    4. Let position be ToInteger(Get(result, - "index")).
      5. -
    5. ReturnIfAbrupt(position).
      6. -
    6. Let position be max(min(position, lengthS), 0).
      7. -
    7. Let n be 1.
      8. -
    8. Let captures be an empty List.
      9. -
    9. Repeat while n ≤ nCaptures -
        -
      1. Let capN be Get(result, ToString(n)).
        2. -
      2. If Type(capN) is not Undefined, then let - capN be ToString(capN).
        3. -
      3. ReturnIfAbrupt(capN).
        4. -
      4. Append capN as the last element of captures.
        5. -
      5. Let n be n+1
        6. -
      -
      10. -
    10. If functionalReplace is true, then -
        -
      1. Let replacerArgs be the List - (matched).
        2. -
      2. Append in list order the elements of captures to the end of the List replacerArgs.
        3. -
      3. Append position and S as the last two elements of replacerArgs.
        4. -
      4. Let replValue be the result of calling the [[Call]] internal method of replaceValue passing - undefined as the this value and replacerArgs as the argument list.
        5. -
      5. Let replacement be ToString(replValue).
        6. -
      -
      11. -
    11. Else, -
        -
      1. Let replacement be GetReplaceSubstitution(matched, - S, position, captures, replaceValue).
        2. -
      -
      12. -
    12. ReturnIfAbrupt(replacement).
      13. -
    13. If position ≥ nextSourcePosition, then -
        -
      1. NOTE position should not normally move backwards. If it does, it is in indication of a - ill-behaving RegExp subclass or use of an access triggered side-effect to change the global flag or other - characteristics of rx. In such cases, the corresponding substitution is ignored.
        2. -
      2. Let accumulatedResult be the String formed by concatenating the code units of the current value of - accumulatedResult with the substring of S consisting of the code units from - nextSrcPosition (inclusive) up to position (exclusive) and with the code units of - replacement.
        3. -
      3. Let nextSrcPosition be position + matchLength.
        4. -
      -
      14. -
    -
    20. -
  20. If nextSrcPosition ≥ the number of code units in S, then return accumulatedResult.
    21. -
  21. Return the String formed by concatenating the code units of accumulatedResult with the substring of S - consisting of the code units from nextSrcPosition (inclusive) up through the final code unit of S - (inclusive).
    22. -
-
- -
-

21.2.5.8 RegExp.prototype.search ( string )

- -

When the search method is called with argument string, the following steps are taken:

- -
    -
  1. Let rx be the this value.
    2. -
  2. If Type(rx) is not Object, then throw a TypeError - exception.
    3. -
  3. Let s be ToString(string).
    4. -
  4. ReturnIfAbrupt(s).
    5. -
  5. Let previousLastIndex be Get(rx, "lastIndex").
    6. -
  6. ReturnIfAbrupt(previousLastIndex).
    7. -
  7. Let status be Put(rx, "lastIndex", 0, - true)
    8. -
  8. ReturnIfAbrupt(status)
    9. -
  9. Let result be RegExpExec(rx, s).
    10. -
  10. ReturnIfAbrupt(result).
    11. -
  11. Let status be Put(rx, "lastIndex", - previousLastIndex, true)
    12. -
  12. ReturnIfAbrupt(status)
    13. -
  13. If result is null, return –1.
    14. -
  14. Return Get(result, "index").
    15. -
- -
-

NOTE The lastIndex and global properties of this RegExp object are - ignored when performing the search. The lastIndex property is left unchanged.

-
-
- -
-

21.2.5.9 get RegExp.prototype.source

- -

RegExp.prototype.source is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalSource]] internal - slot throw a TypeError exception.
    4. -
  4. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    5. -
  5. Let src be the value of R’s [[OriginalSource]] internal slot.
    6. -
  6. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    7. -
  7. If either src or flags is undefined, then throw a TypeError exception.
    8. -
  8. Return EscapeRegExpPattern(src, flags).
    9. -
-
- -
-

21.2.5.10 RegExp.prototype.split ( string, limit )

- -
-

NOTE Returns an Array object into which substrings of the result of converting string - to a String have been stored. The substrings are determined by searching from left to right for matches of the - this value regular expression; these occurrences are not part of any substring in the returned array, but serve - to divide up the String value.

- -

The this value may be an empty regular expression or a regular expression that can match an empty String. In - this case, regular expression does not match the empty substring at the - beginning or end of the input String, nor does it match the empty substring at the end of the previous separator match. - (For example, if the regular expression matches the empty String, the String is split up into individual code unit - elements; the length of the result array equals the length of the String, and each substring contains one code unit.) - Only the first match at a given position of the this String is considered, even if backtracking could yield a - non-empty-substring match at that position. (For example, /a*?/.split("ab") evaluates to the array - ["a","b"], while /a*/.split("ab") evaluates to the array["","b"].)

- -

If the string is (or converts to) the empty String, the result depends on whether the regular expression can - match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one - element, which is the empty String.

- -

If the regular expression that contains capturing parentheses, then each time separator is matched the results - (including any undefined results) of the capturing parentheses are spliced into the output array. - For example,

- -

/<(\/)?([^<>]+)>/.split("A<B>bold</B>and<CODE>coded</CODE>")

- -

evaluates to the array

- -

["A", undefined, "B", "bold", "/", "B", "and", undefined,"CODE", "coded", "/", - "CODE", ""]

- -

If limit is not undefined, then the output array is truncated so that it contains no more than - limit elements.

-
- -

When the split method is called, the following steps are taken:

- -
    -
  1. Let rx be the this value.
    2. -
  2. If Type(rx) is not Object, then throw a TypeError - exception.
    3. -
  3. If rx does not have a [[RegExpMatcher]] internal - slot, then throw a TypeError exception.
    4. -
  4. If the value of rx’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
    5. -
  5. Let matcher be the value of rx’s [[RegExpMatcher]] internal slot.
    6. -
  6. Let S be ToString(string).
    7. -
  7. ReturnIfAbrupt(S).
    8. -
  8. Let A be the result of the abstract operation ArrayCreate with argument - 0.
    9. -
  9. ReturnIfAbrupt(A).
    10. -
  10. Let lengthA be 0.
    11. -
  11. If limit is undefined, let lim = 253–1; else let lim = ToLength(limit).
    12. -
  12. Let s be the number of elements in S.
    13. -
  13. Let p = 0.
    14. -
  14. If lim = 0, return A.
    15. -
  15. If s = 0, then -
      -
    1. Let z be the result of calling the matcher with arguments S and 0.
      2. -
    2. ReturnIfAbrupt(z).
      3. -
    3. If z is not failure, return A.
      4. -
    4. Assert: The following call will never result in an abrupt completion.
      5. -
    5. Call CreateDataProperty(A, "0", - S).
      6. -
    6. Return A.
      7. -
    -
    16. -
  16. Let q = p.
    17. -
  17. Repeat, while q ≠ s -
      -
    1. Let z be the result of calling the matcher with arguments S and q
      2. -
    2. ReturnIfAbrupt(z).
      3. -
    3. If z is failure, then let q = q+1.
      4. -
    4. Else z is not failure, -
        -
      1. z must be a State. Let e be z's endIndex and let cap be z's - captures List.
        2. -
      2. If e = p, then let q = q+1.
        3. -
      3. Else e ≠ p, -
          -
        1. Let T be a String value equal to the substring of S consisting of the elements at - positions p (inclusive) through q (exclusive).
          2. -
        2. Assert: The following call will never result in an abrupt completion.
          3. -
        3. Call CreateDataProperty(A, ToString(lengthA), T).
          4. -
        4. If lengthA = lim, return A.
          5. -
        5. Let p = e.
          6. -
        6. Let i = 0.
          7. -
        7. Repeat, while i is not equal to the number of elements in cap. -
            -
          1. Let i = i+1.
            2. -
          2. Assert: The following call will never result in an abrupt completion.
            3. -
          3. Call CreateDataProperty(A, ToString(lengthA), cap[i]).
            4. -
          4. Increment lengthA by 1.
            5. -
          5. If lengthA = lim, return A.
            6. -
          -
          8. -
        8. Let q = p.
          9. -
        -
        4. -
      -
      5. -
    -
    18. -
  18. Let T be a String value equal to the substring of S consisting of the elements at positions p - (inclusive) through s (exclusive).
    19. -
  19. Assert: The following call will never result in an abrupt completion.
    20. -
  20. Call CreateDataProperty(A, ToString(lengthA), T ).
    21. -
  21. Return A.
    22. -
- -

The length property of the split method is 2.

- -
-

NOTE 1 The split method ignores the value of the global property of - this RegExp object.

-
-
- -
-

21.2.5.11 get RegExp.prototype.sticky

- -

RegExp.prototype.sticky is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    4. -
  4. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    5. -
  5. If flags is undefined, then throw a TypeError exception.
    6. -
  6. If flags contains the character "y", then return true.
    7. -
  7. Return false.
    8. -
-
- -
-

21.2.5.12 RegExp.prototype.test( S )

- -

The following steps are taken:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. Let string be ToString(S).
    4. -
  4. ReturnIfAbrupt(string).
    5. -
  5. Let match be RegExpExec(R, string).
    6. -
  6. ReturnIfAbrupt(match).
    7. -
  7. If match is not null, then return true; else return false.
    8. -
-
- -
-

21.2.5.13 RegExp.prototype.toString ( )

-
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have a [[RegExpMatcher]] internal - slot, then throw a TypeError exception.
    4. -
  4. If the value of R’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
    5. -
  5. Let pattern be ToString(Get(R, - "source")).
    6. -
  6. ReturnIfAbrupt(pattern).
    7. -
  7. Let result be the String value formed by concatenating "/", pattern, and - "/".
    8. -
  8. Let global be ToBoolean(Get(R, - "global")).
    9. -
  9. ReturnIfAbrupt(global).
    10. -
  10. If global is true, then append "g" as the last character of result.
    11. -
  11. Let ignoreCase be ToBoolean(Get(R, - "ignoreCase")).
    12. -
  12. ReturnIfAbrupt(ignoreCase).
    13. -
  13. If ignoreCase is true, then append "i" as the last character of result.
    14. -
  14. Let multiline be ToBoolean(Get(R, - "multiline")).
    15. -
  15. ReturnIfAbrupt(multiline).
    16. -
  16. If multiline is true, then append "m" as the last character of result.
    17. -
  17. Let unicode be ToBoolean(Get(R, - "unicode")).
    18. -
  18. ReturnIfAbrupt(unicode).
    19. -
  19. If unicode is true, then append "u" as the last character of result.
    20. -
  20. Let sticky be ToBoolean(Get(R, - "sticky")).
    21. -
  21. ReturnIfAbrupt(sticky).
    22. -
  22. If sticky is true, then append "y" as the last character of result.
    23. -
  23. Return result.
    24. -
- -
-

NOTE The returned String has the form of a RegularExpressionLiteral that evaluates to - another RegExp object with the same behaviour as this object.

-
-
- -
-

21.2.5.14 get RegExp.prototype.unicode

- -

RegExp.prototype.unicode is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let R be the this value.
    2. -
  2. If Type(R) is not Object, then throw a TypeError - exception.
    3. -
  3. If R does not have an [[OriginalFlags]] internal - slot throw a TypeError exception.
    4. -
  4. Let flags be the value of R’s [[OriginalFlags]] internal slot.
    5. -
  5. If flags is undefined, then throw a TypeError exception.
    6. -
  6. If flags contains the character "u", then return true.
    7. -
  7. Return false.
    8. -
-
- -
-

21.2.5.15 RegExp.prototype [ @@isRegExp ]

- -

The initial value of the @@isRegExp property is true.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE The @@isRegExp property is used by String.prototype methods to identify - objects that have the basic behaviour of regular expressions. The absence of a @@isRegExp property or the existence of - such a property whose value is null indicates that the object should is not intended to be used as regular - expression object.

-
-
-
- -
-
-

21.2.6 Properties of RegExp Instances

- -

RegExp instances are ordinary objects that inherit properties from the RegExp prototype object. RegExp instances have - internal slots [[RegExpMatcher]], [[OriginalSource]], and [[OriginalFlags]]. The value of the [[RegExpMatcher]] internal - slot is an implementation dependent representation of the Pattern of the RegExp object.

- -
-

NOTE Prior to the 6th Edition, RegExp instances were specified as - having the own data properties source, global, ignoreCase, and - multiline. Those properties are now specified as accessor properties of RegExp.prototype.

-
- -

RegExp instances also have the following property:

-
- -
-

21.2.6.1 - lastIndex

- -

The value of the lastIndex property specifies the String position at which to start the next match. It is - coerced to an integer when used (see 21.2.5.2). This property shall have the - attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.

-
-
-
-
- -
-
-

22 Indexed - Collections

-
- -
-
-

22.1 Array - Objects

- -

Array objects are exotic objects that give special treatment to a certain class of property names. See 9.4.1.4 for a definition of this special treatment.

- -

An Array object, O, is said to be sparse if the following algorithm returns true:

- -
    -
  1. Let len be Get(O, "length").
    2. -
  2. For each integer i in the range 0≤i<ToUint32(len) -
      -
    1. Let elem be the result of calling the [[GetOwnProperty]] internal method of O with argument ToString(i).
      2. -
    2. If elem is undefined, return true.
      3. -
    -
    3. -
  3. Return false.
    4. -
-
- -
-
-

22.1.1 - The Array Constructor

- -

The Array constructor is the %Array% intrinsic object and the initial value of the Array property of the - global object. When Array is called as a function rather than as a constructor, it creates and initializes a - new Array object. Thus the function call Array(…) is equivalent to the object creation - expression new Array(…) with the same arguments. However, if the this value - passed in the call is an Object with an [[ArrayInitializationState]] internal slot whose value is undefined, it initializes the this value using the argument values. This permits - Array to be used both as factory method and to perform constructor instance initialization.

- -

The Array constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - Array behaviour must include a super call to the Array constructor to initialize - subclass instances.

- -

The length property of the Array constructor function is 1.

-
- -
-

22.1.1.1 Array ( )

- -

This description applies if and only if the Array constructor is called with no arguments.

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs = 0.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has an - [[ArrayInitializationState]] internal slot and the - value of [[ArrayInitializationState]] is false, then -
      -
    1. Set the value of O’s [[ArrayInitializationState]] internal slot to true.
      2. -
    2. Let array be O.
      3. -
    -
    5. -
  5. Else, -
      -
    1. Let F be this function.
      2. -
    2. Let proto be GetPrototypeFromConstructor(F, - "%ArrayPrototype%").
      3. -
    3. ReturnIfAbrupt(proto).
      4. -
    4. Let array be ArrayCreate(0, proto).
      5. -
    -
    6. -
  6. ReturnIfAbrupt(array).
    7. -
  7. Let putStatus be Put(array, "length", 0, - true).
    8. -
  8. ReturnIfAbrupt(putStatus).
    9. -
  9. Return array.
    10. -
-
- -
-

22.1.1.2 Array - (len)

- -

This description applies if and only if the Array constructor is called with exactly one argument.

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs = 1.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has an - [[ArrayInitializationState]] internal slot and the - value of [[ArrayInitializationState]] is false, then -
      -
    1. Set the value of O’s [[ArrayInitializationState]] internal slot to true.
      2. -
    2. Let array be O.
      3. -
    -
    5. -
  5. Else, -
      -
    1. Let F be this function.
      2. -
    2. Let proto be GetPrototypeFromConstructor(F, - "%ArrayPrototype%").
      3. -
    3. ReturnIfAbrupt(proto).
      4. -
    4. Let array be ArrayCreate(0, proto).
      5. -
    -
    6. -
  6. ReturnIfAbrupt(array).
    7. -
  7. If Type(len) is not Number, then -
      -
    1. Let defineStatus be CreateDataPropertyOrThrow(array, - "0", len).
      2. -
    2. ReturnIfAbrupt(defineStatus).
      3. -
    3. Let intLen be 1.
      4. -
    -
    8. -
  8. Else, -
      -
    1. Let intLen be ToUint32(len).
      2. -
    2. If intLen ≠ len, then throw a RangeError exception.
      3. -
    -
    9. -
  9. Let putStatus be Put(array, "length", intLen, - true).
    10. -
  10. ReturnIfAbrupt(putStatus).
    11. -
  11. Return array.
    12. -
-
- -
-

22.1.1.3 - Array (...items )

- -

This description applies if and only if the Array constructor is called with at least two arguments.

- -

When the Array function is called the following steps are taken:

- -
    -
  1. Let numberOfArgs be the number of arguments passed to this function call.
    2. -
  2. Assert: numberOfArgs ≥ 2.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is Object and O has an - [[ArrayInitializationState]] internal slot and the - value of [[ArrayInitializationState]] is false, then -
      -
    1. Set the value of O’s [[ArrayInitializationState]] internal slot to true.
      2. -
    2. Let array be O.
      3. -
    -
    5. -
  5. Else, -
      -
    1. Let F be this function.
      2. -
    2. Let proto be GetPrototypeFromConstructor(F, - "%ArrayPrototype%").
      3. -
    3. ReturnIfAbrupt(proto).
      4. -
    4. Let array be ArrayCreate(numberOfArgs, proto).
      5. -
    -
    6. -
  6. ReturnIfAbrupt(array).
    7. -
  7. Let k be 0.
    8. -
  8. Let items be a zero-origined List containing the - argument items in order.
    9. -
  9. Repeat, while k < numberOfArgs -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let itemK be kth element of items.
      3. -
    3. Let defineStatus be CreateDataPropertyOrThrow(array, - Pk, itemK).
      4. -
    4. ReturnIfAbrupt(defineStatus).
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Let putStatus be Put(array, "length", - numberOfArgs, true).
    11. -
  11. ReturnIfAbrupt(putStatus).
    12. -
  12. Return array.
    13. -
-
- -
-

22.1.1.4 new Array ( ... argumentsList)

- -

When Array is called as part of a new expression, it initializes a newly created object.

- -
    -
  1. Let F be the Array function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If Array is implemented as an ECMAScript function object, - its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

22.1.2 Properties of the Array Constructor

- -

The value of the [[Prototype]] internal slot of the Array - constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Array constructor has the following - properties:

-
- -
-

22.1.2.1 - Array.from ( arrayLike [ , mapfn [ , thisArg ] ] )

- -

When the from method is called with argument arrayLike and optional arguments mapfn - and thisArg the following steps are taken:

- -
    -
  1. Let C be the this value.
    2. -
  2. Let items be ToObject(arrayLike).
    3. -
  3. ReturnIfAbrupt(items).
    4. -
  4. If mapfn is undefined, then let mapping be false.
    5. -
  5. else -
      -
    1. If IsCallable(mapfn) is false, throw a TypeError - exception.
      2. -
    2. If thisArg was supplied, let T be thisArg; else let T be undefined.
      3. -
    3. Let mapping be true
      4. -
    -
    6. -
  6. Let usingIterator be CheckIterable(items).
    7. -
  7. ReturnIfAbrupt(usingIterator).
    8. -
  8. If usingIterator is not undefined, then -
      -
    1. If IsConstructor(C) is true, then -
        -
      1. Let A be the result of calling the [[Construct]] internal method of C with an empty argument - list.
        2. -
      -
      2. -
    2. Else, -
        -
      1. Let A be ArrayCreate(0).
        2. -
      -
      3. -
    3. ReturnIfAbrupt(A).
      4. -
    4. Let iterator be GetIterator(items, usingIterator).
      5. -
    5. ReturnIfAbrupt(iterator).
      6. -
    6. Let k be 0.
      7. -
    7. Repeat -
        -
      1. Let Pk be ToString(k).
        2. -
      2. Let next be IteratorStep(iterator).
        3. -
      3. ReturnIfAbrupt(next).
        4. -
      4. If next is false, then -
          -
        1. Let putStatus be Put(A, "length", - k, true).
          2. -
        2. ReturnIfAbrupt(putStatus).
          3. -
        3. Return A.
          4. -
        -
        5. -
      5. Let nextValue be IteratorValue(next).
        6. -
      6. ReturnIfAbrupt(nextValue).
        7. -
      7. If mapping is true, then -
          -
        1. Let mappedValue be the result of calling the [[Call]] internal method of mapfn with - T as thisArgument and (nextValue, k) as argumentsList.
          2. -
        2. ReturnIfAbrupt(mappedValue).
          3. -
        -
        8. -
      8. Else, let mappedValue be nextValue.
        9. -
      9. Let defineStatus be CreateDataPropertyOrThrow(A, - Pk, mappedValue).
        10. -
      10. ReturnIfAbrupt(defineStatus).
        11. -
      11. Increase k by 1.
        12. -
      -
      8. -
    -
    9. -
  9. Assert: items is not an Iterator so assume it is an array-like - object.
    10. -
  10. Let lenValue be Get(items, "length").
    11. -
  11. Let len be ToLength(lenValue).
    12. -
  12. ReturnIfAbrupt(len).
    13. -
  13. If IsConstructor(C) is true, then -
      -
    1. Let A be the result of calling the [[Construct]] internal method of C with an argument list - containing the single item len.
      2. -
    -
    14. -
  14. Else, -
      -
    1. Let A be ArrayCreate(len).
      2. -
    -
    15. -
  15. ReturnIfAbrupt(A).
    16. -
  16. Let k be 0.
    17. -
  17. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(items, Pk).
      3. -
    3. ReturnIfAbrupt(kValue).
      4. -
    4. If mapping is true, then -
        -
      1. Let mappedValue be the result of calling the [[Call]] internal method of mapfn with T - as thisArgument and (kValue, k) as argumentsList.
        2. -
      2. ReturnIfAbrupt(mappedValue).
        3. -
      -
      5. -
    5. Else, let mappedValue be kValue.
      6. -
    6. Let defineStatus be CreateDataPropertyOrThrow(A, - Pk, mappedValue).
      7. -
    7. ReturnIfAbrupt(defineStatus).
      8. -
    8. Increase k by 1.
      9. -
    -
    18. -
  18. Let putStatus be Put(A, "length", len, - true).
    19. -
  19. ReturnIfAbrupt(putStatus).
    20. -
  20. Return A.
    21. -
- -

The length property of the from method is 1.

- -
-

NOTE The from function is an intentionally generic factory method; it does not - require that its this value be the Array constructor. Therefore it can be transferred to or inherited by any - other constructors that may be called with a single numeric argument.

-
-
- -
-

22.1.2.2 - Array.isArray ( arg )

- -

The isArray function takes one argument arg, and performs the following:

- -
    -
  1. If Type(arg) is not Object, return false.
    2. -
  2. If arg is an exotic Array object, then return true.
    3. -
  3. Return false.
    4. -
-
- -
-

22.1.2.3 - Array.of ( ...items )

- -

When the of method is called with any number of arguments, the following steps are taken:

- -
    -
  1. Let len be the actual number of arguments passed to this function.
    2. -
  2. Let items be the List of arguments passed to this - function.
    3. -
  3. Let C be the this value.
    4. -
  4. If IsConstructor(C) is true, then -
      -
    1. Let A be the result of calling the [[Construct]] internal method of C with an argument list - containing the single item len.
      2. -
    -
    5. -
  5. Else, -
      -
    1. Let A be ArrayCreate(len).
      2. -
    -
    6. -
  6. ReturnIfAbrupt(A).
    7. -
  7. Let k be 0.
    8. -
  8. Repeat, while k < len -
      -
    1. Let kValue be element k of items.
      2. -
    2. Let defineStatus be CreateDataPropertyOrThrow(A,Pk, - kValue.[[value]]).
      3. -
    3. ReturnIfAbrupt(defineStatus).
      4. -
    4. Increase k by 1.
      5. -
    -
    9. -
  9. Let putStatus be Put(A, "length", len, - true).
    10. -
  10. ReturnIfAbrupt(putStatus).
    11. -
  11. Return A.
    12. -
- -

The length property of the of method is 0.

- -
-

NOTE 1 The items argument is assumed to be a well-formed rest argument value.

-
- -
-

NOTE 2 The of function is an intentionally generic factory method; it does not - require that its this value be the Array constructor. Therefore it can be transferred to or inherited by other - constructors that may be called with a single numeric argument.

-
-
- -
-

22.1.2.4 - Array.prototype

- -

The value of Array.prototype is %ArrayPrototype%, the intrinsic Array prototype object (22.1.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

22.1.2.5 - Array[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let proto be GetPrototypeFromConstructor(F, - "%ArrayPrototype%").
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Let obj be ArrayCreate(undefined, proto).
    5. -
  5. Return obj.
    6. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

- -
-

NOTE 1 Passing undefined as the first argument to ArrayCreate causes the [[ArrayInitializationState]] internal slot of the array to be initially assigned the value - false. This is a flag used to indicate that the instance has not yet been initialized by the Array - constructor. This flag value is never directly exposed to ECMAScript code; hence implementations may choose to encode - the flag in any unobservable manner.

-
- -
-

NOTE 2 The Array @@create function is intentionally generic; it does not require - that its this value be the Array constructor object. It can be transferred to other constructor functions for use - as a @@create method. When used with other constructors, this function will create an exotic Array object - whose [[Prototype]] value is obtained from the associated constructor.

-
-
-
- -
-
-

22.1.3 Properties of the Array Prototype Object

- -

The value of the [[Prototype]] internal slot of the Array - prototype object is the intrinsic object %ObjectPrototype%.

- -

The Array prototype object is itself an ordinary object. It is not an Array instance and does not have a - length property .

- -
-

NOTE The Array prototype object does not have a valueOf property of its own; - however, it inherits the valueOf property from the standard built-in Object prototype Object.

-
-
- -
-
-

22.1.3.1 Array.prototype.concat ( ...arguments )

- -

When the concat method is called with zero or more arguments, it returns an array containing the array - elements of the object followed by the array elements of each argument in order.

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let A be undefined.
    4. -
  4. If O is an exotic Array object, then -
      -
    1. Let C be Get(O, "constructor").
      2. -
    2. ReturnIfAbrupt(C).
      3. -
    3. If IsConstructor(C) is true, then -
        -
      1. Let thisRealm be the running execution context’s Realm.
        2. -
      2. If thisRealm and the value of C’s [[Realm]] internal slot are the same value, then -
          -
        1. Let A be the result of calling the [[Construct]] internal method of C with argument - (0).
          2. -
        -
        3. -
      -
      4. -
    -
    5. -
  5. If A is undefined, then -
      -
    1. Let A be ArrayCreate(0).
      2. -
    -
    6. -
  6. ReturnIfAbrupt(A).
    7. -
  7. Let n be 0.
    8. -
  8. Let items be a List whose first element is O - and whose subsequent elements are, in left to right order, the arguments that were passed to this function - invocation.
    9. -
  9. Repeat, while items is not empty -
      -
    1. Remove the first element from items and let E be the value of the element.
      2. -
    2. Let spreadable be IsConcatSpreadable(E).
      3. -
    3. ReturnIfAbrupt(spreadable).
      4. -
    4. If spreadable is true, then -
        -
      1. Let k be 0.
        2. -
      2. Let lenVal be Get(E, "length").
        3. -
      3. Let len be ToLength(lenVal).
        4. -
      4. ReturnIfAbrupt(len).
        5. -
      5. Repeat, while k < len -
          -
        1. Let P be ToString(k).
          2. -
        2. Let exists be HasProperty(E, P).
          3. -
        3. ReturnIfAbrupt(exists).
          4. -
        4. If exists is true, then -
            -
          1. Let subElement be Get(E, P).
            2. -
          2. ReturnIfAbrupt(subElement).
            3. -
          3. Let status be CreateDataPropertyOrThrow - (A, ToString(n), subElement).
            4. -
          4. ReturnIfAbrupt(status).
            5. -
          -
          5. -
        5. Increase n by 1.
          6. -
        6. Increase k by 1.
          7. -
        -
        6. -
      -
      5. -
    5. Else E is added as a single item rather than spread, -
        -
      1. Let status be CreateDataPropertyOrThrow (A, ToString(n), E).
        2. -
      2. ReturnIfAbrupt(status).
        3. -
      3. Increase n by 1.
        4. -
      -
      6. -
    -
    10. -
  10. Let putStatus be Put(A, "length", n, - true).
    11. -
  11. ReturnIfAbrupt(putStatus).
    12. -
  12. Return A.
    13. -
- -

The length property of the concat method is 1.

- -
-

NOTE 1 The explicit setting of the length property in step 10 is necessary to - ensure that its value is correct in situations where the trailing elements of the result Array are not present.

-
- -
-

NOTE 2 The concat function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a - method. Whether the concat function can be applied successfully to an exotic object that is not an Array - is implementation-dependent.

-
-
- -
-

22.1.3.1.1 IsConcatSpreadable ( O ) Abstract Operation

- -

The abstract operation IsConcatSpreadable with argument O performs the following steps:

- -
    -
  1. If Type(O) is not Object, then return - false.
    2. -
  2. Let spreadable be Get(O, @@isConcatSpreadable).
    3. -
  3. ReturnIfAbrupt(spreadable).
    4. -
  4. If spreadable is not undefined, then return ToBoolean(spreadable).
    5. -
  5. If O is an exotic Array object, then return true.
    6. -
  6. Return false.
    7. -
-
-
- -
-

22.1.3.2 Array.prototype.constructor

- -

The initial value of Array.prototype.constructor is the standard built-in Array - constructor.

-
- -
-

22.1.3.3 Array.prototype.copyWithin (target, start [ , end ] )

- -

The copyWithin method takes up to three arguments target, start and - end.

- -
-

NOTE The end argument is optional with the length of the this object as its - default value. If target is negative, it is treated as length+target where length is the - length of the array. If start is negative, it is treated as length+start. If end is - negative, it is treated as length+end.

-
- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let relativeTarget be ToInteger(target).
    7. -
  7. ReturnIfAbrupt(relativeTarget).
    8. -
  8. If relativeTarget is negative, let to be max((len + relativeTarget),0); else let - to be min(relativeTarget, len).
    9. -
  9. Let relativeStart be ToInteger(start).
    10. -
  10. ReturnIfAbrupt(relativeStart).
    11. -
  11. If relativeStart is negative, let from be max((len + relativeStart),0); else let - from be min(relativeStart, len).
    12. -
  12. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
    13. -
  13. ReturnIfAbrupt(relativeEnd).
    14. -
  14. If relativeEnd is negative, let final be max((len + relativeEnd),0); else let - final be min(relativeEnd, len).
    15. -
  15. Let count be min(final-from, len-to).
    16. -
  16. If from<to and to<from+count -
      -
    1. Let direction = -1.
      2. -
    2. Let from = from + count -1.
      3. -
    3. Let to = to + count -1.
      4. -
    -
    17. -
  17. Else, -
      -
    1. Let direction = 1.
      2. -
    -
    18. -
  18. Repeat, while count > 0 -
      -
    1. Let fromKey be ToString(from).
      2. -
    2. Let toKey be ToString(to).
      3. -
    3. Let fromPresent be HasProperty(O, fromKey).
      4. -
    4. ReturnIfAbrupt(fromPresent).
      5. -
    5. If fromPresent is true, then -
        -
      1. Let fromVal be Get(O, fromKey).
        2. -
      2. ReturnIfAbrupt(fromVal).
        3. -
      3. Let putStatus be Put(O, toKey, fromVal, - true).
        4. -
      4. ReturnIfAbrupt(putStatus).
        5. -
      -
      6. -
    6. Else fromPresent is false, -
        -
      1. Let deleteStatus be DeletePropertyOrThrow(O, - toKey).
        2. -
      2. ReturnIfAbrupt(deleteStatus).
        3. -
      -
      7. -
    7. Let from be from + direction.
      8. -
    8. Let to be to + direction.
      9. -
    9. Let count be count − 1.
      10. -
    -
    19. -
  19. Return O.
    20. -
- -

The length property of the copyWithin method is 2.

- -
-

NOTE 1 The copyWithin function is intentionally generic; it does not require - that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a - method. Whether the copyWithin function can be applied successfully to an exotic object that is not an - Array is implementation-dependent.

-
-
- -
-

22.1.3.4 Array.prototype.entries ( )

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject with the this value as its - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Return CreateArrayIterator(O, "key+value").
    4. -
-
- -
-

22.1.3.5 Array.prototype.every ( callbackfn [ , thisArg] )

- -

NOTE callbackfn should be a function that accepts - three arguments and returns a value that is coercible to the Boolean value true or false. every - calls callbackfn once for each element present in the array, in ascending order, until it finds one where - callbackfn returns false. If such an element is found, every immediately returns false. - Otherwise, if callbackfn returned true for all elements, every will return true. - callbackfn is called only for elements of the array which actually exist; it is not called for missing elements of - the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

every does not directly mutate the object on which it is called but the object may be mutated - by the calls to callbackfn.

- -

The range of elements processed by every is set before the first call to callbackfn. - Elements which are appended to the array after the call to every begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to callbackfn will be the - value at the time every visits them; elements that are deleted after the call to every begins - and before being visited are not visited. every acts like the "for all" quantifier in mathematics. In - particular, for an empty array, it returns true.

- -

When the every method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length")
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let k be 0.
    9. -
  9. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let testResult be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(testResult).
        5. -
      5. If ToBoolean(testResult) is false, return false.
        6. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Return true.
    11. -
- -

The length property of the every method is 1.

- -
-

NOTE The every function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the every function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.6 Array.prototype.fill (value [ , start [ , end ] ] )

- -

The fill method takes up to three arguments value, start and end.

- -
-

NOTE The start and end arguments are optional with default values of 0 and the - length of the this object. If start is negative, it is treated as length+start where - length is the length of the array. If end is negative, it is treated as length+end.

-
- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let relativeStart be ToInteger(start).
    7. -
  7. ReturnIfAbrupt(relativeStart).
    8. -
  8. If relativeStart is negative, let k be max((len + relativeStart),0); else let k - be min(relativeStart, len).
    9. -
  9. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
    10. -
  10. ReturnIfAbrupt(relativeEnd).
    11. -
  11. If relativeEnd is negative, let final be max((len + relativeEnd),0); else let - final be min(relativeEnd, len).
    12. -
  12. Repeat, while k < final -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let putStatus be Put(O, Pk, value, - true).
      3. -
    3. ReturnIfAbrupt(putStatus).
      4. -
    4. Increase k by 1.
      5. -
    -
    13. -
  13. Return O.
    14. -
- -

The length property of the fill method is 1.

- -
-

NOTE 1 The fill function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the fill function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.7 Array.prototype.filter ( callbackfn [ , thisArg ] )

- -

NOTE callbackfn should be a function that accepts - three arguments and returns a value that is coercible to the Boolean value true or false. - filter calls callbackfn once for each element in the array, in ascending order, and constructs a new - array of all the values for which callbackfn returns true. callbackfn is called only for elements of - the array which actually exist; it is not called for missing elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

filter does not directly mutate the object on which it is called but the object may be - mutated by the calls to callbackfn.

- -

The range of elements processed by filter is set before the first call to callbackfn. - Elements which are appended to the array after the call to filter begins will not be visited by - callbackfn. If existing elements of the array are changed their value as passed to callbackfn will be the - value at the time filter visits them; elements that are deleted after the call to filter begins - and before being visited are not visited.

- -

When the filter method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let A be undefined.
    9. -
  9. If O is an exotic Array object, then -
      -
    1. Let C be Get(O, "constructor").
      2. -
    2. ReturnIfAbrupt(C).
      3. -
    3. If IsConstructor(C) is true, then -
        -
      1. Let thisRealm be the running execution context’s Realm.
        2. -
      2. If thisRealm and the value of C’s [[Realm]] internal slot are the same value, then -
          -
        1. Let A be the result of calling the [[Construct]] internal method of C with an argument - list containing the single item 0.
          2. -
        -
        3. -
      -
      4. -
    -
    10. -
  10. If A is undefined, then -
      -
    1. Let A be ArrayCreate(0).
      2. -
    -
    11. -
  11. ReturnIfAbrupt(A).
    12. -
  12. Let k be 0.
    13. -
  13. Let to be 0.
    14. -
  14. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let selected be the result of calling the [[Call]] internal method of callbackfn with T - as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(selected).
        5. -
      5. If ToBoolean(selected) is true, then -
          -
        1. Let status be CreateDataPropertyOrThrow (A, - ToString(to), kValue).
          2. -
        2. ReturnIfAbrupt(status).
          3. -
        3. Increase to by 1.
          4. -
        -
        6. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    15. -
  15. Return A.
    16. -
- -

The length property of the filter method is 1.

- -
-

NOTE The filter function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the filter function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.8 Array.prototype.find ( predicate [ , thisArg ] )

- -

NOTE predicate should be a function that accepts - three arguments and returns a value that is coercible to the Boolean value true or false. find - calls predicate once for each element present in the array, in ascending order, until it finds one where - predicate returns true. If such an element is found, find immediately returns that element - value. Otherwise, find returns undefined. predicate is called only for elements of the array - which actually exist; it is not called for missing elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - predicate. If it is not provided, undefined is used instead.

- -

predicate is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

find does not directly mutate the object on which it is called but the object may be mutated - by the calls to predicate.

- -

The range of elements processed by find is set before the first call to callbackfn. - Elements that are appended to the array after the call to find begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to predicate will be the - value at the time that find visits them; elements that are deleted after the call to find begins - and before being visited are not visited.

- -

When the find method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(predicate) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let k be 0.
    9. -
  9. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let testResult be the result of calling the [[Call]] internal method of predicate with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(testResult).
        5. -
      5. If ToBoolean(testResult) is true, return kValue.
        6. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Return undefined.
    11. -
- -

The length property of the find method is 1.

- -
-

NOTE The find function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the find function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.9 Array.prototype.findIndex ( predicate [ , thisArg ] )

- -

NOTE predicate should be a function that accepts - three arguments and returns a value that is coercible to the Boolean value true or false. - findIndex calls predicate once for each element present in the array, in ascending order, until it - finds one where predicate returns true. If such an element is found, findIndex immediately - returns the index of that element value. Otherwise, findIndex returns -1. predicate is called only for - elements of the array which actually exist; it is not called for missing elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - predicate. If it is not provided, undefined is used instead.

- -

predicate is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

findIndex does not directly mutate the object on which it is called but the object may be - mutated by the calls to predicate.

- -

The range of elements processed by findIndex is set before the first call to - callbackfn. Elements that are appended to the array after the call to findIndex begins will not be - visited by callbackfn. If existing elements of the array are changed, their value as passed to predicate - will be the value at the time that findIndex visits them; elements that are deleted after the call to - findIndex begins and before being visited are not visited.

- -

When the findIndex method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(predicate) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let k be 0.
    9. -
  9. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let testResult be the result of calling the [[Call]] internal method of predicate with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(testResult).
        5. -
      5. If ToBoolean(testResult) is true, return k.
        6. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Return -1.
    11. -
- -

The length property of the findIndex method is 1.

- -
-

NOTE The findIndex function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the findIndex function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.10 Array.prototype.forEach ( callbackfn [ , thisArg ] )

- -

NOTE callbackfn should be a function that accepts - three arguments. forEach calls callbackfn once for each element present in the array, in ascending - order. callbackfn is called only for elements of the array which actually exist; it is not called for missing - elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

forEach does not directly mutate the object on which it is called but the object may be - mutated by the calls to callbackfn.

- -

The range of elements processed by forEach is set before the first call to callbackfn. - Elements which are appended to the array after the call to forEach begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to callback will be the value at - the time forEach visits them; elements that are deleted after the call to forEach begins and - before being visited are not visited.

- -

When the forEach method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let k be 0.
    9. -
  9. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let funcResult be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(funcResult).
        5. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Return undefined.
    11. -
- -

The length property of the forEach method is 1.

- -
-

NOTE The forEach function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the forEach function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.11 Array.prototype.indexOf ( searchElement [ , fromIndex ] )

- -

NOTE indexOf compares searchElement - to the elements of the array, in ascending order, using the Strict Equality Comparison algorithm (7.2.11), and if found at one or more positions, returns the index of the first - such position; otherwise, −1is returned.

- -

The optional second argument fromIndex defaults to 0 (i.e. the whole array is searched). If it is - greater than or equal to the length of the array, −1is returned, i.e. the array will not be searched. If it is - negative, it is used as the offset from the end of the array to compute fromIndex. If the computed index is less - than 0, the whole array will be searched.

- -

When the indexOf method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length")
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If len is 0, return −1.
    7. -
  7. If argument fromIndex was passed let n be ToInteger(fromIndex); - else let n be 0.
    8. -
  8. ReturnIfAbrupt(n).
    9. -
  9. If n ≥ len, return −1.
    10. -
  10. If n ≥ 0, then -
      -
    1. Let k be n.
      2. -
    -
    11. -
  11. Else n<0, -
      -
    1. Let k be len - abs(n).
      2. -
    2. If k < 0, then let k be 0.
      3. -
    -
    12. -
  12. Repeat, while k<len -
      -
    1. Let kPresent be HasProperty(O, ToString(k)).
      2. -
    2. ReturnIfAbrupt(kPresent).
      3. -
    3. If kPresent is true, then -
        -
      1. Let elementK be the result of Get(O, ToString(k)).
        2. -
      2. ReturnIfAbrupt(elementK).
        3. -
      3. Let same be the result of performing Strict Equality Comparison searchElement === - elementK.
        4. -
      4. If same is true, return k.
        5. -
      -
      4. -
    4. Increase k by 1.
      5. -
    -
    13. -
  13. Return -1.
    14. -
- -

The length property of the indexOf method is 1.

- -
-

NOTE The indexOf function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the indexOf function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.12 Array.prototype.join (separator)

- -

NOTE The elements of the array are converted to Strings, - and these Strings are then concatenated, separated by occurrences of the separator. If no separator is provided, a - single comma is used as the separator.

- -

The join method takes one argument, separator, and performs the following steps:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be the result of Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If separator is undefined, let separator be the single-element String ",".
    7. -
  7. Let sep be ToString(separator).
    8. -
  8. If len is zero, return the empty String.
    9. -
  9. Let element0 be the result of Get(O, "0").
    10. -
  10. If element0 is undefined or null, let R be the empty String; otherwise, let R be - ToString(element0).
    11. -
  11. ReturnIfAbrupt(R).
    12. -
  12. Let k be 1.
    13. -
  13. Repeat, while k < len -
      -
    1. Let S be the String value produced by concatenating R and sep.
      2. -
    2. Let element be Get(O, ToString(k)).
      3. -
    3. If element is undefined or null, then let next be the empty String; otherwise, let - next be ToString(element).
      4. -
    4. ReturnIfAbrupt(next).
      5. -
    5. Let R be a String value produced by concatenating S and next.
      6. -
    6. Increase k by 1.
      7. -
    -
    14. -
  14. Return R.
    15. -
- -

The length property of the join method is 1.

- -
-

NOTE The join function is intentionally generic; it does not require that its - this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a method. - Whether the join function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.13 Array.prototype.keys ( )

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject with the this value as its - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Return CreateArrayIterator(O, "key").
    4. -
-
- -
-

22.1.3.14 Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )

- -

NOTE lastIndexOf compares - searchElement to the elements of the array in descending order using the Strict Equality Comparison algorithm (7.2.11), and if found at one or more positions, returns the index of the last - such position; otherwise, −1is returned.

- -

The optional second argument fromIndex defaults to the array's length minus one (i.e. the whole - array is searched). If it is greater than or equal to the length of the array, the whole array will be searched. If it is - negative, it is used as the offset from the end of the array to compute fromIndex. If the computed index is less - than 0, −1is returned.

- -

When the lastIndexOf method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length")
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If len is 0, return -1.
    7. -
  7. If argument fromIndex was passed let n be ToInteger(fromIndex); - else let n be len-1.
    8. -
  8. ReturnIfAbrupt(n).
    9. -
  9. If n ≥ 0, then let k be min(n, len – 1).
    10. -
  10. Else n < 0, -
      -
    1. Let k be len - abs(n).
      2. -
    -
    11. -
  11. Repeat, while k≥ 0 -
      -
    1. Let kPresent be HasProperty(O, ToString(k)).
      2. -
    2. ReturnIfAbrupt(kPresent).
      3. -
    3. If kPresent is true, then -
        -
      1. Let elementK be Get(O, ToString(k)).
        2. -
      2. ReturnIfAbrupt(elementK).
        3. -
      3. Let same be the result of performing Strict Equality Comparison
        searchElement === - elementK.
        4. -
      4. If same is true, return k.
        5. -
      -
      4. -
    4. Decrease k by 1.
      5. -
    -
    12. -
  12. Return -1.
    13. -
- -

The length property of the lastIndexOf method is 1.

- -
-

NOTE The lastIndexOf function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the lastIndexOf function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.15 Array.prototype.map ( callbackfn [ , thisArg ] )

- -

NOTE callbackfn should be a function that accepts - three arguments. map calls callbackfn once for each element in the array, in ascending order, and - constructs a new Array from the results. callbackfn is called only for elements of the array which actually exist; - it is not called for missing elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

map does not directly mutate the object on which it is called but the object may be mutated - by the calls to callbackfn.

- -

The range of elements processed by map is set before the first call to callbackfn. - Elements which are appended to the array after the call to map begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to callbackfn will be the - value at the time map visits them; elements that are deleted after the call to map begins and - before being visited are not visited.

- -

When the map method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length")
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let A be undefined.
    9. -
  9. If O is an exotic Array object, then -
      -
    1. Let C be Get(O, "constructor").
      2. -
    2. ReturnIfAbrupt(C).
      3. -
    3. If IsConstructor(C) is true, then -
        -
      1. Let thisRealm be the running execution context’s Realm.
        2. -
      2. If thisRealm and the value of C’s [[Realm]] internal slot are the same value, then -
          -
        1. Let A be the result of calling the [[Construct]] internal method of C with an argument - list containing the single item len.
          2. -
        -
        3. -
      -
      4. -
    -
    10. -
  10. If A is undefined, then -
      -
    1. Let A be ArrayCreate(len).
      2. -
    -
    11. -
  11. ReturnIfAbrupt(A).
    12. -
  12. Let k be 0.
    13. -
  13. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let mappedValue be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(mappedValue).
        5. -
      5. Let status be CreateDataPropertyOrThrow (A, - Pk, mappedValue).
        6. -
      6. ReturnIfAbrupt(status).
        7. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    14. -
  14. Return A.
    15. -
- -

The length property of the map method is 1.

- -
-

NOTE The map function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the map function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.16 Array.prototype.pop ( )

- -

NOTE The last element of the array is removed from the - array and returned.

- -

When the pop method is called the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If len is zero, -
      -
    1. Let putStatus be Put(O, "length", 0, - true).
      2. -
    2. ReturnIfAbrupt(putStatus).
      3. -
    3. Return undefined.
      4. -
    -
    7. -
  7. Else len > 0, -
      -
    1. Let newLen be len–1.
      2. -
    2. Let indx be ToString(newLen).
      3. -
    3. Let element be Get(O, indx).
      4. -
    4. ReturnIfAbrupt(element).
      5. -
    5. Let deleteStatus be DeletePropertyOrThrow(O, - indx).
      6. -
    6. ReturnIfAbrupt(deleteStatus).
      7. -
    7. Let putStatus be Put(O, "length", newLen, - true).
      8. -
    8. ReturnIfAbrupt(putStatus).
      9. -
    9. Return element.
      10. -
    -
    8. -
- -
-

NOTE The pop function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the pop function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.17 Array.prototype.push ( ...items )

- -

NOTE The arguments are appended to the end of the array, - in the order in which they appear. The new length of the array is returned as the result of the call.

- -

When the push method is called with zero or more arguments the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let n be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(n).
    6. -
  6. Let items be a List whose elements are, in left to - right order, the arguments that were passed to this function invocation.
    7. -
  7. Repeat, while items is not empty -
      -
    1. Remove the first element from items and let E be the value of the element.
      2. -
    2. Let putStatus be Put(O, ToString(n), E, true).
      3. -
    3. ReturnIfAbrupt(putStatus).
      4. -
    4. Increase n by 1.
      5. -
    -
    8. -
  8. Let putStatus be Put(O, "length", n, - true).
    9. -
  9. ReturnIfAbrupt(putStatus).
    10. -
  10. Return n.
    11. -
- -

The length property of the push method is 1.

- -
-

NOTE The push function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the push function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.18 Array.prototype.reduce ( callbackfn [ , initialValue ] )

- -

NOTE callbackfn should be a function that takes - four arguments. reduce calls the callback, as a function, once for each element present in the array, in - ascending order.

- -

callbackfn is called with four arguments: the previousValue (or value from the previous call - to callbackfn), the currentValue (value of the current element), the currentIndex, and the object - being traversed. The first time that callback is called, the previousValue and currentValue can be one of - two values. If an initialValue was provided in the call to reduce, then previousValue will be - equal to initialValue and currentValue will be equal to the first value in the array. If no - initialValue was provided, then previousValue will be equal to the first value in the array and - currentValue will be equal to the second. It is a TypeError if the array contains no elements and - initialValue is not provided.

- -

reduce does not directly mutate the object on which it is called but the object may be - mutated by the calls to callbackfn.

- -

The range of elements processed by reduce is set before the first call to callbackfn. - Elements that are appended to the array after the call to reduce begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to callbackfn will be the - value at the time reduce visits them; elements that are deleted after the call to reduce begins - and before being visited are not visited.

- -

When the reduce method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If len is 0 and initialValue is not present, throw a TypeError exception.
    8. -
  8. Let k be 0.
    9. -
  9. If initialValue is present, then -
      -
    1. Set accumulator to initialValue.
      2. -
    -
    10. -
  10. Else initialValue is not present, -
      -
    1. Let kPresent be false.
      2. -
    2. Repeat, while kPresent is false and k < len -
        -
      1. Let Pk be ToString(k).
        2. -
      2. Let kPresent be HasProperty(O, Pk).
        3. -
      3. ReturnIfAbrupt(kPresent).
        4. -
      4. If kPresent is true, then -
          -
        1. Let accumulator be Get(O, Pk).
          2. -
        2. ReturnIfAbrupt(accumulator).
          3. -
        -
        5. -
      5. Increase k by 1.
        6. -
      -
      3. -
    3. If kPresent is false, throw a TypeError exception.
      4. -
    -
    11. -
  11. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let accumulator be the result of calling the [[Call]] internal method of callbackfn with - undefined as thisArgument and a List - containing accumulator, kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(accumulator).
        5. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    12. -
  12. Return accumulator.
    13. -
- -

The length property of the reduce method is 1.

- -
-

NOTE The reduce function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the reduce function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.19 Array.prototype.reduceRight ( callbackfn [ , initialValue ] )

- -

NOTE callbackfn should be a function that takes - four arguments. reduceRight calls the callback, as a function, once for each element present in the array, in - descending order.

- -

callbackfn is called with four arguments: the previousValue (or value from the previous call - to callbackfn), the currentValue (value of the current element), the currentIndex, and the object - being traversed. The first time the function is called, the previousValue and currentValue can be one of two - values. If an initialValue was provided in the call to reduceRight, then previousValue will be - equal to initialValue and currentValue will be equal to the last value in the array. If no - initialValue was provided, then previousValue will be equal to the last value in the array and - currentValue will be equal to the second-to-last value. It is a TypeError if the array contains no elements - and initialValue is not provided.

- -

reduceRight does not directly mutate the object on which it is called but the object may be - mutated by the calls to callbackfn.

- -

The range of elements processed by reduceRight is set before the first call to - callbackfn. Elements that are appended to the array after the call to reduceRight begins will not be - visited by callbackfn. If existing elements of the array are changed by callbackfn, their value as passed to - callbackfn will be the value at the time reduceRight visits them; elements that are deleted after the - call to reduceRight begins and before being visited are not visited.

- -

When the reduceRight method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If len is 0 and initialValue is not present, throw a TypeError exception.
    8. -
  8. Let k be len-1.
    9. -
  9. If initialValue is present, then -
      -
    1. Set accumulator to initialValue.
      2. -
    -
    10. -
  10. Else initialValue is not present, -
      -
    1. Let kPresent be false.
      2. -
    2. Repeat, while kPresent is false and k ≥ 0 -
        -
      1. Let Pk be ToString(k).
        2. -
      2. Let kPresent be HasProperty(O, Pk).
        3. -
      3. ReturnIfAbrupt(kPresent).
        4. -
      4. If kPresent is true, then -
          -
        1. Let accumulator be Get(O, Pk).
          2. -
        2. ReturnIfAbrupt(accumulator).
          3. -
        -
        5. -
      5. Decrease k by 1.
        6. -
      -
      3. -
    3. If kPresent is false, throw a TypeError exception.
      4. -
    -
    11. -
  11. Repeat, while k ≥ 0 -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let accumulator be the result of calling the [[Call]] internal method of callbackfn with - undefined as thisArgument and a List - containing accumulator, kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(accumulator).
        5. -
      -
      5. -
    5. Decrease k by 1.
      6. -
    -
    12. -
  12. Return accumulator.
    13. -
- -

The length property of the reduceRight method is 1.

- -
-

NOTE The reduceRight function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the reduceRight function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.20 Array.prototype.reverse ( )

- -

NOTE The elements of the array are rearranged so as to - reverse their order. The object is returned as the result of the call.

- -

When the reverse method is called the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let middle be floor(len/2).
    7. -
  7. Let lower be 0.
    8. -
  8. Repeat, while lower ≠ middle -
      -
    1. Let upper be len− lower −1.
      2. -
    2. Let upperP be ToString(upper).
      3. -
    3. Let lowerP be ToString(lower).
      4. -
    4. Let lowerExists be HasProperty(O, lowerP).
      5. -
    5. ReturnIfAbrupt(lowerExists).
      6. -
    6. If lowerExists is true, then -
        -
      1. Let lowerValue be Get(O, lowerP).
        2. -
      2. ReturnIfAbrupt(lowerValue).
        3. -
      -
      7. -
    7. Let upperExists be HasProperty(O, upperP).
      8. -
    8. ReturnIfAbrupt(upperExists).
      9. -
    9. If upperExists is true, then -
        -
      1. Let upperValue be Get(O, upper).
        2. -
      2. ReturnIfAbrupt(upperValue).
        3. -
      -
      10. -
    10. If lowerExists is true and upperExists is true, then -
        -
      1. Let putStatus be Put(O, lowerP, upperValue, - true).
        2. -
      2. ReturnIfAbrupt(putStatus).
        3. -
      3. Let putStatus be Put(O, upperP, lowerValue, - true).
        4. -
      4. ReturnIfAbrupt(putStatus).
        5. -
      -
      11. -
    11. Else if lowerExists is false and upperExists is true, then -
        -
      1. Let putStatus be Put(O, lowerP, upperValue, - true).
        2. -
      2. ReturnIfAbrupt(putStatus).
        3. -
      3. Let deleteStatus be DeletePropertyOrThrow (O, - upperP).
        4. -
      4. ReturnIfAbrupt(deleteStatus).
        5. -
      -
      12. -
    12. Else if lowerExists is true and upperExists is false, then -
        -
      1. Let deleteStatus be DeletePropertyOrThrow (O, - lowerP).
        2. -
      2. ReturnIfAbrupt(deleteStatus).
        3. -
      3. Let putStatus be Put(O, upperP, lowerValue, - true).
        4. -
      4. ReturnIfAbrupt(putStatus).
        5. -
      -
      13. -
    13. Else both lowerExists and upperExists are false, -
        -
      1. No action is required.
        2. -
      -
      14. -
    14. Increase lower by 1.
      15. -
    -
    9. -
  9. Return O .
    10. -
- -
-

NOTE The reverse function is intentionally generic; it does not require that its - this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a method. - Whether the reverse function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.21 Array.prototype.shift ( )

- -

NOTE The first element of the array is removed from the - array and returned.

- -

When the shift method is called the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If len is zero, then -
      -
    1. Let putStatus be Put(O, "length", 0, - true).
      2. -
    2. ReturnIfAbrupt(putStatus).
      3. -
    3. Return undefined.
      4. -
    -
    7. -
  7. Let first be Get(O, "0").
    8. -
  8. ReturnIfAbrupt(first).
    9. -
  9. Let k be 1.
    10. -
  10. Repeat, while k < len -
      -
    1. Let from be ToString(k).
      2. -
    2. Let to be ToString(k–1).
      3. -
    3. Let fromPresent be HasProperty(O, from).
      4. -
    4. ReturnIfAbrupt(fromPresent).
      5. -
    5. If fromPresent is true, then -
        -
      1. Let fromVal be Get(O, from).
        2. -
      2. ReturnIfAbrupt(fromVal).
        3. -
      3. Let putStatus be Put(O, to, fromVal, - true).
        4. -
      4. ReturnIfAbrupt(putStatus).
        5. -
      -
      6. -
    6. Else fromPresent is false, -
        -
      1. Let deleteStatus be DeletePropertyOrThrow(O, - to).
        2. -
      2. ReturnIfAbrupt(deleteStatus).
        3. -
      -
      7. -
    7. Increase k by 1.
      8. -
    -
    11. -
  11. Let deleteStatus be DeletePropertyOrThrow(O, ToString(len–1)).
    12. -
  12. ReturnIfAbrupt(deleteStatus).
    13. -
  13. Let putStatus be Put(O, "length", len–1, - true).
    14. -
  14. ReturnIfAbrupt(putStatus).
    15. -
  15. Return first.
    16. -
- -
-

NOTE The shift function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the shift function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.22 Array.prototype.slice (start, end)

- -

NOTE The slice method takes two arguments, - start and end, and returns an array containing the elements of the array from element start up to, - but not including, element end (or through the end of the array if end is undefined). If start - is negative, it is treated as length+start where length is the length of the array. If end is - negative, it is treated as length+end where length is the length of the array.

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length").
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let relativeStart be ToInteger(start).
    7. -
  7. ReturnIfAbrupt(relativeStart).
    8. -
  8. If relativeStart is negative, let k be max((len + relativeStart),0); else let k - be min(relativeStart, len).
    9. -
  9. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
    10. -
  10. ReturnIfAbrupt(relativeEnd).
    11. -
  11. If relativeEnd is negative, let final be max((len + relativeEnd),0); else let - final be min(relativeEnd, len).
    12. -
  12. Let count be max(final – k, 0).
    13. -
  13. Let A be undefined.
    14. -
  14. If O is an exotic Array object, then -
      -
    1. Let C be Get(O, "constructor").
      2. -
    2. ReturnIfAbrupt(C).
      3. -
    3. If IsConstructor(C) is true, then -
        -
      1. Let thisRealm be the running execution context’s Realm.
        2. -
      2. If thisRealm and the value of C’s [[Realm]] internal slot are the same value, then -
          -
        1. Let A be the result of calling the [[Construct]] internal method of C with argument - (count).
          2. -
        -
        3. -
      -
      4. -
    -
    15. -
  15. If A is undefined, then -
      -
    1. Let A be ArrayCreate(count).
      2. -
    -
    16. -
  16. ReturnIfAbrupt(A).
    17. -
  17. Let n be 0.
    18. -
  18. Repeat, while k < final -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let status be CreateDataPropertyOrThrow(A, ToString(n), kValue ).
        4. -
      4. ReturnIfAbrupt(status).
        5. -
      -
      5. -
    5. Increase k by 1.
      6. -
    6. Increase n by 1.
      7. -
    -
    19. -
  19. Let putStatus be Put(A, "length", n, - true).
    20. -
  20. ReturnIfAbrupt(putStatus).
    21. -
  21. Return A.
    22. -
- -

The length property of the slice method is 2.

- -
-

NOTE 1 The explicit setting of the length property of the result Array in step - 19 is necessary to ensure that its value is correct in situations where the trailing elements of the result Array are - not present.

-
- -
-

NOTE 2 The slice function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the slice function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.23 Array.prototype.some ( callbackfn [ , thisArg ] )

- -

NOTE callbackfn should be a function that accepts - three arguments and returns a value that is coercible to the Boolean value true or false. some - calls callbackfn once for each element present in the array, in ascending order, until it finds one where - callbackfn returns true. If such an element is found, some immediately returns true. - Otherwise, some returns false. callbackfn is called only for elements of the array which - actually exist; it is not called for missing elements of the array.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the element, the index of the element, and - the object being traversed.

- -

some does not directly mutate the object on which it is called but the object may be mutated - by the calls to callbackfn.

- -

The range of elements processed by some is set before the first call to callbackfn. - Elements that are appended to the array after the call to some begins will not be visited by - callbackfn. If existing elements of the array are changed, their value as passed to callbackfn will be the - value at the time that some visits them; elements that are deleted after the call to some begins - and before being visited are not visited. some acts like the "exists" quantifier in mathematics. In - particular, for an empty array, it returns false.

- -

When the some method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenValue be Get(O, "length").
    4. -
  4. Let len be ToLength(lenValue).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    7. -
  7. If thisArg was supplied, let T be thisArg; else let T be undefined.
    8. -
  8. Let k be 0.
    9. -
  9. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kPresent be HasProperty(O, Pk).
      3. -
    3. ReturnIfAbrupt(kPresent).
      4. -
    4. If kPresent is true, then -
        -
      1. Let kValue be Get(O, Pk).
        2. -
      2. ReturnIfAbrupt(kValue).
        3. -
      3. Let testResult be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - kValue, k, and O as argumentsList.
        4. -
      4. ReturnIfAbrupt(testResult).
        5. -
      5. If ToBoolean(testResult) is true, return true.
        6. -
      -
      5. -
    5. Increase k by 1.
      6. -
    -
    10. -
  10. Return false.
    11. -
- -

The length property of the some method is 1.

- -
-

NOTE The some function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the some function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-
-

22.1.3.24 Array.prototype.sort (comparefn)

- -

The elements of this array are sorted. The sort is not necessarily stable (that is, elements that compare equal do - not necessarily remain in their original order). If comparefn is not undefined, it should be a - function that accepts two arguments x and y and returns a negative value if x < y, zero if x = y, or a positive value if x > - y.

- -

Upon entry, the following steps are performed to initialize evaluation of the sort function:

- -
    -
  1. Let obj be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. Let lenValue be Get(obj, "length").
    3. -
  3. Let len be ToLength(lenValue).
    4. -
  4. ReturnIfAbrupt(len).
    5. -
- -

The result of the sort function is then determined as follows:

- -

If comparefn is not undefined and is not a consistent comparison function for the elements of this - array (see below), the behaviour of sort is implementation-defined.

- -

Let proto be the result of calling the [[GetPrototypeOf]] internal method of obj. If - proto is not null and there exists an integer j such that all of the conditions below are - satisfied then the behaviour of sort is implementation-defined:

- - - -

The behaviour of sort is also implementation defined if obj is sparse and any of the - following conditions are true:

- -
    -
  • -

    The result of the predicate IsExtensible(obj) is false.

    -
    • - -
  • -

    Any array index property of obj whose name is a nonnegative integer less than len is a data - property whose [[Configurable]] attribute is false.

    -
    • -
- -

The behaviour of sort is also implementation defined if any array index property of obj whose - name is a nonnegative integer less than len is an accessor property or is a data property whose [[Writable]] - attribute is false.

- -

Otherwise, the following steps are taken:

- -
    -
  1. Perform an implementation-dependent sequence of calls to the [[Get]] and [[Set]] internal methods of obj, - to the DeletePropertyOrThrow abstract operation with obj as the - first argument, and to SortCompare (described below), where the property key argument for each call to [[Get]], [[Set]], or DeletePropertyOrThrow is the string representation of a nonnegative integer - less than len and where the arguments for calls to SortCompare are results - of previous calls to the [[Get]] internal method. If obj is not sparse then DeletePropertyOrThrow must not be called. If any [[Set]] call returns - false a TypeError exception is thrown. If an abrupt completion is returned from any of these operations, - it is immediately returned as the value of this function.
    2. -
  2. Return obj.
    3. -
- -

The returned object must have the following two characteristics:

- -
    -
  • -

    There must be some mathematical permutation π of the - nonnegative integers less than len, such that for every nonnegative integer j less than - len, if property old[j] existed, then new[π(j)] is exactly the same value as old[j],. But if property old[j] did not exist, then new[π(j)] does not exist.

    -
    • - -
  • -

    Then for all nonnegative integers j and k, each less than len, if SortCompare(j,k) < 0 - (see SortCompare below), then π(j) < π(k).

    -
    • -
- -

Here the notation old[j] is used to refer to the - hypothetical result of calling the [[Get]] internal method of obj with argument j before this - function is executed, and the notation new[j] to refer to the - hypothetical result of calling the [[Get]] internal method of obj with argument j after this - function has been executed.

- -

A function comparefn is a consistent comparison function for a set of values S if all of the - requirements below are met for all values a, b, and c (possibly the same value) in the - set S: The notation a <CF b means comparefn(a,b) < 0; a =CF b means comparefn(a,b) = 0 (of either sign); and a >CF b means comparefn(a,b) > 0.

- -
    -
  • -

    Calling comparefn(a,b) always returns the same value v when given a specific pair of - values a and b as its two arguments. Furthermore, Type(v) is Number, and v is not NaN. Note that this - implies that exactly one of a <CF b, - a =CF b, and a >CF b will be true for a - given pair of a and b.

    -
    • - -
  • -

    Calling comparefn(a,b) does not modify obj.

    -
    • - -
  • -

    a =CF a (reflexivity)

    -
    • - -
  • -

    If a =CF b, then b =CF a (symmetry)

    -
    • - -
  • -

    If a =CF b and b =CF c, then - a =CF c (transitivity of =CF)

    -
    • - -
  • -

    If a <CF b and b <CF c, then - a <CF c (transitivity of <CF)

    -
    • - -
  • -

    If a >CF b and b >CF c, then - a >CF c (transitivity of >CF)

    -
    • -
- -
-

NOTE 1 The above conditions are necessary and sufficient to ensure that comparefn - divides the set S into equivalence classes and that these equivalence classes are totally ordered.

-
- -
-

NOTE 2 The sort function is intentionally generic; it does not require that - its this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a - method. Whether the sort function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.24.1 Runtime Semantics: SortCompare Abstract Operation

- -

When the SortCompare abstract operation is called with two arguments j and k, the following - steps are taken:

- -
    -
  1. Let jString be ToString(j).
    2. -
  2. Let kString be ToString(k).
    3. -
  3. Let hasj be HasProperty(obj, jString).
    4. -
  4. ReturnIfAbrupt(hasj).
    5. -
  5. Let hask be HasProperty(obj, kString).
    6. -
  6. ReturnIfAbrupt(hask).
    7. -
  7. If hasj and hask are both false, then return +0.
    8. -
  8. If hasj is false, then return 1.
    9. -
  9. If hask is false, then return –1.
    10. -
  10. Let x be Get(obj,jString).
    11. -
  11. ReturnIfAbrupt(x).
    12. -
  12. Let y be Get(obj, kString).
    13. -
  13. ReturnIfAbrupt(y).
    14. -
  14. If x and y are both undefined, return +0.
    15. -
  15. If x is undefined, return 1.
    16. -
  16. If y is undefined, return −1.
    17. -
  17. If the argument comparefn is not undefined, then -
      -
    1. If IsCallable(comparefn) is false, throw a TypeError - exception.
      2. -
    2. Return the result of calling the [[Call]] internal method of comparefn passing undefined as - thisArgument and with a List containing the - values of x and y as the argumentsList.
      3. -
    -
    18. -
  18. Let xString be ToString(x).
    19. -
  19. ReturnIfAbrupt(xString).
    20. -
  20. Let yString be ToString(y).
    21. -
  21. ReturnIfAbrupt(yString).
    22. -
  22. If xString < yString, return −1.
    23. -
  23. If xString > yString, return 1.
    24. -
  24. Return +0.
    25. -
- -
-

NOTE Because non-existent property values always compare greater than undefined - property values, and undefined always compares greater than any other value, undefined property values - always sort to the end of the result, followed by non-existent property values.

-
-
-
- -
-

22.1.3.25 Array.prototype.splice (start, deleteCount , ...items )

- -

NOTE When the splice method is called with - two or more arguments start, deleteCount and zero or more items,., the deleteCount elements of - the array starting at integer index start are replaced by the arguments items,. An Array object containing - the deleted elements (if any) is returned.

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length")
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let relativeStart be ToInteger(start).
    7. -
  7. ReturnIfAbrupt(relativeStart).
    8. -
  8. If relativeStart is negative, let actualStart be max((len + relativeStart),0); else let - actualStart be min(relativeStart, len).
    9. -
  9. If the number of actual arguments is 0, then -
      -
    1. Let actualDeleteCount be 0.
      2. -
    -
    10. -
  10. Else if the number of actual arguments is 1, then -
      -
    1. Let actualDeleteCount be len - actualStart
      2. -
    -
    11. -
  11. Else, -
      -
    1. Let dc be ToInteger(deleteCount).
      2. -
    2. ReturnIfAbrupt(dc).
      3. -
    3. Let actualDeleteCount be min(max(dc,0), len – actualStart).
      4. -
    -
    12. -
  12. Let A be undefined.
    13. -
  13. If O is an exotic Array object, then -
      -
    1. Let C be Get(O, "constructor").
      2. -
    2. ReturnIfAbrupt(C).
      3. -
    3. If IsConstructor(C) is true, then -
        -
      1. Let thisRealm be the running execution context’s Realm.
        2. -
      2. If thisRealm and the value of C’s [[Realm]] internal slot are the same value, then -
          -
        1. Let A be the result of calling the [[Construct]] internal method of C with argument - (actualDeleteCount).
          2. -
        -
        3. -
      -
      4. -
    -
    14. -
  14. If A is undefined, then -
      -
    1. Let A be ArrayCreate(actualDeleteCount).
      2. -
    -
    15. -
  15. ReturnIfAbrupt(A).
    16. -
  16. Let k be 0.
    17. -
  17. Repeat, while k < actualDeleteCount -
      -
    1. Let from be ToString(actualStart+k).
      2. -
    2. Let fromPresent be HasProperty(O, from).
      3. -
    3. ReturnIfAbrupt(fromPresent).
      4. -
    4. If fromPresent is true, then -
        -
      1. Let fromValue be Get(O, from).
        2. -
      2. ReturnIfAbrupt(fromValue).
        3. -
      3. Let status be CreateDataPropertyOrThrow(A, ToString(k), fromValue).
        4. -
      4. ReturnIfAbrupt(status).
        5. -
      -
      5. -
    5. Increment k by 1.
      6. -
    -
    18. -
  18. Let putStatus be Put(A, "length", - actualDeleteCount, true).
    19. -
  19. ReturnIfAbrupt(putStatus).
    20. -
  20. Let items be a List whose elements are, in left to - right order, the portion of the actual argument list starting with the third argument. The list will be empty fewer - than three arguments were passed.
    21. -
  21. Let itemCount be the number of elements in items.
    22. -
  22. If itemCount < actualDeleteCount, then -
      -
    1. Let k be actualStart.
      2. -
    2. Repeat, while k < (len – actualDeleteCount) -
        -
      1. Let from be ToString(k+actualDeleteCount).
        2. -
      2. Let to be ToString(k+itemCount).
        3. -
      3. Let fromPresent be HasProperty(O, from).
        4. -
      4. ReturnIfAbrupt(fromPresent).
        5. -
      5. If fromPresent is true, then -
          -
        1. Let fromValue be Get(O, from).
          2. -
        2. ReturnIfAbrupt(fromValue).
          3. -
        3. Let putStatus be Put(O, to, fromValue, - true).
          4. -
        4. ReturnIfAbrupt(putStatus).
          5. -
        -
        6. -
      6. Else fromPresent is false, -
          -
        1. Let deleteStatus be DeletePropertyOrThrow(O, - to).
          2. -
        2. ReturnIfAbrupt(deleteStatus).
          3. -
        -
        7. -
      7. Increase k by 1.
        8. -
      -
      3. -
    3. Let k be len.
      4. -
    4. Repeat, while k > (len – actualDeleteCount + itemCount) -
        -
      1. Let deleteStatus be DeletePropertyOrThrow(O, ToString(k–1)).
        2. -
      2. ReturnIfAbrupt(deleteStatus).
        3. -
      3. Decrease k by 1.
        4. -
      -
      5. -
    -
    23. -
  23. Else if itemCount > actualDeleteCount, then -
      -
    1. Let k be (len – actualDeleteCount).
      2. -
    2. Repeat, while k > actualStart -
        -
      1. Let from be ToString(k + actualDeleteCount – 1).
        2. -
      2. Let to be ToString(k + itemCount – 1)
        3. -
      3. Let fromPresent be HasProperty(O, from).
        4. -
      4. ReturnIfAbrupt(fromPresent).
        5. -
      5. If fromPresent is true, then -
          -
        1. Let fromValue be Get(O, from).
          2. -
        2. ReturnIfAbrupt(fromValue).
          3. -
        3. Let putStatus be Put(O, to, fromValue, - true).
          4. -
        4. ReturnIfAbrupt(putStatus).
          5. -
        -
        6. -
      6. Else fromPresent is false, -
          -
        1. Let deleteStatus be DeletePropertyOrThrow(O, - to).
          2. -
        2. ReturnIfAbrupt(deleteStatus).
          3. -
        -
        7. -
      7. Decrease k by 1.
        8. -
      -
      3. -
    -
    24. -
  24. Let k be actualStart.
    25. -
  25. Repeat, while items is not empty -
      -
    1. Remove the first element from items and let E be the value of that element.
      2. -
    2. Let putStatus be Put(O, ToString(k), E, true).
      3. -
    3. ReturnIfAbrupt(putStatus).
      4. -
    4. Increase k by 1.
      5. -
    -
    26. -
  26. Let putStatus be Put(O, "length", len – - actualDeleteCount + itemCount, true).
    27. -
  27. ReturnIfAbrupt(putStatus).
    28. -
  28. Return A.
    29. -
- -

The length property of the splice method is 2.

- -
-

NOTE 1 The explicit setting of the length property of the result Array in step - 18 is necessary to ensure that its value is correct in situations where its trailing elements are not present.

-
- -
-

NOTE 2 The splice function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the splice function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.26 Array.prototype.toLocaleString ( )

- -

NOTE The elements of the array are converted to Strings - using their toLocaleString methods, and these Strings are then concatenated, separated by occurrences of a - separator String that has been derived in an implementation-defined locale-specific way. The result of calling this - function is intended to be analogous to the result of toString, except that the result of this function is - intended to be locale-specific.

- -

The following steps are taken:

- -
    -
  1. Let array be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(array).
    3. -
  3. Let arrayLen be Get(array, "length").
    4. -
  4. Let len be ToLength(arrayLen).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let separator be the String value for the list-separator String appropriate for the host environment’s - current locale (this is derived in an implementation-defined way).
    7. -
  7. If len is zero, return the empty String.
    8. -
  8. Let firstElement be Get(array, "0").
    9. -
  9. ReturnIfAbrupt(firstElement).
    10. -
  10. If firstElement is undefined or null, then -
      -
    1. Let R be the empty String.
      2. -
    -
    11. -
  11. Else -
      -
    1. Let R be Invoke(firstElement, "toLocaleString").
      2. -
    2. Let R be ToString(R).
      3. -
    3. ReturnIfAbrupt(R).
      4. -
    -
    12. -
  12. Let k be 1.
    13. -
  13. Repeat, while k < len -
      -
    1. Let S be a String value produced by concatenating R and separator.
      2. -
    2. Let nextElement be Get(array, ToString(k)).
      3. -
    3. ReturnIfAbrupt(nextElement).
      4. -
    4. If nextElement is undefined or null, then -
        -
      1. Let R be the empty String.
        2. -
      -
      5. -
    5. Else -
        -
      1. Let R be Invoke(nextElement, "toLocaleString").
        2. -
      2. Let R be ToString(R).
        3. -
      3. ReturnIfAbrupt(R).
        4. -
      -
      6. -
    6. Let R be a String value produced by concatenating S and R.
      7. -
    7. Increase k by 1.
      8. -
    -
    14. -
  14. Return R.
    15. -
- -
-

NOTE 1 The first parameter to this function is likely to be used in a future version of this - standard; it is recommended that implementations do not use this parameter position for anything else.

-
- -
-

NOTE 2 The toLocaleString function is intentionally generic; it does not require - that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a - method. Whether the toLocaleString function can be applied successfully to an exotic object that is not an - Array is implementation-dependent.

-
-
- -
-

22.1.3.27 Array.prototype.toString ( )

- -

When the toString method is called, the following steps are taken:

- -
    -
  1. Let array be the result of calling ToObject on the this value.
    2. -
  2. ReturnIfAbrupt(array).
    3. -
  3. Let func be Get(array, "join").
    4. -
  4. ReturnIfAbrupt(func).
    5. -
  5. If IsCallable(func) is false, then let func be the intrinsic - function %ObjProto_toString% (19.1.3.6).
    6. -
  6. Return the result of calling the [[Call]] internal method of func providing array as - thisArgument and an empty List as - argumentsList.
    7. -
- -
-

NOTE The toString function is intentionally generic; it does not require that - its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the toString function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.28 Array.prototype.unshift ( ...items )

- -

NOTE The arguments are prepended to the start of the - array, such that their order within the array is the same as the order in which they appear in the argument list.

- -

When the unshift method is called with zero or more arguments item1, item2, etc., - the following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let lenVal be Get(O, "length")
    4. -
  4. Let len be ToLength(lenVal).
    5. -
  5. ReturnIfAbrupt(len).
    6. -
  6. Let argCount be the number of actual arguments.
    7. -
  7. If argCount > 0, then -
      -
    1. Let k be len.
      2. -
    2. Repeat, while k > 0, -
        -
      1. Let from be ToString(k–1).
        2. -
      2. Let to be ToString(k+argCount –1).
        3. -
      3. Let fromPresent be HasProperty(O, from).
        4. -
      4. ReturnIfAbrupt(fromPresent).
        5. -
      5. If fromPresent is true, then -
          -
        1. Let fromValue be the result of Get(O, from).
          2. -
        2. ReturnIfAbrupt(fromValue).
          3. -
        3. Let putStatus be Put(O, to, fromValue, - true).
          4. -
        4. ReturnIfAbrupt(putStatus).
          5. -
        -
        6. -
      6. Else fromPresent is false, -
          -
        1. Let deleteStatus be DeletePropertyOrThrow(O, - to).
          2. -
        2. ReturnIfAbrupt(deleteStatus).
          3. -
        -
        7. -
      7. Decrease k by 1.
        8. -
      -
      3. -
    3. Let j be 0.
      4. -
    4. Let items be a List whose elements are, in left to - right order, the arguments that were passed to this function invocation.
      5. -
    5. Repeat, while items is not empty -
        -
      1. Remove the first element from items and let E be the value of that element.
        2. -
      2. Let putStatus be Put(O, ToString(j), E, true).
        3. -
      3. ReturnIfAbrupt(putStatus).
        4. -
      4. Increase j by 1.
        5. -
      -
      6. -
    -
    8. -
  8. Let putStatus be Put(O, "length", - len+argCount, true).
    9. -
  9. ReturnIfAbrupt(putStatus).
    10. -
  10. Return len+argCount.
    11. -
- -

The length property of the unshift method is 1.

- -
-

NOTE The unshift function is intentionally generic; it does not require that its - this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. - Whether the unshift function can be applied successfully to an exotic object that is not an Array is - implementation-dependent.

-
-
- -
-

22.1.3.29 Array.prototype.values ( )

- -

The following steps are taken:

- -
    -
  1. Let O be the result of calling ToObject with the this value as its - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Return the result of calling the CreateArrayIterator abstract operation with - arguments O and "value".
    4. -
- -

This function is the %ArrayProto_values% intrinsic object.

-
- -
-

22.1.3.30 Array.prototype [ @@iterator ] ( )

- -

The initial value of the @@iterator property is the same function object as the initial value of the Array.prototype.values property.

-
- -
-

22.1.3.31 Array.prototype [ @@unscopables ]

- -

The initial value of the @@unscopables data property is an object created by the following steps:

- -
    -
  1. Let blackList be ArrayCreate(7, %ArrayPrototype%).
    2. -
  2. Perform CreateDataProperty(blackList, "0", - "find").
    3. -
  3. Perform CreateDataProperty(blackList, "1", - "findIndex").
    4. -
  4. Perform CreateDataProperty(blackList, "2", - "fill").
    5. -
  5. Perform CreateDataProperty(blackList, "3", - "copyWithin").
    6. -
  6. Perform CreateDataProperty(blackList, "4", - "entries").
    7. -
  7. Perform CreateDataProperty(blackList, "5", - "keys").
    8. -
  8. Perform CreateDataProperty(blackList, "6", - "values").
    9. -
  9. Assert: Each of the above calls will return true.
    10. -
  10. Return blackList.
    11. -
- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, - [[Configurable]]: true }.

- -
-

NOTE The elements of this array are property names that were not included as standard - properties of Array.prototype prior to the sixth edition of this specification. These names are ignored for - with statement binding purposes in order to preserve the behaviour of existing code that might use one of - these names as a binding in an outer scope that is shadowed by a with statement whose binding object is an - Array object.

-
-
-
- -
-
-

22.1.4 Properties of Array Instances

- -

Array instances are exotic Array objects and have the internal methods specified for such objects. Array instances - inherit properties from the Array prototype object. Array instances also have an [[ArrayInitializationState]] internal slot.

- -

Array instances have a length property, and a set of enumerable properties with array index names.

-
- -
-

22.1.4.1 length

- -

The length property of this Array object is a data property whose value is always numerically greater than - the name of every deletable property whose name is an array index.

- -

The length property initially has the attributes { - [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.

- -
-

NOTE Attempting to set the length property of an Array object to a value that is numerically - less than or equal to the largest numeric property name of an existing array indexed non-deletable property of the array - will result in the length being set to a numeric value that is one greater than that largest numeric property name. See - 9.4.2.1.

-
-
-
- -
-
-

22.1.5 Array Iterator Objects

- -

An Array Iterator is an object, that represents a specific iteration over some specific Array instance object. There is - not a named constructor for Array Iterator objects. Instead, Array iterator objects are created by calling certain methods - of Array instance objects.

-
- -
-

22.1.5.1 CreateArrayIterator Abstract Operation

- -

Several methods of Array objects return Iterator objects. The abstract operation CreateArrayIterator with arguments - array and kind is used to create such iterator objects. It performs the following steps:

- -
    -
  1. Let O be ToObject(array).
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Let iterator be ObjectCreate(%ArrayIteratorPrototype%, ([[IteratedObject]], - [[ArrayIteratorNextIndex]], [[ArrayIterationKind]])).
    4. -
  4. Set iterator’s [[IteratedObject]] internal - slot to O.
    5. -
  5. Set iterator’s [[ArrayIteratorNextIndex]] internal slot to 0.
    6. -
  6. Set iterator’s [[ArrayIterationKind]] internal slot to kind.
    7. -
  7. Return iterator.
    8. -
-
- -
-
-

22.1.5.2 The %ArrayIteratorPrototype% Object

- -

All Array Iterator Objects inherit properties from the %ArrayIteratorPrototype% intrinsic object. The - %ArrayIteratorPrototype% object is an ordinary object and its [[Prototype]] internal slot is the %ObjectPrototype% intrinsic object. In - addition, %ArrayIteratorPrototype% has the following properties:

-
- -
-

22.1.5.2.1 %ArrayIteratorPrototype%. next( )

-
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have all of the internal slots of an Array Iterator Instance (22.1.5.3), throw a TypeError exception.
    4. -
  4. Let a be the value of the [[IteratedObject]] internal slot of O.
    5. -
  5. If a is undefined, then return CreateIterResultObject(undefined, true).
    6. -
  6. Let index be the value of the [[ArrayIteratorNextIndex]] internal slot of O.
    7. -
  7. Let itemKind be the value of the [[ArrayIterationKind]] internal slot of O.
    8. -
  8. Let lenValue be Get(a, "length").
    9. -
  9. Let len be ToLength(lenValue).
    10. -
  10. ReturnIfAbrupt(len).
    11. -
  11. If index ≥ len, then -
      -
    1. Set the value of the [[IteratedObject]] internal - slot of O to undefined.
      2. -
    2. Return CreateIterResultObject(undefined, true).
      3. -
    -
    12. -
  12. Set the value of the [[ArrayIteratorNextIndex]] internal - slot of O to index+1.
    13. -
  13. If itemKind is "key", then let result be index.
    14. -
  14. Else, -
      -
    1. Let elementKey be ToString(index).
      2. -
    2. Let elementValue be Get(a, elementKey).
      3. -
    3. ReturnIfAbrupt(elementValue).
      4. -
    -
    15. -
  15. If itemKind is "value", then let result be elementValue.
    16. -
  16. Else, -
      -
    1. Assert itemKind is "key+value",.
      2. -
    2. Let result be ArrayCreate(2).
      3. -
    3. Assert: result is a new, well-formed Array object so the - following operations will never fail.
      4. -
    4. Call CreateDataProperty(result, "0", - index).
      5. -
    5. Call CreateDataProperty(result, "1", - elementValue).
      6. -
    -
    17. -
  17. Return CreateIterResultObject(result, false).
    18. -
-
- -
-

22.1.5.2.2 %ArrayIteratorPrototype% [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

22.1.5.2.3 %ArrayIteratorPrototype% [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Array Iterator".

-
-
- -
-

22.1.5.3 Properties of Array Iterator Instances

- -

Array Iterator instances are ordinary objects that inherit properties from the %ArrayIteratorPrototype% intrinsic - object. Array Iterator instances are initially created with the internal slots listed in Table - 43.

- -
-
Table 43 — Internal Slots of Array Iterator Instances
- - - - - - - - - - - - - - - - - -
Internal SlotDescription
[[IteratedObject]]The object whose array elements are being iterated.
[[ArrayIteratorNextIndex]]The integer index of the next array index to be examined by this iteration.
[[ArrayIterationKind]]A string value that identifies what is to be returned for each element of the iteration. The possible values are: "key", "value", "key+value".
-
-
-
-
- -
-
-

22.2 - TypedArray Objects

- -

TypedArray objects present an array-like view of an underlying binary data buffer (24.1). Each element of a TypedArray instance has the same underlying binary - scalar data type. There is a distinct TypedArray constructor, listed in Table 44, for each of - the nine supported element types. Each constructor in Table 44 has a corresponding distinct - prototype object.

- -
-
Table 44 – The TypedArray Constructors
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Constructor NameElement
Type		Element SizeConversion OperationDescriptionEquivalent C Type
Int8ArrayInt81ToInt88-bit 2’s complement signed integersigned char
Uint8ArrayUint81ToUint88-bit unsigned integerunsigned char
Uint8ClampedArrayUint8C1ToUint8Clamp8-bit unsigned integer (clamped conversion)unsigned char
Int16ArrayInt162ToInt1616-bit 2’s complement signed integerShort
Uint16ArrayUint162ToUint1616-bit unsigned integerunsigned short
Int32ArrayInt324ToInt3232-bit 2’s complement signed integerInt
Uint32ArrayUint324ToUint3232-bit unsigned integerunsigned int
Float32ArrayFloat32432-bit IEEE floating pointFloat
Float64ArrayFloat64864-bit IEEE floating pointDouble
-
- -

In the definitions below, references to TypedArray should be replaced with the appropriate constructor name from - the above table. The phrase “the element size in bytes” refers to the value in the Element Size column of the - table in the row corresponding to the constructor. The phrase “element Type” refers to the value in the Element - Type column for that row.

-
- -
-
-

22.2.1 The %TypedArray% Intrinsic Object

- -

The %TypedArray% intrinsic object is a constructor-like function object that all of the TypedArray constructor - object inherit from. %TypedArray% and its corresponding prototype object provide common properties that are inherited by - all TypedArray constructors and their instances. The %TypedArray% intrinsic does not have a global name or appear - as a property of the global object.

- -

If the this value passed in the call is an Object with a [[ViewedArrayBuffer]] internal slot whose value is undefined, it initializes the this value using the argument values. This permits super - invocation of the TypedArray constructors by TypedArray subclasses.

- -

The %TypedArray% intrinsic function object is designed to act as the superclass of the various TypedArray - constructors. Those constructors use %TypedArray% to initialize their instances by invoking %TypedArray% as if by making a - super call. The %TypedArray% intrinsic function is not designed to be directly called in any other way. If - %TypedArray% is directly called or called as part of a new expression an exception is thrown.

- -

The actual behaviour of a super call of %TypedArray% depends upon the number and kind of arguments that - are passed to it.

-
- -
-

22.2.1.1 %TypedArray% ( length )

- -

This description applies if and only when %TypedArray% function is called and the Type of the first argument is not - Object.

- -

%TypedArray% called with argument length performs the following steps:

- -
    -
  1. Assert: Type(length) is not Object.
    2. -
  2. Let O be the this value.
    3. -
  3. If Type(O) is not Object, then throw a TypeError - exception.
    4. -
  4. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    5. -
  5. If the value of O’s [[TypedArrayName]] internal slot is undefined, then throw a - TypeError exception.
    6. -
  6. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    7. -
  7. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    8. -
  8. Let constructorName be the string value of O’s [[TypedArrayName]] internal slot.
    9. -
  9. Let elementType be the string value of the Element Type value in Table 44 for - constructorName.
    10. -
  10. Let numberLength be ToNumber(length).
    11. -
  11. Let elementLength be ToLength(numberLength).
    12. -
  12. ReturnIfAbrupt(elementLength).
    13. -
  13. If SameValueZero(numberLength, elementLength) is false, then - throw a RangeError exception.
    14. -
  14. Let data be AllocateArrayBuffer(%ArrayBuffer%).
    15. -
  15. ReturnIfAbrupt(data).
    16. -
  16. Let elementSize be the Element Size value in Table 44 for - constructorName.
    17. -
  17. Let byteLength be elementSize × elementLength.
    18. -
  18. Let status be SetArrayBufferData(data, byteLength).
    19. -
  19. ReturnIfAbrupt(status).
    20. -
  20. Set O’s [[ViewedArrayBuffer]] internal - slot to data.
    21. -
  21. Set O’s [[ByteLength]] internal slot to - byteLength.
    22. -
  22. Set O’s [[ByteOffset]] internal slot to - 0.
    23. -
  23. Set O’s [[ArrayLength]] internal slot to - elementLength.
    24. -
  24. Return O.
    25. -
-
- -
-

22.2.1.2 %TypedArray% ( typedArray )

- -

This description applies if and only if the %TypedArray% function is called with at least one argument and the Type of - the first argument is Object and that object has a [[TypedArrayName]] internal slot.

- -

%TypedArray%called with argument typedArray performs the following steps:

- -
    -
  1. Assert: Type(typedArray) is Object and typedArray has a - [[TypedArrayName]] internal slot.
    2. -
  2. Let srcArray be typedArray.
    3. -
  3. Let O be the this value.
    4. -
  4. If Type(O) is not Object or if O does not have a - [[TypedArrayName]] internal slot, then throw a - TypeError exception.
    5. -
  5. If the value of O’s [[TypedArrayName]] internal slot is undefined, then throw a - TypeError exception.
    6. -
  6. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    7. -
  7. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    8. -
  8. If the value of srcArray’s [[ViewedArrayBuffer]] internal slot is undefined, then throw a - TypeError exception.
    9. -
  9. Let constructorName be the string value of O’s [[TypedArrayName]] internal slot.
    10. -
  10. Let elementType be the string value of the Element Type value in Table 44 for - constructorName.
    11. -
  11. Let elementLength be the value of srcArray’s [[ArrayLength]] internal slot.
    12. -
  12. Let srcName be the string value of srcArray’s [[TypedArrayName]] internal slot.
    13. -
  13. Let srcType be the string value of the Element Type value in Table 44 for - srcName.
    14. -
  14. Let srcElementSize be the Element Size value in Table 44 for srcName.
    15. -
  15. Let srcData be the value of srcArray’s [[ViewedArrayBuffer]] internal slot.
    16. -
  16. Let srcByteOffset be the value of srcArray’s [[ByteOffset]] internal slot.
    17. -
  17. Let elementSize be the Element Size value in Table 44 for - constructorName.
    18. -
  18. Let byteLength be elementSize × elementLength.
    19. -
  19. If SameValue(elementType,srcType), then -
      -
    1. Let data be CloneArrayBuffer(srcData, - srcByteOffset).
      2. -
    2. ReturnIfAbrupt(data).
      3. -
    -
    20. -
  20. Else, -
      -
    1. Let bufferConstructor be Get(srcData, "constructor").
      2. -
    2. ReturnIfAbrupt(bufferConstructor).
      3. -
    3. If bufferConstructor is undefined, then let bufferConstructor be %ArrayBuffer%.
      4. -
    4. Let data be AllocateArrayBuffer(bufferConstructor).
      5. -
    5. Let status be SetArrayBufferData(data, - byteLength).
      6. -
    6. ReturnIfAbrupt(status).
      7. -
    7. Let srcByteIndex be srcByteOffset.
      8. -
    8. Let targetByteIndex be 0.
      9. -
    9. Let count be elementLength.
      10. -
    10. Repeat, while count >0 -
        -
      1. Let value be GetValueFromBuffer (srcData, - srcByteIndex, srcType).
        2. -
      2. Let status be SetValueInBuffer(data, - targetByteIndex, elementType, value).
        3. -
      3. Set srcByteIndex to srcByteIndex + srcElementSize.
        4. -
      4. Set targetByteIndex to targetByteIndex + elementSize.
        5. -
      5. Decrement count by 1.
        6. -
      -
      11. -
    -
    21. -
  21. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    22. -
  22. Assert: O has not been reentrantly initialized.
    23. -
  23. Set O’s [[ViewedArrayBuffer]] internal - slot to data.
    24. -
  24. Set O’s [[ByteLength]] internal slot to - byteLength.
    25. -
  25. Set O’s [[ByteOffset]] internal slot to - 0.
    26. -
  26. Set O’s [[ArrayLength]] internal slot to - elementLength.
    27. -
  27. Return O.
    28. -
-
- -
-

22.2.1.3 %TypedArray% ( object )

- -

This description applies when the %TypedArray% function is called with at least one argument and the Type of first - argument is Object and that object does not have either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.

- -

%TypedArray% called with argument object performs the following steps:

- -
    -
  1. Assert: Type(object) is Object and object does not have - either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.
    2. -
  2. Let O be the this value.
    3. -
  3. If Type(O) is not Object or if O does not have a - [[TypedArrayName]] internal slot, then throw a - TypeError exception.
    4. -
  4. If the value of O’s [[TypedArrayName]] internal slot is undefined, then throw a - TypeError exception.
    5. -
  5. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    6. -
  6. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    7. -
  7. Return TypedArrayFrom(undefined, O, items, undefined, - undefined).
    8. -
-
- -
-

22.2.1.4 %TypedArray% ( buffer [ , byteOffset [ , length ] ] )

- -

This description applies when the %TypedArray% function is called with at least one argument and the Type of the first - argument is Object and that object has an [[ArrayBufferData]] internal slot.

- -

%TypedArray% called with arguments buffer, byteOffset, and - length performs the following steps:

- -
    -
  1. Assert: Type(buffer) is Object and buffer has an - [[ArrayBufferData]] internal slot.
    2. -
  2. Let O be the this value.
    3. -
  3. If the value of buffer’s [[ArrayBufferData]] internal slot is undefined, then throw a - TypeError exception.
    4. -
  4. If Type(O) is not Object or if O does not have a - [[TypedArrayName]] internal slot, then throw a - TypeError exception.
    5. -
  5. If the value of O’s [[TypedArrayName]] internal slot is undefined, then throw a - TypeError exception.
    6. -
  6. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    7. -
  7. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    8. -
  8. Let constructorName be the string value of O’s [[TypedArrayName]] internal slot.
    9. -
  9. Let elementType be the string value of the Element Type value in Table 44 for - constructorName.
    10. -
  10. Let elementSize be the Number value of the Element Size value in Table 44 for - constructorName.
    11. -
  11. Let offset be ToInteger(byteOffset).
    12. -
  12. ReturnIfAbrupt(offset).
    13. -
  13. If offset < 0, then throw a RangeError exception.
    14. -
  14. If offset modulo elementSize ≠ 0, then throw a - RangeError exception.
    15. -
  15. Let bufferByteLength be the value of buffer’s [[ArrayBufferByteLength]] internal slot.
    16. -
  16. If length is undefined, then -
      -
    1. If bufferByteLength modulo elementSize ≠ 0, then throw - a RangeError exception.
      2. -
    2. Let newByteLength be bufferByteLength – offset.
      3. -
    3. If newByteLength < 0, then throw a RangeError exception.
      4. -
    -
    17. -
  17. Else, -
      -
    1. Let newLength be ToLength(length).
      2. -
    2. ReturnIfAbrupt(newLength).
      3. -
    3. Let newByteLength be newLength × elementSize.
      4. -
    4. If offset+newByteLength > bufferByteLength, then throw a RangeError - exception.
      5. -
    -
    18. -
  18. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
    19. -
  19. Set O’s [[ViewedArrayBuffer]] internal - slot to buffer.
    20. -
  20. Set O’s [[ByteLength]] internal slot to - newByteLength.
    21. -
  21. Set O’s [[ByteOffset]] internal slot to - offset.
    22. -
  22. Set O’s [[ArrayLength]] internal slot to - newByteLength / elementSize .
    23. -
  23. Return O.
    24. -
-
- -
-

22.2.1.5 %TypedArray% ( all other argument combinations )

- -

If the %TypedArray% function is called with arguments that do not match any of the preceeding argument descriptions a - TypeError exception is thrown.

-
-
- -
-
-

22.2.2 Properties of the %TypedArray% Intrinsic Object

- -

The %TypedArray% intrinsic object is a built-in function object. The value of the [[Prototype]] internal slot of %TypedArray% is the Function prototype object - (19.2.3).

- -

Besides a length property whose value is 3 and a name property whose value is - "TypedArray", %TypedArray% has the following properties:

-
- -
-
-

22.2.2.1 %TypedArray%.from ( source [ , mapfn [ , thisArg ] ] )

- -

When the from method is called with argument source, and optional arguments mapfn and - thisArg, the following steps are taken:

- -
    -
  1. Let C be the this value.
    2. -
  2. If IsConstructor(C) is false, then throw a TypeError - exception.
    3. -
  3. Let items be ToObject(source).
    4. -
  4. ReturnIfAbrupt(items).
    5. -
  5. If mapfn was supplied, let f be mapfn; otherwise let f be undefined.
    6. -
  6. If f is not undefined, then -
      -
    1. If IsCallable(f) is false, then throw a TypeError - exception.
      2. -
    -
    7. -
  7. If thisArg was supplied, let t be thisArg; else let t be undefined.
    8. -
  8. Return TypedArrayFrom(constructor, undefined, items, - f, t).
    9. -
- -

The length property of the from method is 1.

- -
-

NOTE The from function is an intentionally generic factory method; it does not - require that its this value be a Typed Array constructor. Therefore it can be transferred to or inherited by - any other constructors that may be called with a single numeric argument. This function uses [[Put]] to store elements - into a newly created object and assume that the constructor sets the length property of the new object to - the argument value passed to it.

-
-
- -
-

22.2.2.1.1 Runtime Semantics: TypedArrayFrom( constructor, target, items, - mapfn, thisArg )

- -

When the TypedArrayFrom abstract operation is called with arguments constructor, target, items, - mapfn, and thisArg, the following steps are taken:

- -
    -
  1. Let C be constructor.
    2. -
  2. Assert: one of constructor and target is - undefined.
    3. -
  3. Assert: If constructor is not undefined, then IsConstructor(C) is true.
    4. -
  4. Assert: target is either undefined or an Object that has - been validated by the %TypedArray% constructor as described in 22.2.1.3
    5. -
  5. Assert: Type(items) is Object.
    6. -
  6. Assert: Type(mapfn) is either a callable Object or Undefined.
    7. -
  7. If mapfn is undefined, then let mapping be false.
    8. -
  8. else -
      -
    1. Let T be thisArg.
      2. -
    2. Let mapping be true
      3. -
    -
    9. -
  9. Let usingIterator be CheckIterable(items).
    10. -
  10. ReturnIfAbrupt(usingIterator).
    11. -
  11. If usingIterator is not undefined, then -
      -
    1. Let iterator be GetIterator(items, usingIterator).
      2. -
    2. ReturnIfAbrupt(iterator).
      3. -
    3. Let values be a new empty List.
      4. -
    4. Let next be true.
      5. -
    5. Repeat, while next is not false -
        -
      1. Let next be IteratorStep(iterator).
        2. -
      2. ReturnIfAbrupt(next).
        3. -
      -
      6. -
    6. If next is not false, then -
        -
      1. Let nextValue be IteratorValue(next).
        2. -
      2. ReturnIfAbrupt(nextValue).
        3. -
      3. Append nextValue to the end of the List - values.
        4. -
      -
      7. -
    7. Let len be the number of elements in values.
      8. -
    8. Let targetObj be TypedArrayAllocOrInit(C, - target, len).
      9. -
    9. ReturnIfAbrupt(targetObj).
      10. -
    10. Let k be 0.
      11. -
    11. Repeat, while k < len -
        -
      1. Let Pk be ToString(k).
        2. -
      2. Let kValue be the first element of values and remove that element from list.
        3. -
      3. If mapping is true, then -
          -
        1. Let mappedValue be the result of calling the [[Call]] internal method of mapfn with - T as thisArgument and (kValue, k) as argumentsList.
          2. -
        2. ReturnIfAbrupt(mappedValue).
          3. -
        -
        4. -
      4. Else, let mappedValue be kValue.
        5. -
      5. Let putStatus be Put(targetObj, Pk, - mappedValue, true).
        6. -
      6. ReturnIfAbrupt(putStatus).
        7. -
      7. Increase k by 1.
        8. -
      -
      12. -
    12. Assert: values is now an empty List.
      13. -
    13. Return targetObj.
      14. -
    -
    12. -
  12. Assert: items is not an Iterator so assume it is an array-like - object.
    13. -
  13. Let lenValue be Get(items, "length").
    14. -
  14. Let len be ToLength(lenValue).
    15. -
  15. ReturnIfAbrupt(len).
    16. -
  16. Let targetObj be TypedArrayAllocOrInit(C, target, - len).
    17. -
  17. ReturnIfAbrupt(targetObj).
    18. -
  18. Let k be 0.
    19. -
  19. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(items, Pk).
      3. -
    3. ReturnIfAbrupt(kValue).
      4. -
    4. If mapping is true, then -
        -
      1. Let mappedValue be the result of calling the [[Call]] internal method of mapfn with T - as thisArgument and (kValue, k) as argumentsList.
        2. -
      2. ReturnIfAbrupt(mappedValue).
        3. -
      -
      5. -
    5. Else, let mappedValue be kValue.
      6. -
    6. Let putStatus be Put(targetObj, Pk, - mappedValue, true).
      7. -
    7. ReturnIfAbrupt(putStatus).
      8. -
    8. Increase k by 1.
      9. -
    -
    20. -
  20. Return targetObj.
    21. -
-
- -
-

22.2.2.1.2 Runtime Semantics: TypedArrayAllocOrInit( constructor, target, - length)

- -

When the TypedArrayAllocOrInit abstract operation is called with arguments constructor, target, and length, the following steps are taken:

- -
    -
  1. Assert: one of constructor and target is - undefined.
    2. -
  2. Assert: If constructor is not undefined, then IsConstructor(constructor) is true.
    3. -
  3. Assert: target is either undefined or an Object that has - been validated by the %TypedArray% constructor as described in 22.2.1.3
    4. -
  4. Assert: Type(length) is Number.
    5. -
  5. If target is undefined, then -
      -
    1. Let targetObj be the result of calling the [[Construct]] internal method of constructor with - argument (length).
      2. -
    2. ReturnIfAbrupt(targetObj).
      3. -
    -
    6. -
  6. Else, -
      -
    1. Let targetObj be target.
      2. -
    2. Let constructorName be the string value of targetObj’s [[TypedArrayName]] internal slot.
      3. -
    3. Let elementType be the string value of the Element Type value in Table 44 for - constructorName.
      4. -
    4. Let data be AllocateArrayBuffer(%ArrayBuffer%).
      5. -
    5. ReturnIfAbrupt(data).
      6. -
    6. Let elementSize be the Element Size value in Table 44 for - constructorName.
      7. -
    7. Let byteLength be elementSize × length.
      8. -
    8. Let status be SetArrayBufferData(data, - byteLength)
      9. -
    9. Note: Side-effects of preceding steps may have already initialized targetObj.
      10. -
    10. If the value of targetObj’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception.
      11. -
    11. ReturnIfAbrupt(status).
      12. -
    12. Set targetObj’s [[ViewedArrayBuffer]] internal slot to data.
      13. -
    13. Set targetObj’s [[ByteLength]] internal - slot to byteLength.
      14. -
    14. Set targetObj’s [[ByteOffset]] internal - slot to 0.
      15. -
    15. Set targetObj’s [[ArrayLength]] internal slot to length.
      16. -
    -
    7. -
  7. Return targetObj.
    8. -
-
-
- -
-

22.2.2.2 - %TypedArray%.of ( ...items )

- -

When the of method is called with any number of arguments, the following steps are taken:

- -
    -
  1. Let len be the actual number of arguments passed to this function.
    2. -
  2. Let items be the List of arguments passed to this - function.
    3. -
  3. Let C be the this value.
    4. -
  4. If IsConstructor(C) is true, then -
      -
    1. Let newObj be the result of calling the [[Construct]] internal method of C with argument - (len).
      2. -
    2. ReturnIfAbrupt(newObj).
      3. -
    -
    5. -
  5. Else, -
      -
    1. Throw a TypeError exception.
      2. -
    -
    6. -
  6. Let k be 0.
    7. -
  7. Repeat, while k < len -
      -
    1. Let kValue be element k of items.
      2. -
    2. Let status be Put(newObj,Pk, kValue.[[value]], - true).
      3. -
    3. ReturnIfAbrupt(status).
      4. -
    4. Increase k by 1.
      5. -
    -
    8. -
  8. Return newObj.
    9. -
- -

The length property of the of method is 0.

- -
-

NOTE 1 The items argument is assumed to be a well-formed rest argument value.

-
- -
-

NOTE 2 The of function is an intentionally generic factory method; it does not - require that its this value be a TypedArray constructor. Therefore it can be transferred to or inherited - by other constructors that may be called with a single numeric argument. However, it does assume that constructor - creates and initializes a length property that is initialized to its argument value.

-
-
- -
-

22.2.2.3 %TypedArray%.prototype

- -

The initial value of %TypedArray%.prototype is the %TypedArrayPrototype% intrinsic object (22.2.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

-
- -
-

22.2.2.4 %TypedArray% [ @@create ] ( )

- -

The @@create method of %TypedArray% performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let proto be GetPrototypeFromConstructor(F, - "%TypedArrayPrototype%").
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Let obj be IntegerIndexedObjectCreate (proto).
    5. -
  5. Add a [[ViewedArrayBuffer]] internal slot to - obj and set its initial value to undefined.
    6. -
  6. Add a [[TypedArrayName]] internal slot to obj - and set its initial value to undefined .
    7. -
  7. Add a [[ByteLength]] internal slot to obj and - set its initial value to 0.
    8. -
  8. Add a [[ByteOffset]] internal slot to obj and - set its initial value to 0.
    9. -
  9. Add an [[ArrayLength]] internal slot to obj and - set its initial value to 0.
    10. -
  10. Return obj.
    11. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-
-

22.2.3 Properties of the %TypedArrayPrototype% Object

- -

The value of the [[Prototype]] internal slot of the - %TypedArrayPrototype% object is the standard built-in Object prototype object (19.1.3). The %TypedArrayPrototype% object is an ordinary object. - It does not have a [[ViewedArrayBuffer]] or or any other of the internal slots that are specific to TypedArray - instance objects.

-
- -
-

22.2.3.1 get %TypedArray%.prototype.buffer

- -

%TypedArray%.prototype.buffer is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then throw a TypeError exception.
    6. -
  6. Return buffer.
    7. -
-
- -
-

22.2.3.2 get %TypedArray%.prototype.byteLength

- -

%TypedArray%.prototype.byteLength is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then return 0.
    6. -
  6. Let size be the value of O’s [[ByteLength]] internal slot.
    7. -
  7. Return size.
    8. -
-
- -
-

22.2.3.3 get %TypedArray%.prototype.byteOffset

- -

%TypedArray%.prototype.byteOffset is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then return 0.
    6. -
  6. Let offset be the value of O’s [[ByteOffset]] internal slot.
    7. -
  7. Return offset.
    8. -
-
- -
-

22.2.3.4 %TypedArray%.prototype.constructor

- -

The initial value of %TypedArray%.prototype.constructor is the %TypedArray% intrinsic object.

-
- -
-

22.2.3.5 %TypedArray%.prototype.copyWithin (target, start, end = this.length - )

- -

%TypedArray%.prototype.copyWithin is a distinct function that implements the same algorithm as Array.prototype.copyWithin as defined in 22.1.3.3 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the copyWithin method is 2.

-
- -
-

22.2.3.6 %TypedArray%.prototype.entries ( )

- -

The initial value of the %TypedArray%.prototype.entries data property is the same built-in function object - as the Array.prototype.entries method defined in 22.1.3.4.

-
- -
-

22.2.3.7 %TypedArray%.prototype.every ( callbackfn [ , thisArg ] )

- -

%TypedArray%.prototype.every is a distinct function that implements the same algorithm as Array.prototype.every as defined in 22.1.3.5 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the every method is 1.

-
- -
-

22.2.3.8 %TypedArray%.prototype.fill (value [ , start [ , end ] ] )

- -

%TypedArray%.prototype.fill is a distinct function that implements the same algorithm as Array.prototype.fill as defined in 22.1.3.6 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the fill method is 1.

-
- -
-

22.2.3.9 %TypedArray%.prototype.filter ( callbackfn [ , thisArg ] )

- -

The interpretation and use of the arguments of %TypedArray%.prototype.filter are the same as for Array.prototype.filter as defined in 22.1.3.7.

- -

When the filter method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. Let len be the value of O’s [[ArrayLength]] internal slot.
    5. -
  5. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    6. -
  6. If thisArg was supplied, let T be thisArg; else let T be undefined.
    7. -
  7. Let C be Get(O, "constructor").
    8. -
  8. ReturnIfAbrupt(C).
    9. -
  9. If IsConstructor(C) is false, then -
      -
    1. Throw a TypeError exception.
      2. -
    -
    10. -
  10. Let kept be a new empty List.
    11. -
  11. Let k be 0.
    12. -
  12. Let captured be 0.
    13. -
  13. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(O, Pk).
      3. -
    3. ReturnIfAbrupt(kValue).
      4. -
    4. Let selected be the result of calling the [[Call]] internal method of callbackfn with T as - thisArgument and a List containing kValue, - k, and O as argumentsList.
      5. -
    5. ReturnIfAbrupt(selected).
      6. -
    6. If ToBoolean(selected) is true, then -
        -
      1. Append kValue to the end of kept.
        2. -
      2. Increase captured by 1.
        3. -
      -
      7. -
    7. Increase k by 1.
      8. -
    -
    14. -
  14. Let A be the result of calling the [[Construct]] internal method of C with argument - (captured).
    15. -
  15. ReturnIfAbrupt(A).
    16. -
  16. Let n be 0.
    17. -
  17. For each element e of kept -
      -
    1. Let status be Put(A, ToString(n), e, true ).
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    3. Increment n by 1.
      4. -
    -
    18. -
  18. Return A.
    19. -
- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the filter method is 1.

-
- -
-

22.2.3.10 %TypedArray%.prototype.find (predicate [ , thisArg ] )

- -

%TypedArray%.prototype.find is a distinct function that implements the same algorithm as Array.prototype.find as defined in 22.1.3.8 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the find method is 1.

-
- -
-

22.2.3.11 %TypedArray%.prototype.findIndex ( predicate [ , thisArg ] )

- -

%TypedArray%.prototype.findIndex is a distinct function that implements the same algorithm as Array.prototype.findIndex as defined in 22.1.3.9 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the findIndex method is 1.

-
- -
-

22.2.3.12 %TypedArray%.prototype.forEach ( callbackfn [ , thisArg ] )

- -

%TypedArray%.prototype.forEach is a distinct function that implements the same algorithm as Array.prototype.forEach as defined in 22.1.3.10 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the forEach method is 1.

-
- -
-

22.2.3.13 %TypedArray%.prototype.indexOf (searchElement [ , fromIndex ] )

- -

%TypedArray%.prototype.indexOf is a distinct function that implements the same algorithm as Array.prototype.indexOf as defined in 22.1.3.11 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the indexOf method is 1.

-
- -
-

22.2.3.14 %TypedArray%.prototype.join ( separator )

- -

%TypedArray%.prototype.join is a distinct function that implements the same algorithm as Array.prototype.join as defined in 22.1.3.12 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

-
- -
-

22.2.3.15 %TypedArray%.prototype.keys ( )

- -

The initial value of the %TypedArray%.prototype.keys data property is the same built-in function object as - the Array.prototype.keys method defined in 22.1.3.13.

-
- -
-

22.2.3.16 %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] - )

- -

%TypedArray%.prototype.lastIndexOf is a distinct function that implements the same algorithm as Array.prototype.lastIndexOf as defined in 22.1.3.14 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the lastIndexOf method is 1.

-
- -
-

22.2.3.17 get %TypedArray%.prototype.length

- -

%TypedArray%.prototype.length is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. Assert: O has [[ViewedArrayBuffer]] and [[ArrayLength]] internal - slots.
    5. -
  5. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    6. -
  6. If buffer is undefined, then return 0.
    7. -
  7. Let length be the value of O’s [[ArrayLength]] internal slot.
    8. -
  8. Return length.
    9. -
- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

-
- -
-

22.2.3.18 %TypedArray%.prototype.map ( callbackfn [ , thisArg ] )

- -

The interpretation and use of the arguments of %TypedArray%.prototype.map are the same as for Array.prototype.map as defined in 22.1.3.15.

- -

When the map method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. Let len be the value of O’s [[ArrayLength]] internal slot.
    5. -
  5. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    6. -
  6. If thisArg was supplied, let T be thisArg; else let T be undefined.
    7. -
  7. Let C be Get(O, "constructor").
    8. -
  8. ReturnIfAbrupt(C).
    9. -
  9. If IsConstructor(C) is true, then -
      -
    1. Let A be the result of calling the [[Construct]] internal method of C with argument List (len).
      2. -
    2. ReturnIfAbrupt(A).
      3. -
    -
    10. -
  10. Else, -
      -
    1. Throw a TypeError exception.
      2. -
    -
    11. -
  11. Let k be 0.
    12. -
  12. Repeat, while k < len -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(O, Pk).
      3. -
    3. ReturnIfAbrupt(kValue).
      4. -
    4. Let mappedValue be the result of calling the [[Call]] internal method of callbackfn with T - as thisArgument and a List containing - kValue, k, and O as argumentsList.
      5. -
    5. ReturnIfAbrupt(mappedValue).
      6. -
    6. Let status be Put(A, Pk, mappedValue, true - ).
      7. -
    7. ReturnIfAbrupt(status).
      8. -
    8. Increase k by 1.
      9. -
    -
    13. -
  13. Return A.
    14. -
- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the map method is 1.

-
- -
-

22.2.3.19 %TypedArray%.prototype.reduce ( callbackfn [ , initialValue ] )

- -

%TypedArray%.prototype.reduce is a distinct function that implements the same algorithm as Array.prototype.reduce as defined in 22.1.3.18 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the reduce method is 1.

-
- -
-

22.2.3.20 %TypedArray%.prototype.reduceRight ( callbackfn [ , initialValue ] - )

- -

%TypedArray%.prototype.reduceRight is a distinct function that implements the same algorithm as Array.prototype.reduceRight as defined in 22.1.3.19 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the reduceRight method is 1.

-
- -
-

22.2.3.21 %TypedArray%.prototype.reverse ( )

- -

%TypedArray%.prototype.reverse is a distinct function that implements the same algorithm as Array.prototype.reverse as defined in 22.1.3.20 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

-
- -
-

22.2.3.22 %TypedArray%.prototype.set(array [ , offset ] )

- -

Set multiple values in this TypedArray, reading the values from the object array. The optional - offset value indicates the first element index in this TypedArray where values are written. If omitted, it - is assumed to be 0.

- -
    -
  1. Assert: array does not have a [[TypedArrayName]] internal slot. If it does, the definition in 22.2.3.23 applies.
    2. -
  2. Let target be the this value.
    3. -
  3. If Type(target) is not Object, throw a TypeError - exception.
    4. -
  4. If target does not have a [[TypedArrayName]] internal slot, then throw a TypeError - exception.
    5. -
  5. Assert: target has a [[ViewedArrayBuffer]] internal slot.
    6. -
  6. Let targetBuffer be the value of target’s [[ViewedArrayBuffer]] internal slot.
    7. -
  7. If targetBuffer is undefined, then throw a TypeError exception.
    8. -
  8. Let targetLength be the value of target’s [[ArrayLength]] internal slot.
    9. -
  9. Let targetOffset be ToInteger (offset)
    10. -
  10. ReturnIfAbrupt(targetOffset).
    11. -
  11. If targetOffset < 0, then throw a RangeError exception.
    12. -
  12. Let targetName be the string value of target’s [[TypedArrayName]] internal slot.
    13. -
  13. Let targetElementSize be the Number value of the Element Size value specified in Table - 44 for targetName.
    14. -
  14. Let targetType be the string value of the Element Type value in Table 44 for - targetName.
    15. -
  15. Let targetByteOffset be the value of target’s [[ByteOffset]] internal slot.
    16. -
  16. Let src be ToObject(array).
    17. -
  17. ReturnIfAbrupt(src).
    18. -
  18. Let srcLen be Get(src, "length").
    19. -
  19. Let numberLength be ToNumber(srcLen).
    20. -
  20. Let srcLength be ToInteger(numberLength).
    21. -
  21. ReturnIfAbrupt(srcLength).
    22. -
  22. If numberLength ≠ srcLength or srcLength < 0, then throw a TypeError - exception.
    23. -
  23. If srcLength + targetOffset > targetLength, then throw a RangeError exception.
    24. -
  24. Let targetByteIndex be targetOffset × targetElementSize + targetByteOffset.
    25. -
  25. Let k be 0.
    26. -
  26. Let limit be targetByteIndex + targetElementSize × min(srcLength, - targetLength – targetOffset).
    27. -
  27. Repeat, while targetByteIndex < limit -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(src, Pk).
      3. -
    3. Let kNumber be ToNumber(kValue).
      4. -
    4. ReturnIfAbrupt(kNumber).
      5. -
    5. Perform SetValueInBuffer(targetBuffer, targetByteIndex, - targetType, kNumber).
      6. -
    6. Set k to k + 1.
      7. -
    7. Set targetByteIndex to targetByteIndex + targetElementSize.
      8. -
    -
    28. -
  28. Return undefined.
    29. -
-
- -
-

22.2.3.23 %TypedArray%.prototype.set(typedArray [, offset ] )

- -

Set multiple values in this TypedArray, reading the values from the typedArray argument object. The - optional offset value indicates the first element index in this TypedArray where values are written. If - omitted, it is assumed to be 0.

- -
    -
  1. Assert: typedArray has a [[TypedArrayName]] internal slot. If it does not, the definition in 22.2.3.22 applies.
    2. -
  2. Let target be the this value.
    3. -
  3. If Type(target) is not Object, throw a TypeError - exception.
    4. -
  4. If target does not have a [[TypedArrayName]] internal slot, then throw a TypeError - exception.
    5. -
  5. Assert: target has a [[ViewedArrayBuffer]] internal slot.
    6. -
  6. Let targetBuffer be the value of target’s [[ViewedArrayBuffer]] internal slot.
    7. -
  7. If targetBuffer is undefined, then throw a TypeError exception.
    8. -
  8. Let srcBuffer be the value of typedArray’s [[ViewedArrayBuffer]] internal slot.
    9. -
  9. If srcBuffer is undefined, then throw a TypeError exception.
    10. -
  10. Let targetLength be the value of target’s [[ArrayLength]] internal slot.
    11. -
  11. Let targetOffset be ToInteger (offset)
    12. -
  12. ReturnIfAbrupt(targetOffset).
    13. -
  13. If targetOffset < 0, then throw a RangeError exception.
    14. -
  14. Let targetName be the string value of target’s [[TypedArrayName]] internal slot.
    15. -
  15. Let targetType be the string value of the Element Type value in Table 44 for - targetName.
    16. -
  16. Let targetElementSize be the Number value of the Element Size value specified in Table - 44 for targetName.
    17. -
  17. Let targetByteOffset be the value of target’s [[ByteOffset]] internal slot.
    18. -
  18. Let srcName be the string value of typedArray’s [[TypedArrayName]] internal slot.
    19. -
  19. Let srcType be the string value of the Element Type value in Table 44 for - srcName .
    20. -
  20. Let srcElementSize be the Number value of the Element Size value specified in Table - 44 for srcName.
    21. -
  21. Let srcLength be the value of typedArray’s [[ArrayLength]] internal slot.
    22. -
  22. Let srcByteOffset be the value of typedArray’s [[ByteOffset]] internal slot.
    23. -
  23. If srcLength + targetOffset > targetLength, then throw a RangeError exception.
    24. -
  24. If SameValue(srcBuffer, targetBuffer) is true, then -
      -
    1. Let srcBuffer be CloneArrayBuffer(srcBuffer, - srcByteOffset).
      2. -
    2. Let srcByteIndex be 0.
      3. -
    -
    25. -
  25. Else, let srcByteIndex be srcByteOffset.
    26. -
  26. Let targetByteIndex be targetOffset × targetElementSize + targetByteOffset.
    27. -
  27. Let limit be targetByteIndex + targetElementSize × min(srcLength, - targetLength – targetOffset).
    28. -
  28. Repeat, while targetByteIndex < limit -
      -
    1. Let value be GetValueFromBuffer (srcBuffer, - srcByteIndex, srcType).
      2. -
    2. Let status be SetValueInBuffer (targetBuffer, - targetByteIndex, targetType, value).
      3. -
    3. Set srcByteIndex to srcByteIndex + srcElementSize.
      4. -
    4. Set targetByteIndex to targetByteIndex + targetElementSize.
      5. -
    -
    29. -
  29. Return undefined.
    30. -
-
- -
-

22.2.3.24 %TypedArray%.prototype.slice ( start, end )

- -

The interpretation and use of the arguments of %TypedArray%.prototype.slice are the same as for Array.prototype.slice as defined in 22.1.3.22. The following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. Let len be the value of O’s [[ArrayLength]] internal slot.
    5. -
  5. Let relativeStart be ToInteger(start).
    6. -
  6. ReturnIfAbrupt(relativeStart).
    7. -
  7. If relativeStart is negative, let k be max((len + relativeStart),0); else let k - be min(relativeStart, len).
    8. -
  8. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
    9. -
  9. ReturnIfAbrupt(relativeEnd).
    10. -
  10. If relativeEnd is negative, let final be max((len + relativeEnd),0); else let - final be min(relativeEnd, len).
    11. -
  11. Let count be max(final – k, 0).
    12. -
  12. Let C be Get(O, "constructor").
    13. -
  13. ReturnIfAbrupt(C).
    14. -
  14. If IsConstructor(C) is true, then -
      -
    1. Let A be the result of calling the [[Construct]] internal method of C with argument - (count).
      2. -
    2. ReturnIfAbrupt(A).
      3. -
    -
    15. -
  15. Else, -
      -
    1. Throw a TypeError exception.
      2. -
    -
    16. -
  16. Let n be 0.
    17. -
  17. Repeat, while k < final -
      -
    1. Let Pk be ToString(k).
      2. -
    2. Let kValue be Get(O, Pk).
      3. -
    3. ReturnIfAbrupt(kValue).
      4. -
    4. Let status be Put(A, ToString(n), kValue, true ).
      5. -
    5. ReturnIfAbrupt(status).
      6. -
    6. Increase k by 1.
      7. -
    7. Increase n by 1.
      8. -
    -
    18. -
  18. Return A.
    19. -
- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the slice method is 2.

-
- -
-

22.2.3.25 %TypedArray%.prototype.some ( callbackfn [ , thisArg ] )

- -

%TypedArray%.prototype.some is a distinct function that implements the same algorithm as Array.prototype.some as defined in 22.1.3.23 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of - "length". The implementation of the algorithm may be optimized with the knowledge that the this value - is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must - not introduce any observable changes in the specified behaviour of the algorithm.

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when this function is called.

- -

The length property of the some method is 1.

-
- -
-

22.2.3.26 %TypedArray%.prototype.sort ( comparefn )

- -

%TypedArray%.prototype.sort is a distinct function that, except as described below, implements the same - requirements as those of Array.prototype.sort as defined in 22.1.3.24. The implementation of the %TypedArray%.prototype.sort - specification may be optimized with the knowledge that the this value is an object that has a fixed length and - whose integer indexed properties are not sparse. The only internal methods of the this object that the algorithm - may call are [[Get]] and [[Set]].

- -

This function is not generic. If the this value is not a object with a [[TypedArrayName]] internal slot, a TypeError exception - is immediately thrown when it is called.

- -

Upon entry, the following steps are performed to initialize evaluation of the sort function. These steps - are used instead of the entry steps in 22.1.3.24:

- -
    -
  1. Let obj be the this value as the argument.
    2. -
  2. If obj does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    3. -
  3. Let len be the value of obj’s [[ArrayLength]] internal slot.
    4. -
- -

The following version of SortCompare is used by - %TypedArray%.prototype.sort. It performs a numeric comparison rather than the string comparsion used in 22.1.3.24.

- -

The Typed Array SortCompare abstract operation is called with two arguments j - and k, the following steps are taken:

- -
    -
  1. Let jString be ToString(j).
    2. -
  2. Let kString be ToString(k).
    3. -
  3. Let x be Get(obj,jString).
    4. -
  4. ReturnIfAbrupt(x).
    5. -
  5. Let y be the result of Get(obj, kString).
    6. -
  6. ReturnIfAbrupt(y).
    7. -
  7. Assert: Both Type(x) and Type(y) is Number.
    8. -
  8. If x and y are both NaN, return +0.
    9. -
  9. If x is NaN, return 1.
    10. -
  10. If y is NaN, return −1.
    11. -
  11. If the argument comparefn is not undefined, then -
      -
    1. If IsCallable(comparefn) is false, throw a TypeError - exception.
      2. -
    2. Return the result of calling the [[Call]] internal method of comparefn passing undefined as - thisArgument and with a List containing the values - of x and y as the argumentsList.
      3. -
    -
    12. -
  12. If x < y, return −1.
    13. -
  13. If x > y, return 1.
    14. -
  14. Return +0.
    15. -
- -
-

NOTE 1 Because NaN always compares greater than any other value, NaN property - values always sort to the end of the result.

-
-
- -
-

22.2.3.27 %TypedArray%.prototype.subarray( [ begin [ , end ] ] )

- -

Returns a new TypedArray object whose element types is the same as this TypedArray and whose ArrayBuffer - is the same as the ArrayBuffer of this TypedArray, referencing the elements at begin, inclusive, up to - end, exclusive. If either begin or end is negative, it refers to an index from the end of - the array, as opposed to from the beginning.

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    5. -
  5. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    6. -
  6. If buffer is undefined, then throw a TypeError exception.
    7. -
  7. Let srcLength be the value of O’s [[ArrayLength]] internal slot.
    8. -
  8. Let beginInt be ToInteger(begin)
    9. -
  9. ReturnIfAbrupt(beginInt).
    10. -
  10. If beginInt < 0, then let beginInt be srcLength + beginInt.
    11. -
  11. Let beginIndex be min(srcLength, max(0, beginInt)).
    12. -
  12. If end is undefined, then let end be srcLength.
    13. -
  13. Let endInt be ToInteger(end).
    14. -
  14. ReturnIfAbrupt(endInt).
    15. -
  15. If endInt < 0, then let endInt be srcLength + endInt.
    16. -
  16. Let endIndex be max(0,min(srcLength, endInt)).
    17. -
  17. If endIndex < beginIndex, then let endIndex be beginIndex.
    18. -
  18. Let newLength be endIndex - beginIndex.
    19. -
  19. Let constructorName be the string value of O’s [[TypedArrayName]] internal slot.
    20. -
  20. Let elementType be the string value of the Element Type value in Table 44 for - constructorName.
    21. -
  21. Let elementSize be the Number value of the Element Size value specified in Table 44 - for constructorName.
    22. -
  22. Let srcByteOffset be the value of O’s [[ByteOffset]] internal slot.
    23. -
  23. Let beginByteOffset be srcByteOffset + beginIndex × elementSize.
    24. -
  24. Let constructor be Get(O, "constructor").
    25. -
  25. ReturnIfAbrupt(constructor).
    26. -
  26. If IsConstructor(constructor) is false, then throw a TypeError - exception.
    27. -
  27. Let argumentsList be a List consisting of - buffer, beginByteOffset, and newLength.
    28. -
  28. Return the result of calling the [[Construct]] internal method of constructor with argumentsList as - the argument.
    29. -
-
- -
-

22.2.3.28 %TypedArray%.prototype.toLocaleString ( )

- -

The initial value of the %TypedArray%.prototype.toLocaleString data property is the same built-in function object as - the Array.prototype.toLocaleString method defined in 22.1.3.26.

-
- -
-

22.2.3.29 %TypedArray%.prototype.toString ( )

- -

The initial value of the %TypedArray%.prototype.toString data property is the same built-in function object as the Array.prototype.toString method defined in 22.1.3.27.

-
- -
-

22.2.3.30 %TypedArray%.prototype.values ( )

- -

The initial value of the %TypedArray%.prototype.values data property is the same built-in function object - as the Array.prototype.values method defined in 22.1.3.29.

-
- -
-

22.2.3.31 %TypedArray%.prototype [ @@iterator ] ( )

- -

The initial value of the @@iterator property is the same function object as the initial value of the - %TypedArray%.prototype.values property.

-
- -
-

22.2.3.32 get %TypedArray%.prototype [ @@toStringTag ]

- -

%TypedArray%.prototype[@@toStringTag] is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, throw a TypeError exception.
    4. -
  4. Let name be the value of O’s [[TypedArrayName]] internal slot.
    5. -
  5. If the value of O’s [[TypedArrayName]] internal slot is undefined, throw a - TypeError exception.
    6. -
  6. Assert: name is a String value.
    7. -
  7. Return name.
    8. -
- -

This property has the attributes { [[Enumerable]]: false, [[Configurable]]: true }.

- -

The initial value of the name property of this function is "get [Symbol.toStringTag]".

-
-
- -
-
-

22.2.4 The TypedArray Constructors

- -

Each of these TypedArray constructor objects has the structure described below, differing only in the name used - as the constructor name instead of TypedArray, in Table 44.

- -

When a TypedArray constructor is called as a function rather than as a constructor, it initializes a new - TypedArray object. The this value passed in the call must be an Object with a [[TypedArrayName]] internal slot and a [[ViewedArrayBuffer]] internal slot whose value is undefined. The constructor function initializes the this value using the argument values.

- -

The TypedArray constructors are designed to be subclassable. They may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - TypedArray behaviour must include a super call to the TypedArray constructor to initialize - subclass instances.

-
- -
-

22.2.4.1 - TypedArray( ... argumentsList)

- -

A TypedArray constructor with a list of arguments argumentsList performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, then throw a TypeError - exception.
    3. -
  3. If O does not have a [[TypedArrayName]] internal - slot, then throw a TypeError exception.
    4. -
  4. If the value of O’s [[TypedArrayName]] internal slot is not undefined, then throw a - TypeError exception.
    5. -
  5. Set O’s [[TypedArrayName]] internal slot - to the String value from the constructor name column in the row of Table 44 corresponding to - this constructor.
    6. -
  6. Let F be the TypedArray function object that was called.
    7. -
  7. Let realmF be F’s [[Realm]] internal - slot.
    8. -
  8. Let super be realmF.[[intrinsics]].[[%TypedArray%]].
    9. -
  9. Let argumentsList be the argumentsList argument of the [[Call]] internal method that invoked - F.
    10. -
  10. Return the result of calling the [[Call]] internal method of super with O and argumentsList as - arguments.
    11. -
-
- -
-

22.2.4.2 new TypedArray( ... argumentsList)

- -

A TypedArray constructor called as part of a new expression performs the following steps:

- -
    -
  1. Let F be the TypedArray function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return Construct(F, argumentsList).
    4. -
-
-
- -
-
-

22.2.5 Properties of the TypedArray Constructors

- -

The value of the [[Prototype]] internal slot of each - TypedArray constructor is the %TypedArray% intrinsic object (22.2.1).

- -

Each TypedArray constructor has a name property whose value is the String value of the constructor - name specifried for it in Table 44.

- -

Besides a length property (whose value is 3), each TypedArray constructor has the following - properties:

-
- -
-

22.2.5.1 TypedArray.BYTES_PER_ELEMENT

- -

The value of TypedArray.BYTES_PER_ELEMENT is the Number value of the Element Size value specified in Table 44 for TypedArray.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

22.2.5.2 TypedArray.prototype

- -

The initial value of TypedArray.prototype is the corresponding TypedArray prototype object (22.2.6).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

-
-
- -
-
-

22.2.6 Properties of TypedArray Prototype Objects

- -

The value of the [[Prototype]] internal slot of a - TypedArray prototype object is the standard built-in %TypedArrayPrototype% object (22.2.3). A TypedArray prototype object is an - ordinary object. It does not have a [[ViewedArrayBuffer]] or or any other of the internal slots that are specific to - TypedArray instance objects.

-
- -
-

22.2.6.1 TypedArray.prototype.BYTES_PER_ELEMENT

- -

The value of TypedArray.prototype.BYTES_PER_ELEMENT is the Number value of the Element Size value specified in - Table 44 for TypedArray.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

22.2.6.2 TypedArray.prototype.constructor

- -

The initial value of a TypedArray.prototype.constructor is the corresponding standard built-in TypedArray - constructor.

-
-
- -
-

22.2.7 Properties of TypedArray Instances

- -

TypedArray instances are Integer Indexed exotic objects. Each TypedArray instances inherits properties from - the corresponding TypedArray prototype object. Each TypedArray instances have the following internal slots: - [[TypedArrayName]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]], and [[ArrayLength]].

-
-
-
- -
-
-

23 Keyed - Collection

-
- -
-
-

23.1 Map - Objects

- -

Map objects are collections of key/value pairs where both the keys and values may be arbitrary ECMAScript language values. A distinct key value may only occur in one key/value - pair within the Map’s collection. Distinct key values are discriminated using the SameValueZero comparision algorithm.

- -

Map object must be implemented using either hash tables or other mechanisms that, on average, provide access times that - are sublinear on the number of elements in the collection. The data structures used in this Map objects specification is - only intended to describe the required observable semantics of Map objects. It is not intended to be a viable - implementation model.

-
- -
-
-

23.1.1 The - Map Constructor

- -

The Map constructor is the %Map% intrinsic object and the initial value of the Map property of the global - object. When Map is called as a function rather than as a constructor, it initializes its this value - with the internal state necessary to support the Map.prototype built-in methods.

- -

The Map constructor is designed to be subclassable. It may be used as the value in an extends - clause of a class definition. Subclass constructors that intend to inherit the specified Map behaviour must - include a super call to Map.

-
- -
-

23.1.1.1 - Map ( [ iterable ] )

- -

When the Map function is called with optional argument the following steps are taken:

- -
    -
  1. Let map be the this value.
    2. -
  2. If Type(map) is not Object then, throw a - TypeError exception.
    3. -
  3. If map does not have a [[MapData]] internal - slot, then throw a TypeError exception.
    4. -
  4. If map’s [[MapData]] internal slot is not - undefined, then throw a TypeError exception.
    5. -
  5. If iterable is not present, let iterable be undefined.
    6. -
  6. If iterable is either undefined or null, then let iter be undefined.
    7. -
  7. Else, -
      -
    1. Let iter be the result of GetIterator(iterable).
      2. -
    2. ReturnIfAbrupt(iter).
      3. -
    3. Let adder be the result of Get(map, "set").
      4. -
    4. ReturnIfAbrupt(adder).
      5. -
    5. If IsCallable(adder) is false, throw a TypeError - Exception.
      6. -
    -
    8. -
  8. If the value of map’s [[MapData]] internal - slot is not undefined, then throw a TypeError exception.
    9. -
  9. Assert: map has not been reentrantly initialized.
    10. -
  10. Set map’s [[MapData]] internal slot to a - new empty List.
    11. -
  11. If iter is undefined, then return map.
    12. -
  12. Repeat -
      -
    1. Let next be the result of IteratorStep(iter).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return NormalCompletion(map).
      4. -
    4. Let nextItem be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextItem).
      6. -
    6. If Type(nextItem) is not Object, then throw a - TypeError exception.
      7. -
    7. Let k be the result of Get(nextItem, "0").
      8. -
    8. ReturnIfAbrupt(k).
      9. -
    9. Let v be the result of Get(nextItem, "1").
      10. -
    10. ReturnIfAbrupt(v).
      11. -
    11. Let status be the result of calling the [[Call]] internal method of adder with map as - thisArgument and a List whose elements are k - and v as argumentsList.
      12. -
    12. ReturnIfAbrupt(status).
      13. -
    -
    13. -
- -
-

NOTE If the parameter iterable is present, it is expected to be an object that - implements an @@iterator method that returns an iterator object that produces a two element array-like object whose - first element is a value that will be used as an Map key and whose second element is the value to associate with that - key.

-
-
- -
-

23.1.1.2 new Map ( ... argumentsList )

- -

When Map is called as part of a new expression it is a constructor: it initializes a newly - created object.

- -

Map called as part of a new expression with argument list argumentsList performs the following - steps:

- -
    -
  1. Let F be the Map function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If Map is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

23.1.2 Properties of the Map Constructor

- -

The value of the [[Prototype]] internal slot of the Map - constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Map constructor has the following - properties:

-
- -
-

23.1.2.1 - Map.prototype

- -

The initial value of Map.prototype is the Map prototype object (23.1.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

23.1.2.2 - Map[ @@create ] ( )

- -

The @@create method of a Map function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, "%MapPrototype%", - ([[MapData]]) ).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

23.1.3 Properties of the Map Prototype Object

- -

The value of the [[Prototype]] internal slot of the Map - prototype object is the standard built-in Object prototype object (19.1.3). The Map prototype object is an ordinary object. It does - not have a [[MapData]] internal slot.

-
- -
-

23.1.3.1 Map.prototype.clear ( )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. Set p.[[key]] to empty.
      2. -
    2. Set p.[[value]] to empty.
      3. -
    -
    7. -
  7. Return undefined.
    8. -
- -
-

NOTE The existing [[MapData]] List is - preserved because there may be existing MapIterator objects that are suspended - midway through iterating over that List.

-
-
- -
-

23.1.3.2 Map.prototype.constructor

- -

The initial value of Map.prototype.constructor is the built-in Map constructor.

-
- -
-

23.1.3.3 Map.prototype.delete ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValueZero(p.[[key]], key) is true, then -
        -
      1. Set p.[[key]] to empty.
        2. -
      2. Set p.[[value]] to empty.
        3. -
      3. Return true.
        4. -
      -
      2. -
    -
    7. -
  7. Return false.
    8. -
- -
-

NOTE The value empty is used as a specification device to indicate that an entry has - been deleted. Actual implementations may take other actions such as physically removing the entry from internal data - structures.

-
-
- -
-

23.1.3.4 Map.prototype.entries ( )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. Return the result of calling the CreateMapIterator abstract operation with - arguments M and "key+value".
    3. -
-
- -
-

23.1.3.5 Map.prototype.forEach ( callbackfn [ , thisArg ] )

- -

NOTE callbackfn should be a function that accepts - three arguments. forEach calls callbackfn once for each key/value pair present in the map object, in - key insertion order. callbackfn is called only for keys of the map which actually exist; it is not called for keys - that have been deleted from the map.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

callbackfn is called with three arguments: the value of the item, the key of the item, and the Map - object being traversed.

- -

forEach does not directly mutate the object on which it is called but the object may be - mutated by the calls to callbackfn.

- -

When the forEach method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    6. -
  6. If thisArg was supplied, let T be thisArg; else let T be undefined.
    7. -
  7. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    8. -
  8. Repeat for each Record {[[key]], [[value]]} e that is an element of entries, in original key insertion - order -
      -
    1. If e.[[key]] is not empty, then -
        -
      1. Let funcResult be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - e.[[value]], e.[[key]], and M as argumentsList.
        2. -
      2. ReturnIfAbrupt(funcResult).
        3. -
      -
      2. -
    -
    9. -
  9. Return undefined.
    10. -
- -

The length property of the forEach method is 1.

-
- -
-

23.1.3.6 Map.prototype.get ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValueZero(p.[[key]], key) is true, then return - p.[[value]].
      2. -
    -
    7. -
  7. Return undefined.
    8. -
-
- -
-

23.1.3.7 Map.prototype.has ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValueZero(p.[[key]], key) is true, then return - true.
      2. -
    -
    7. -
  7. Return false.
    8. -
-
- -
-

23.1.3.8 Map.prototype.keys ( )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. Return the result of calling the CreateMapIterator abstract operation with - arguments M and "key".
    3. -
-
- -
-

23.1.3.9 Map.prototype.set ( key , value )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValueZero(p.[[key]], key) is true, then -
        -
      1. Set p.[[value]] to value.
        2. -
      2. Return M.
        3. -
      -
      2. -
    -
    7. -
  7. If key is −0, then let key be +0.
    8. -
  8. Let p be the Record {[[key]]: key, [[value]]: value}.
    9. -
  9. Append p as the last element of entries.
    10. -
  10. Return M.
    11. -
-
- -
-

23.1.3.10 get Map.prototype.size

- -

Map.prototype.size is an accessor property whose set accessor function is undefined. Its get - accessor function performs the following steps:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[MapData]] internal slot - throw a TypeError exception.
    4. -
  4. If M’s [[MapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - M’s [[MapData]] internal slot.
    6. -
  6. Let count be 0.
    7. -
  7. For each Record {[[key]], [[value]]} p that is an element of entries -
      -
    1. If p.[[key]] is not empty then -
        -
      1. Set count to count+1.
        2. -
      -
      2. -
    -
    8. -
  8. Return count.
    9. -
-
- -
-

23.1.3.11 Map.prototype.values ( )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. Return the result of calling the CreateMapIterator abstract operation with - arguments M and "value".
    3. -
-
- -
-

23.1.3.12 Map.prototype [ @@iterator ]( )

- -

The initial value of the @@iterator property is the same function object as the initial value of the entries - property.

-
- -
-

23.1.3.13 Map.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Map".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

23.1.4 Properties of Map Instances

- -

Map instances are ordinary objects that inherit properties from the Map prototype. Map instances also have a [[MapData]] - internal slot.

-
- -
-
-

23.1.5 Map Iterator Objects

- -

A Map Iterator is an object, that represents a specific iteration over some specific Map instance object. There is not - a named constructor for Map Iterator objects. Instead, map iterator objects are created by calling certain methods of Map - instance objects.

-
- -
-

23.1.5.1 CreateMapIterator Abstract Operation

- -

Several methods of Map objects return Iterator objects. The abstract operation CreateMapIterator with arguments - map and kind is used to create such iterator objects. It performs the following steps:

- -
    -
  1. If Type(map) is not Object, throw a TypeError - exception.
    2. -
  2. If map does not have a [[MapData]] internal - slot throw a TypeError exception.
    3. -
  3. If the value of map’s [[MapData]] internal - slot is undefined, then throw a TypeError exception.
    4. -
  4. Let iterator be the result of ObjectCreate(%MapIteratorPrototype%, ([[Map]], - [[MapNextIndex]], [[MapIterationKind]])).
    5. -
  5. Set iterator’s [[Map]] internal slot to - map.
    6. -
  6. Set iterator’s [[MapNextIndex]] internal - slot to 0.
    7. -
  7. Set iterator’s [[MapIterationKind]] internal - slot to kind.
    8. -
  8. Return iterator.
    9. -
-
- -
-
-

23.1.5.2 The %MapIteratorPrototype% Object

- -

All Map Iterator Objects inherit properties from the %MapIteratorPrototype% intrinsic object. The - %MapIteratorPrototype% intrinsic object is an ordinary object and its [[Prototype]] internal slot is the %ObjectPrototype% intrinsic object. In - addition, %MapIteratorPrototype% has the following properties:

-
- -
-

23.1.5.2.1 %MapIteratorPrototype%.next ( )

-
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have all of the internal slots of a Map Iterator Instance (23.1.5.3), throw a TypeError exception.
    4. -
  4. Let m be the value of the [[Map]] internal - slot of O.
    5. -
  5. Let index be the value of the [[MapNextIndex]] internal slot of O.
    6. -
  6. Let itemKind be the value of the [[MapIterationKind]] internal slot of O.
    7. -
  7. If m is undefined, then return CreateIterResultObject(undefined, true)
    8. -
  8. Assert: m has a [[MapData]] internal slot and m has been initialized so the - value of [[MapData]] is not undefined.
    9. -
  9. Let entries be the List that is the value of the - [[MapData]] internal slot of m.
    10. -
  10. Repeat while index is less than the total number of elements of entries. The number of elements must - be redetermined each time this method is evaluated. -
      -
    1. Let e be the Record {[[key]], [[value]]} that is the value of entries[index].
      2. -
    2. Set index to index+1;
      3. -
    3. Set the [[MapNextIndex]] internal slot of - O to index.
      4. -
    4. If e.[[key]] is not empty, then -
        -
      1. If itemKind is "key" then, let result be e.[[key]].
        2. -
      2. Else if itemKind is "value" then, let result be e.[[value]].
        3. -
      3. Else, -
          -
        1. Assert: itemKind is "key+value".
          2. -
        2. Let result be the result of performing ArrayCreate(2).
          3. -
        3. Assert: result is a new, well-formed Array object so - the following operations will never fail.
          4. -
        4. Call CreateDataProperty(result, "0", - e.[[key]]) .
          5. -
        5. Call CreateDataProperty(result, "1", - e.[[value]]).
          6. -
        -
        4. -
      4. Return CreateIterResultObject(result, false).
        5. -
      -
      5. -
    -
    11. -
  11. Set the [[Map]] internal slot of O to - undefined.
    12. -
  12. Return CreateIterResultObject(undefined, true).
    13. -
-
- -
-

23.1.5.2.2 %MapIteratorPrototype% [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

23.1.5.2.3 %MapIteratorPrototype% [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Map Iterator".

-
-
- -
-

23.1.5.3 Properties of Map Iterator Instances

- -

Map Iterator instances are ordinary objects that inherit properties from the %MapIteratorPrototype% intrinsic object. - Map Iterator instances are initially created with the internal slots described in Table 45.

- -
-
Table 45 — Internal Slots of Map Iterator Instances
- - - - - - - - - - - - - - - - - -
Internal SlotDescription
[[Map]]The Map object that is being iterated.
[[MapNextIndex]]The integer index of the next Map data element to be examined by this iterator.
[[MapIterationKind]]A string value that identifies what is to be returned for each element of the iteration. The possible values are: "key", "value", "key+value".
-
-
-
-
- -
-
-

23.2 Set - Objects

- -

Set objects are collections of ECMAScript language values. A distinct value - may only occur once as an element of a Set’s collection. Distinct values are discriminated using the SameValueZero comparision algorithm.

- -

Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that - are sublinear on the number of elements in the collection. The data structures used in this Set objects specification is - only intended to describe the required observable semantics of Set objects. It is not intended to be a viable - implementation model.

-
- -
-
-

23.2.1 The - Set Constructor

- -

The Set constructor is the %Set% intrinsic object and the initial value of the Set property of the global - object. When Set is called as a function rather than as a constructor, it initializes its this value - with the internal state necessary to support the Set.prototype built-in methods.

- -

The Set constructor is designed to be subclassable. It may be used as the value in an extends - clause of a class definition. Subclass constructors that intend to inherit the specified Set behaviour must - include a super call to Set.

-
- -
-

23.2.1.1 - Set ( [ iterable ] )

- -

When the Set function is called with optional argument iterable the following steps are - taken:

- -
    -
  1. Let set be the this value.
    2. -
  2. If Type(set) is not Object then, throw a - TypeError exception.
    3. -
  3. If set does not have a [[SetData]] internal - slot, then throw a TypeError exception.
    4. -
  4. If set’s [[SetData]] internal slot is not - undefined, then throw a TypeError exception.
    5. -
  5. If iterable is not present, let iterable be undefined.
    6. -
  6. If iterable is either undefined or null, then let iter be undefined.
    7. -
  7. Else, -
      -
    1. Let iter be the result of GetIterator(iterable).
      2. -
    2. ReturnIfAbrupt(iter).
      3. -
    3. Let adder be the result of Get(set, "add").
      4. -
    4. ReturnIfAbrupt(adder).
      5. -
    5. If IsCallable(adder) is false, throw a TypeError - Exception.
      6. -
    -
    8. -
  8. If the value of set’s [[SetData]] internal - slot is not undefined, then throw a TypeError exception.
    9. -
  9. Assert: set has not been reentrantly initialized.
    10. -
  10. Set set’s [[SetData]] internal slot to a - new empty List.
    11. -
  11. If iter is undefined, then return set.
    12. -
  12. Repeat -
      -
    1. Let next be the result of IteratorStep(iter).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return set.
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let status be the result of calling the [[Call]] internal method of adder with set as - thisArgument and a List whose sole element is - nextValue as argumentsList.
      7. -
    7. ReturnIfAbrupt(status).
      8. -
    -
    13. -
- -
-

NOTE Using a method call for inserting values during initialization enables subclasses to - that redefine add to still make a super call to the inherited constructor.

-
-
- -
-

23.2.1.2 new Set ( ...argumentsList )

- -

When Set is called as part of a new expression it is a constructor: it initializes a newly - created object. Set called as part of a new expression with argument list argumentsList performs the following - steps:

- -
    -
  1. Let F be the Set function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If Set is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

23.2.2 Properties of the Set Constructor

- -

The value of the [[Prototype]] internal slot of the Set - constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Set constructor has the following - properties:

-
- -
-

23.2.2.1 - Set.prototype

- -

The initial value of Set.prototype is the intrinsic %SetPrototype% object (23.2.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

23.2.2.2 - Set[ @@create ] ( )

- -

The @@create method of a Set function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, "%SetPrototype%", - ( [[SetData]])).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

23.2.3 Properties of the Set Prototype Object

- -

The value of the [[Prototype]] internal slot of the Set - prototype object is the standard built-in Object prototype object (19.1.3). The Set prototype object is an ordinary object. It does - not have a [[SetData]] internal slot.

-
- -
-

23.2.3.1 Set.prototype.add ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    6. -
  6. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValueZero(e, value) is true, then -
        -
      1. Return S.
        2. -
      -
      2. -
    -
    7. -
  7. If value is −0, then let value be +0.
    8. -
  8. Append value as the last element of entries.
    9. -
  9. Return S.
    10. -
-
- -
-

23.2.3.2 Set.prototype.clear ( )

- -

The following steps are taken:

- -
    -
  1. Let S be this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    6. -
  6. Repeat for each e that is an element of entries, -
      -
    1. Replace the element of entries whose value is e with an element whose value is empty.
      2. -
    -
    7. -
  7. Return undefined.
    8. -
-
- -
-

23.2.3.3 Set.prototype.constructor

- -

The initial value of Set.prototype.constructor is the built-in Set constructor.

-
- -
-

23.2.3.4 Set.prototype.delete ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    6. -
  6. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValueZero(e, value) is true, then -
        -
      1. Replace the element of entries whose value is e with an element whose value is empty.
        2. -
      2. Return true.
        3. -
      -
      2. -
    -
    7. -
  7. Return false.
    8. -
- -
-

NOTE The value empty is used as a specification device to indicate that an entry has - been deleted. Actual implementations may take other actions such as physically removing the entry from internal data - structures.

-
-
- -
-

23.2.3.5 Set.prototype.entries ( )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return the result of calling the CreateSetIterator abstract operation with - arguments S and "key+value".
    3. -
- -
-

NOTE For iteration purposes, a Set appears similar to a Map where each entry has the same - value for its key and value.

-
-
- -
-

23.2.3.6 Set.prototype.forEach ( callbackfn [ , thisArg ] )

- -
-

NOTE callbackfn should be a function that accepts three arguments. - forEach calls callbackfn once for each value present in the set object, in value insertion order. - callbackfn is called only for values of the Set which actually exist; it is not called for keys that have been - deleted from the set.

- -

If a thisArg parameter is provided, it will be used as the this value for each invocation of - callbackfn. If it is not provided, undefined is used instead.

- -

If callbackfn is an Arrow Function, this was lexically bound when the function was created so - thisArg will have no effect.

- -

callbackfn is called with three arguments: the first two arguments are a value contained in the Set. The same - value of passed for both arguments. The Set object being traversed is passed as the third argument.

- -

The callbackfn is called with three arguments to be consistent with the call back functions used by - forEach methods for Map and Array. For Sets, each item value is considered to be both the key and the - value.

- -

forEach does not directly mutate the object on which it is called but the object may be mutated by the - calls to callbackfn.

- -

Each value is normally visited only once. However, a value will be revisited if it is deleted after it has been - visited and then re-added before the to forEach call completes. Values that are deleted after the call to - forEach begins and before being visited are not visited unless the value is added again before the to - forEach call completes. New values added, after the call to forEach begins are visited.

-
- -

When the forEach method is called with one or two arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. If IsCallable(callbackfn) is false, throw a TypeError - exception.
    6. -
  6. If thisArg was supplied, let T be thisArg; else let T be undefined.
    7. -
  7. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    8. -
  8. Repeat for each e that is an element of entries, in original insertion order -
      -
    1. If e is not empty, then -
        -
      1. Let funcResult be the result of calling the [[Call]] internal method of callbackfn with - T as thisArgument and a List containing - e, e, and S as argumentsList.
        2. -
      2. ReturnIfAbrupt(funcResult).
        3. -
      -
      2. -
    -
    9. -
  9. Return undefined.
    10. -
- -

The length property of the forEach method is 1.

-
- -
-

23.2.3.7 Set.prototype.has ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    6. -
  6. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValueZero(e, value) is true, then return - true.
      2. -
    -
    7. -
  7. Return false.
    8. -
-
- -
-

23.2.3.8 Set.prototype.keys ( )

- -

The initial value of the keys property is the same function object as the initial value of the - values property.

- -
-

NOTE For iteration purposes, a Set appears similar to a Map where each entry has the same - value for its key and value.

-
-
- -
-

23.2.3.9 get Set.prototype.size

- -

Set.prototype.size is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[SetData]] internal slot - throw a TypeError exception.
    4. -
  4. If S’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[SetData]] internal slot.
    6. -
  6. Let count be 0.
    7. -
  7. For each e that is an element of entries -
      -
    1. If e is not empty then -
        -
      1. Set count to count+1.
        2. -
      -
      2. -
    -
    8. -
  8. Return count.
    9. -
-
- -
-

23.2.3.10 Set.prototype.values ( )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return the result of calling the CreateSetIterator abstract operation with - argument S and "value".
    3. -
-
- -
-

23.2.3.11 Set.prototype [@@iterator ] ( )

- -

The initial value of the @@iterator property is the same function object as the initial value of the - values property.

-
- -
-

23.2.3.12 Set.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Set".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

23.2.4 Properties of Set Instances

- -

Set instances are ordinary objects that inherit properties from the Set prototype. After initialization by the Set - constructor, Set instances also have a [[SetData]] internal - slot.

-
- -
-
-

23.2.5 Set Iterator Objects

- -

A Set Iterator is an ordinary object, with the structure defined below, that represents a specific iteration over some - specific Set instance object. There is not a named constructor for Set Iterator objects. Instead, set iterator objects - are created by calling certain methods of Set instance objects.

-
- -
-

23.2.5.1 CreateSetIterator Abstract Operation

- -

Several methods of Set objects return Iterator objects. The abstract operation CreateSetIterator with arguments - set and kind is used to create such iterator objects. It performs the following steps:

- -
    -
  1. If Type(set) is not Object, throw a TypeError - exception.
    2. -
  2. If set does not have a [[SetData]] internal - slot throw a TypeError exception.
    3. -
  3. If set’s [[SetData]] internal slot is - undefined, then throw a TypeError exception.
    4. -
  4. Let iterator be the result of ObjectCreate(%SetIteratorPrototype%, - ([[IteratedSet]], [[SetNextIndex]], [[SetIterationKind]])).
    5. -
  5. Set iterator’s [[IteratedSet]] internal - slot to set.
    6. -
  6. Set iterator’s [[SetNextIndex]] internal - slot to 0.
    7. -
  7. Set iterator’s [[SetIterationKind]] internal - slot to kind.
    8. -
  8. Return iterator.
    9. -
-
- -
-
-

23.2.5.2 The %SetIteratorPrototype% Object

- -

All Set Iterator Objects inherit properties from the %SetIteratorPrototype% intrinsic object. The - %SetIteratorPrototype% intrinsic object is an ordinary object and its [[Prototype]] internal slot is the %ObjectPrototype% intrinsic object. In - addition, %SetIteratorPrototype% has the following properties:

-
- -
-

23.2.5.2.1 %SetIteratorPrototype%.next ( )

-
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have all of the internal slots of a Set Iterator Instance (23.2.5.3), throw a TypeError exception.
    4. -
  4. Let s be the value of the [[IteratedSet]] internal slot of O.
    5. -
  5. Let index be the value of the [[SetNextIndex]] internal slot of O.
    6. -
  6. Let itemKind be the value of the [[SetIterationKind]] internal slot of O.
    7. -
  7. If s is undefined, then return CreateIterResultObject(undefined, true).
    8. -
  8. Assert: s has a [[SetData]] internal slot and s has been initialized so the - value of [[SetData]] is not undefined.
    9. -
  9. Let entries be the List that is the value of the - [[SetData]] internal slot of s.
    10. -
  10. Repeat while index is less than the total number of elements of entries. The number of elements must - be redetermined each time this method is evaluated. -
      -
    1. Let e be entries[index].
      2. -
    2. Set index to index+1;
      3. -
    3. Set the [[SetNextIndex]] internal slot of - O to index.
      4. -
    4. If e is not empty, then -
        -
      1. If itemKind is "key+value" then, -
          -
        1. Let result be the result of performing ArrayCreate(2).
          2. -
        2. Assert: result is a new, well-formed Array object so - the following operations will never fail.
          3. -
        3. Call CreateDataProperty(result, "0", - e) .
          4. -
        4. Call CreateDataProperty(result, "1", - e).
          5. -
        5. Return CreateIterResultObject(result, - false).
          6. -
        -
        2. -
      2. Return CreateIterResultObject(e, false).
        3. -
      -
      5. -
    -
    11. -
  11. Set the [[IteratedSet]] internal slot of O to - undefined.
    12. -
  12. Return CreateIterResultObject(undefined, true).
    13. -
-
- -
-

23.2.5.2.2 %SetIteratorPrototype% [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

23.2.5.2.3 %SetIteratorPrototype% [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Set Iterator".

-
-
- -
-

23.2.5.3 Properties of Set Iterator Instances

- -

Set Iterator instances are ordinary objects that inherit properties from the %SetIteratorPrototype% intrinsic object. - Set Iterator instances are initially created with the internal slots specified in Table 46.

- -
-
Table 46 — Internal Slots of Set Iterator Instances
- - - - - - - - - - - - - - - - - -
Internal SlotDescription
[[IteratedSet]]The Set object that is being iterated.
[[SetNextIndex]]The integer index of the next Set data element to be examined by this iterator
[[SetIterationKind]]A string value that identifies what is to be returned for each element of the iteration. The possible values are: "key", "value", "key+value". "key" and "value" have the same meaning.
-
-
-
-
- -
-
-

23.3 WeakMap - Objects

- -

WeakMap objects are collections of key/value pairs where the keys are objects and values may be arbitrary ECMAScript language values. A WeakMap may be queried to see if it contains an - key/value pair with a specific key, but no mechanisms is provided for enumerating the objects it holds as keys. If an object - that is being used as the key of a WeakMap key/value pair is only reachable by following a chain of references that start - within that WeakMap, then that key/value pair is inaccessible and is automatically removed from the WeakMap. WeakMap - implementations must detect and remove such key/value pairs and any associated resources.

- -

An implementation may impose an arbitrarily determined latency between the time a key/value pair of a WeakMap becomes - inaccessible and the time when the key/value pair is removed from the WeakMap. If this latency was observable to ECMAScript - program, it would be a source of indeterminacy that could impact program execution.  For that reason, an ECMAScript - implementation must not provide any means to observe a key of a WeakMap that does not require the observer to present the - observed key.

- -

WeakMap objects must be implemented using either hash tables or other mechanisms that, on average, provide access times - that are sublinear on the number of key/value pairs in the collection. The data structure used in this WeakMap objects - specification are only intended to describe the required observable semantics of WeakMap objects. It is not intended to be - a viable implementation model.

- -
-

NOTE WeakMap and WeakSets are intended to provide mechanisms for dynamically associating state - with an object in a manner that does not “leak” memory resources if, in the absence of the WeakMap or WeakSet, - the object otherwise became inaccessible and subject to resource reclamation by the implementation’s garbage - collection mechanisms. Achieving this characteristic requires coordination between the WeakMap or WeakSet implementation - and the garbage collector. The following references describe mechanism that may be useful to implementations of WeakMap - and WeakSets:

- -

Barry Hayes. 1997. Ephemerons: a new finalization mechanism. In Proceedings of the 12th ACM SIGPLAN conference on - Object-oriented programming, systems, languages, and applications (OOPSLA '97), A. Michael Berman (Ed.). ACM, New - York, NY, USA, 176-183. http://doi.acm.org/10.1145/263698.263733.

- -

Alexandra Barros, Roberto Ierusalimschy, Eliminating Cycles in Weak Tables. Journal of Universal Computer Science - - J.UCS , vol. 14, no. 21, pp. 3481-3497, 2008. http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak

-
-
- -
-
-

23.3.1 - The WeakMap Constructor

- -

The WeakMap constructor is the %WeakMap% intrinsic object and the initial value of the WeakMap property of - the global object. When WeakMap is called as a function rather than as a constructor, it initializes its - this value with the internal state necessary to support the WeakMap.prototype built-in methods.

- -

The WeakMap constructor is designed to be subclassable. It may be used as the value in an - extends clause of a class definition. Subclass constructors that intend to inherit the specified - WeakMap behaviour must include a super call to WeakMap.

-
- -
-

23.3.1.1 WeakMap ( [ iterable ] )

- -

When the WeakMap function is called with optional argument iterable the following steps are - taken:

- -
    -
  1. Let map be the this value.
    2. -
  2. If Type(map) is not Object then, throw a - TypeError exception.
    3. -
  3. If map does not have a [[WeakMapData]] internal - slot, then throw a TypeError exception.
    4. -
  4. If map’s [[WeakMapData]] internal slot is - not undefined, then throw a TypeError exception.
    5. -
  5. If iterable is not present, let iterable be undefined.
    6. -
  6. If iterable is either undefined or null, then let iter be undefined.
    7. -
  7. Else, -
      -
    1. Let iter be the result of GetIterator(iterable).
      2. -
    2. ReturnIfAbrupt(iter).
      3. -
    3. Let adder be the result of Get(map, "set").
      4. -
    4. ReturnIfAbrupt(adder).
      5. -
    5. If IsCallable(adder) is false, throw a TypeError - Exception.
      6. -
    -
    8. -
  8. If the value of map’s [[WeakMapData]] internal slot is not undefined, then throw a - TypeError exception.
    9. -
  9. Assert: map has not been reentrantly initialized.
    10. -
  10. Set map’s [[WeakMapData]] internal slot - to a new empty List.
    11. -
  11. If iter is undefined, then return map.
    12. -
  12. Repeat -
      -
    1. Let next be the result of IteratorStep(iter).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return NormalCompletion(map).
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. If Type(nextValue) is not Object, then throw a - TypeError exception
      7. -
    7. Let k be the result of Get(nextValue, "0").
      8. -
    8. ReturnIfAbrupt(k).
      9. -
    9. Let v be the result of Get(nextValue, "1").
      10. -
    10. ReturnIfAbrupt(v).
      11. -
    11. Let status be the result of calling the [[Call]] internal method of adder with map as - thisArgument and a List whose elements are k - and v as argumentsList.
      12. -
    12. ReturnIfAbrupt(status).
      13. -
    -
    13. -
- -
-

NOTE If the parameter iterable is present, it is expected to be an object that - implements an @@iterator method that returns an iterator object that produces a two element array-like object whose - first element is a value that will be used as a WeakMap key and whose second element is the value to associate with that - key.

-
-
- -
-

23.3.1.2 new WeakMap ( ...argumentsList )

- -

When WeakMap is called as part of a new expression it is a constructor: it initializes a - newly created object.

- -

WeakMap called as part of a new expression with argument list argumentsList performs the following - steps:

- -
    -
  1. Let F be the WeakMap function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If WeakMap is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

23.3.2 Properties of the WeakMap Constructor

- -

The value of the [[Prototype]] internal slot of the - WeakMap constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the WeakMap constructor has the following - properties:

-
- -
-

23.3.2.1 WeakMap.prototype

- -

The initial value of WeakMap.prototype is the WeakMap prototype object (23.3.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

23.3.2.2 WeakMap[ @@create ] ( )

- -

The @@create method of a WeakMap object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%WeakMapPrototype%", ( [[WeakMapData]] )).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

23.3.3 Properties of the WeakMap Prototype Object

- -

The value of the [[Prototype]] internal slot of the - WeakMap prototype object is the standard built-in Object prototype object (19.1.3). The WeakMap prototype object is an ordinary object. It - does not have a [[WeakMapData]] internal slot.

-
- -
-

23.3.3.1 WeakMap.prototype.clear ( )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[WeakMapData]] internal - slot throw a TypeError exception.
    4. -
  4. If M’s [[WeakMapData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Set the value of M’s [[WeakMapData]] internal - slot to a new empty List.
    6. -
  6. Return undefined.
    7. -
-
- -
-

23.3.3.2 WeakMap.prototype.constructor

- -

The initial value of WeakMap.prototype.constructor is the built-in WeakMap constructor.

-
- -
-

23.3.3.3 WeakMap.prototype.delete ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[WeakMapData]] internal - slot throw a TypeError exception.
    4. -
  4. Let entries be the List that is the value of - M’s [[WeakMapData]] internal slot.
    5. -
  5. If entries is undefined, then throw a TypeError exception.
    6. -
  6. If Type(key) is not Object, then return - false.
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValue(p.[[key]], key) is true, then -
        -
      1. Set p.[[key]] to empty.
        2. -
      2. Set p.[[value]] to empty.
        3. -
      3. Return true.
        4. -
      -
      2. -
    -
    8. -
  8. Return false.
    9. -
- -
-

NOTE The value empty is used as a specification device to indicate that an entry has - been deleted. Actual implementations may take other actions such as physically removing the entry from internal data - structures.

-
-
- -
-

23.3.3.4 WeakMap.prototype.get ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[WeakMapData]] internal - slot throw a TypeError exception.
    4. -
  4. Let entries be the List that is the value of - M’s [[WeakMapData]] internal slot.
    5. -
  5. If entries is undefined, then throw a TypeError exception.
    6. -
  6. If Type(key) is not Object, then return - undefined.
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValue(p.[[key]], key) is true, then return - p.[[value]].
      2. -
    -
    8. -
  8. Return undefined.
    9. -
-
- -
-

23.3.3.5 WeakMap.prototype.has ( key )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[WeakMapData]] internal - slot throw a TypeError exception.
    4. -
  4. Let entries be the List that is the value of - M’s [[WeakMapData]] internal slot.
    5. -
  5. If entries is undefined, then throw a TypeError exception.
    6. -
  6. If Type(key) is not Object, then return - false.
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValue(p.[[key]], key) is true, then return - true.
      2. -
    -
    8. -
  8. Return false.
    9. -
-
- -
-

23.3.3.6 WeakMap.prototype.set ( key , value )

- -

The following steps are taken:

- -
    -
  1. Let M be the this value.
    2. -
  2. If Type(M) is not Object, then throw a TypeError - exception.
    3. -
  3. If M does not have a [[WeakMapData]] internal - slot throw a TypeError exception.
    4. -
  4. Let entries be the List that is the value of - M’s [[WeakMapData]] internal slot.
    5. -
  5. If entries is undefined, then throw a TypeError exception.
    6. -
  6. If Type(key) is not Object, then throw a TypeError - exception.
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of entries, -
      -
    1. If p.[[key]] is not empty and SameValue(p.[[key]], key) is true, then -
        -
      1. Set p.[[value]] to value.
        2. -
      2. Return M.
        3. -
      -
      2. -
    -
    8. -
  8. Let p be the Record {[[key]]: key, [[value]]: value}.
    9. -
  9. Append p as the last element of entries.
    10. -
  10. Return M.
    11. -
-
- -
-

23.3.3.7 WeakMap.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "WeakMap".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

23.3.4 Properties of WeakMap Instances

- -

WeakMap instances are ordinary objects that inherit properties from the WeakMap prototype. WeakMap instances also have a - [[WeakMapData]] internal slot.

-
-
- -
-
-

23.4 WeakSet - Objects

- -

WeakSet objects are collections of objects. A distinct object may only occur once as an element of a WeakSet’s - collection. A WeakSet may be queried to see if it contains a specific object, but no mechanisms is provided for enumerating - the objects it holds. If an object that is contain by a WeakSet is only reachable by following a chain of references that - start within that WeakSet, then that object is inaccessible and is automatically removed from the WeakSet. WeakSet - implementations must detect and remove such objects and any associated resources.

- -

An implementation may impose an arbitrarily determined latency between the time an object contained in a WeakSet becomes - inaccessible and the time when the object is removed from the WeakSet. If this latency was observable to ECMAScript program, - it would be a source of indeterminacy that could impact program execution.  For that reason, an ECMAScript - implementation must not provide any means to determine if a WeakSet contains a particular object that does not require the - observer to present the observed object.

- -

WeakSet objects must be implemented using either hash tables or other mechanisms that, on average, provide access times - that are sublinear on the number of elements in the collection. The data structure used in this WeakSet objects - specification is only intended to describe the required observable semantics of WeakSet objects. It is not intended to be a - viable implementation model.

- -
-

NOTE See the NOTE in 23.3.

-
-
- -
-
-

23.4.1 - The WeakSet Constructor

- -

The WeakSet constructor is the %WeakSet% intrinsic object and the initial value of the WeakSet property of - the global object. When WeakSet is called as a function rather than as a constructor, it initializes its - this value with the internal state necessary to support the WeakSet.prototype built-in methods.

- -

The WeakSet constructor is designed to be subclassable. It may be used as the value in an - extends clause of a class definition. Subclass constructors that intend to inherit the specified - WeakSet behaviour must include a super call to WeakSet.

-
- -
-

23.4.1.1 WeakSet ( [ iterable ] )

- -

When the WeakSet function is called with optional argument iterable the following steps are - taken:

- -
    -
  1. Let set be the this value.
    2. -
  2. If Type(set) is not Object then, throw a - TypeError exception.
    3. -
  3. If set does not have a [[WeakSetData]] internal - slot, then throw a TypeError exception.
    4. -
  4. If set’s [[WeakSetData]] internal slot is - not undefined, then throw a TypeError exception.
    5. -
  5. If iterable is not present, let iterable be undefined.
    6. -
  6. If iterable is either undefined or null, then let iter be undefined.
    7. -
  7. Else, -
      -
    1. Let iter be the result of GetIterator(iterable).
      2. -
    2. ReturnIfAbrupt(iter).
      3. -
    3. Let adder be the result of Get(set, "add").
      4. -
    4. ReturnIfAbrupt(adder).
      5. -
    5. If IsCallable(adder) is false, throw a TypeError - Exception.
      6. -
    -
    8. -
  8. If the value of set’s [[WeakSetData]] internal slot is not undefined, then throw a - TypeError exception.
    9. -
  9. Assert: set has not been reentrantly initialized.
    10. -
  10. Set set’s [[WeakSetData]] internal slot - to a new empty List.
    11. -
  11. If iter is undefined, then return set.
    12. -
  12. Repeat -
      -
    1. Let next be the result of IteratorStep(iter).
      2. -
    2. ReturnIfAbrupt(next).
      3. -
    3. If next is false, then return NormalCompletion(set).
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. ReturnIfAbrupt(nextValue).
      6. -
    6. Let status be the result of calling the [[Call]] internal method of adder with set as - thisArgument and a List whose sole element is - nextValue as argumentsList.
      7. -
    7. ReturnIfAbrupt(status).
      8. -
    -
    13. -
-
- -
-

23.4.1.2 new WeakSet ( ...argumentsList)

- -

When WeakSet is called as part of a new expression it is a constructor: it initializes a - newly created object.

- -

WeakSet called as part of a new expression with argument list argumentsList performs the following - steps:

- -
    -
  1. Let F be the WeakSet function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If WeakSet is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

23.4.2 Properties of the WeakSet Constructor

- -

The value of the [[Prototype]] internal slot of the - WeakSet constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the WeakSet constructor has the following - properties:

-
- -
-

23.4.2.1 WeakSet.prototype

- -

The initial value of WeakSet.prototype is the intrinsic %WeakSetPrototype% object (23.4.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

23.4.2.2 WeakSet [ @@create ] ( )

- -

The @@create method of a WeakSet function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%WeakSetPrototype%", ( [[WeakSetData]] )).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

23.4.3 Properties of the WeakSet Prototype Object

- -

The value of the [[Prototype]] internal slot of the - WeakSet prototype object is the standard built-in Object prototype object (19.1.3). The WeakSet prototype object is an ordinary object. It - does not have a [[WeakSetData]] internal slot.

-
- -
-

23.4.3.1 WeakSet.prototype.add ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[WeakSetData]] internal - slot throw a TypeError exception.
    4. -
  4. If S’s [[WeakSetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. If Type(value) is not Object, then throw a - TypeError exception.
    6. -
  6. Let entries be the List that is the value of - S’s [[WeakSetData]] internal slot.
    7. -
  7. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValue(e, value) is true, then -
        -
      1. Return S.
        2. -
      -
      2. -
    -
    8. -
  8. Append value as the last element of entries.
    9. -
  9. Return S.
    10. -
-
- -
-

23.4.3.2 WeakSet.prototype.clear ( )

- -

The following steps are taken:

- -
    -
  1. Let S be this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[WeakSetData]] internal - slot throw a TypeError exception.
    4. -
  4. If S’s [[WeakSetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Set the value of S’s [[WeakSetData]] internal - slot to a new empty List.
    6. -
  6. Return undefined.
    7. -
-
- -
-

23.4.3.3 WeakSet.prototype.constructor

- -

The initial value of WeakSet.prototype.constructor is the %WeakSet% intrinsic object.

-
- -
-

23.4.3.4 WeakSet.prototype.delete ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[WeakSetData]] internal - slot throw a TypeError exception.
    4. -
  4. If S’s [[WeakSetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. If Type(value) is not Object, then return - false.
    6. -
  6. Let entries be the List that is the value of - S’s [[WeakSetData]] internal slot.
    7. -
  7. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValue(e, value) is true, then -
        -
      1. Replace the element of entries whose value is e with an element whose value is empty.
        2. -
      2. Return true.
        3. -
      -
      2. -
    -
    8. -
  8. Return false.
    9. -
- -
-

NOTE The value empty is used as a specification device to indicate that an entry has - been deleted. Actual implementations may take other actions such as physically removing the entry from internal data - structures.

-
-
- -
-

23.4.3.5 WeakSet.prototype.has ( value )

- -

The following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. If Type(S) is not Object, then throw a TypeError - exception.
    3. -
  3. If S does not have a [[WeakSetData]] internal - slot throw a TypeError exception.
    4. -
  4. If S’s [[WeakSetData]] internal slot is - undefined, then throw a TypeError exception.
    5. -
  5. Let entries be the List that is the value of - S’s [[WeakSetData]] internal slot.
    6. -
  6. If Type(value) is not Object, then return - false.
    7. -
  7. Repeat for each e that is an element of entries, -
      -
    1. If e is not empty and SameValue(e, value), then return true.
      2. -
    -
    8. -
  8. Return false.
    9. -
-
- -
-

23.4.3.6 WeakSet.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "WeakSet".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

23.4.4 Properties of WeakSet Instances

- -

WeakSet instances are ordinary objects that inherit properties from the WeakSet prototype. After initialization by the - WeakSet constructor, WeakSet instances also have a [[WeakSetData]] internal slot.

-
-
-
- -
-
-

24 Structured - Data

-
- -
-
-

24.1 - ArrayBuffer Objects

-
- -
-
-

24.1.1 Abstract Operations For ArrayBuffer Objects

-
- -
-

24.1.1.1 AllocateArrayBuffer( constructor )

- -

The abstract operation AllocateArrayBuffer with argument constructor is used to create an uninitialized - ArrayBuffer object. It performs the following steps:

- -
    -
  1. Let obj be OrdinaryCreateFromConstructor(constructor, - "%ArrayBufferPrototype%", ( [[ArrayBufferData]], [[ArrayBufferByteLength]]) ).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Set the [[ArrayBufferByteLength]] internal slot of - obj to 0.
    4. -
  4. Return obj.
    5. -
-
- -
-

24.1.1.2 NeuterArrayBuffer( arrayBuffer )

- -

The abstract operation NeuterArrayBuffer with argument arrayBuffer performs the following steps:

- -
    -
  1. Assert: Type(arrayBuffer) is Object and it has [[ArrayBufferData]] - and [[ArrayBufferByteLength]] internal slots.
    2. -
  2. Set arrayBuffer’s [[ArrayBufferData]] internal slot to null.
    3. -
  3. Set arrayBuffer’s [[ArrayBufferByteLength]] internal slot to 0.
    4. -
  4. Return NormalCompletion(null).
    5. -
- -
-

NOTE Neutering an ArrayBuffer instance disassociated the Data - Block used as its backing store from the instance and sets the byte length of the buffer to 0. No operations - defined by this specification uses the NeuterArrayBuffer abstract operation. However, an ECMAScript implementation or - host environment may define such operations.

-
-
- -
-

24.1.1.3 SetArrayBufferData( arrayBuffer, bytes )

- -

The abstract operation SetArrayBufferData with arguments arrayBuffer - and bytes is used to initialize the storage block encapsulated by an ArrayBuffer object. It performs the - following steps:

- -
    -
  1. ReturnIfAbrupt(arrayBuffer).
    2. -
  2. Assert: Type(arrayBuffer) is Object and it has an - [[ArrayBufferData]] internal slot.
    3. -
  3. Assert: bytes is a positive integer.
    4. -
  4. Let block be CreateByteDataBlock(bytes).
    5. -
  5. ReturnIfAbrupt(block).
    6. -
  6. Set arrayBuffer’s [[ArrayBufferData]] internal slot to block.
    7. -
  7. Set arrayBuffer’s [[ArrayBufferByteLength]] internal slot to bytes.
    8. -
  8. Return arrayBuffer.
    9. -
-
- -
-

24.1.1.4 CloneArrayBuffer( srcBuffer, srcByteOffset )

- -

The abstract operation CloneArrayBuffer takes two parameters, an - ArrayBuffer srcBuffer and an integer srcByteOffset. It creates a new ArrayBufer whose data is a copy - of srcBuffer’s data starting at srcByteOffset. This operation performs the following - steps:

- -
    -
  1. Assert: Type(srcBuffer) is Object and it has an [[ArrayBufferData]] - internal slot.
    2. -
  2. Let srcBlock be the value of srcBuffer’s [[ArrayBufferData]] internal slot.
    3. -
  3. If srcBlock is undefined or null, then throw a TypeError exception.
    4. -
  4. Let srcLength be the value of srcBuffer’s [[ArrayBufferByteLength]] internal slot.
    5. -
  5. Let bufferConstructor be Get(srcBuffer, "constructor").
    6. -
  6. ReturnIfAbrupt(bufferConstructor).
    7. -
  7. Assert: srcByteOffset ≤ srcLength.
    8. -
  8. Let cloneLength be srcLength – srcByteOffset.
    9. -
  9. If bufferConstructor is undefined, then let bufferConstructor be %ArrayBuffer%.
    10. -
  10. Let targetBuffer be AllocateArrayBuffer(bufferConstructor).
    11. -
  11. Let status be SetArrayBufferData(targetBuffer, - cloneLength).
    12. -
  12. ReturnIfAbrupt(status).
    13. -
  13. Let targetBlock be the value of targetBuffer’s [[ArrayBufferData]] internal slot.
    14. -
  14. Perform CopyDataBlockBytes(targetBlock, 0, srcBlock, - srcByteOffset, cloneLength).
    15. -
  15. Return targetBuffer.
    16. -
-
- -
-

24.1.1.5 GetValueFromBuffer ( arrayBuffer, byteIndex, type, isLittleEndian - )

- -

The abstract operation GetValueFromBuffer takes four parameters, an - ArrayBuffer arrayBuffer, an integer byteIndex, a String type, and optionally a Boolean - isLittleEndian. This operation performs the following steps:

- -
    -
  1. Assert: There are sufficient bytes in arrayBuffer starting at - byteIndex to represent a value of type.
    2. -
  2. Assert: byteIndex is a positive integer.
    3. -
  3. Let block be arrayBuffer’s [[ArrayBufferData]] internal slot.
    4. -
  4. If block is undefined or null, then throw a TypeError exception.
    5. -
  5. Let elementSize be the Number value of the Element Size value specified in Table 44 - for Element Type type.
    6. -
  6. Let rawValue be a List of elementSize containing, in - order, the elementSize bytes starting at byteIndex of block.
    7. -
  7. If isLittleEndian is not present, set isLittleEndian to either true or false. The choice - is implementation dependent and should be the alternative that is most efficient for the implementation. An - implementation must use the same value each time this step is executed and the same value must be used for the - corresponding step in the SetValueInBuffer abstract operation.
    8. -
  8. If isLittleEndian is false, reverse the order of the elements of rawValue.
    9. -
  9. If type is “Float32” , then -
      -
    1. Let value be the byte elements of rawValue concatenated and interpreted as a little-endian bit - string encoding of an IEEE 754-2008 binary32 value.
      2. -
    2. If value is an IEEE 754-2008 binary32 NaN value, return the NaN Number value.
      3. -
    3. Return the Number value that corresponds to value.
      4. -
    -
    10. -
  10. If type is “Float64” , then -
      -
    1. Let value be the byte elements of rawValue concatenated and interpreted as a little-endian bit - string encoding of an IEEE 754-2008 binary64 value.
      2. -
    2. If value is an IEEE 754-2008 binary64 NaN value, return the NaN Number value.
      3. -
    3. Return the Number value that corresponds to value.
      4. -
    -
    11. -
  11. If the first character of type is "U", then -
      -
    1. Let intValue be the byte elements of rawValue concatenated and interpreted as a bit string - encoding of an unsigned little-endian binary number.
      2. -
    -
    12. -
  12. Else -
      -
    1. Let intValue be the byte elements of rawValue concatenated and interpreted as a bit string - encoding of a binary little-endian 2’s complement number of bit length elementSize × 8.
      2. -
    -
    13. -
  13. Return the Number value that corresponds to intValue.
    14. -
-
- -
-

24.1.1.6 SetValueInBuffer ( arrayBuffer, byteIndex, type, value, - isLittleEndian )

- -

The abstract operation SetValueInBuffer takes five parameters, an - ArrayBuffer arrayBuffer, an integer byteIndex, a String type, a Number value, and - optionally a Boolean isLittleEndian. This operation performs the following steps:

- -
    -
  1. Assert: There are sufficient bytes in arrayBuffer starting at - byteIndex to represent a value of type.
    2. -
  2. Assert: byteIndex is a positive integer.
    3. -
  3. Let block be arrayBuffer’s [[ArrayBufferData]] internal slot.
    4. -
  4. If block is undefined or null, then throw a TypeError exception.
    5. -
  5. Let elementSize be the Number value of the Element Size specified in Table 44 for - Element Type type.
    6. -
  6. If isLittleEndian is not present, set isLittleEndian to either true or false. The choice - is implementation dependent and should be the alternative that is most efficient for the implementation. An - implementation must use the same value each time this step is executed and the same value must be used for the - corresponding step in the GetValueFromBuffer abstract operation.
    7. -
  7. If type is “Float32” , then -
      -
    1. Set rawValue to a List containing the 4 bytes that - are the result of converting value to IEEE-868-2008 binary32 format using “Round to nearest, ties - to even” rounding mode. If isLittleEndian is false, the bytes are arranged in big endian - order. Otherwise, the bytes are arranged in little endian order. If value is NaN, rawValue - may be set to any implementation choosen non-signaling NaN encoding.
      2. -
    -
    8. -
  8. Else, if type is “Float64” , then -
      -
    1. Set rawValue to a List containing the 8 bytes that - are the IEEE-868-2008 binary64 format encoding of value. If isLittleEndian is false, the - bytes are arranged in big endian order. Otherwise, the bytes are arranged in little endian order. If - value is NaN, rawValue may be set to any implementation choosen non-signaling NaN - encoding.
      2. -
    -
    9. -
  9. Else, -
      -
    1. Let n be the Element Size value in Table 44 for the row containing the value of - type as its Element Type entry.
      2. -
    2. Let convOp be the abstract operation named in the Conversion Operation column in Table 44 for Element Type type.
      3. -
    3. Let intValue be the result of calling convOp with value as its argument .
      4. -
    4. If intValue ≥ 0, then -
        -
      1. Let rawBytes be a List containing the - n-byte binary encoding of intValue. If isLittleEndian is false, the bytes are - ordered in big endian order. Otherwise, the bytes are ordered in little endian order.
        2. -
      -
      5. -
    5. Else, -
        -
      1. Let rawBytes be a List containing the - n-byte binary 2’s complement encoding of intValue. If isLittleEndian is - false, the bytes are ordered in big endian order. Otherwise, the bytes are ordered in little endian - order.
        2. -
      -
      6. -
    -
    10. -
  10. Store the individual bytes of rawBytes in order starting at position byteIndex of block.
    11. -
  11. Return NormalCompletion (undefined).
    12. -
-
-
- -
-
-

24.1.2 The ArrayBuffer Constructor

- -

The ArrayBuffer constructor is the %ArrayBuffer% intrinsic object and the initial value of the ArrayBuffer - property of the global object. When ArrayBuffer is called as a function rather than as a constructor, its - this value must be an Object with an [[ArrayBufferData]] internal slot whose value is undefined. The ArrayBuffer constructor initializes the this value using the argument - values.

- -

The ArrayBuffer constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - ArrayBuffer behaviour must include a super call to the ArrayBuffer constructor to - initialize subclass instances.

-
- -
-

24.1.2.1 ArrayBuffer( length )

- -

ArrayBuffer called as function with argument length performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object or if O does not have an - [[ArrayBufferData]] internal slot or if the value of - O’s [[ArrayBufferData]] internal slot is - not undefined, then -
      -
    1. Throw a TypeError exception.
      2. -
    -
    3. -
  3. Let numberLength be ToNumber(length).
    4. -
  4. Let byteLength be ToLength(numberLength).
    5. -
  5. ReturnIfAbrupt(byteLength).
    6. -
  6. If SameValueZero(numberLength, byteLength) is false, then - throw a RangeError exception.
    7. -
  7. If the value of O’s [[ArrayBufferData]] internal slot is not undefined, then -
      -
    1. Throw a TypeError exception.
      2. -
    -
    8. -
  8. Return the result of SetArrayBufferData(O, byteLength).
    9. -
-
- -
-

24.1.2.2 new ArrayBuffer( ...argumentsList )

- -

ArrayBuffer called as part of a new expression performs the following steps:

- -
    -
  1. Let F be the ArrayBuffer function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If ArrayBuffer is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

24.1.3 Properties of the ArrayBuffer Constructor

- -

The value of the [[Prototype]] internal slot of the - ArrayBuffer constructor is the Function prototype object (19.2.3).

- -

Besides its length property (whose value is 1), the ArrayBuffer constructor has the following - properties:

-
- -
-

24.1.3.1 ArrayBuffer.isView ( arg )

- -

The isView function takes one argument arg, and performs the following steps are taken:

- -
    -
  1. If Type(arg) is not Object, return false.
    2. -
  2. If arg has a [[ViewedArrayBuffer]] internal - slot, then return true.
    3. -
  3. Return false.
    4. -
-
- -
-

24.1.3.2 ArrayBuffer.prototype

- -

The initial value of ArrayBuffer.prototype is the ArrayBuffer prototype object (24.1.4).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

24.1.3.3 ArrayBuffer[ @@create ] ( )

- -

The @@create method of an ArrayBuffer function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Return the result of calling AllocateArrayBuffer(F).
    3. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-
-

24.1.4 Properties of the ArrayBuffer Prototype Object

- -

The value of the [[Prototype]] internal slot of the - ArrayBuffer prototype object is the standard built-in Object prototype object (19.1.3). The ArrayBuffer prototype object is an ordinary object. - It does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.

-
- -
-

24.1.4.1 get ArrayBuffer.prototype.byteLength

- -

ArrayBuffer.prototype.byteLength is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have an [[ArrayBufferData]] internal - slot throw a TypeError exception.
    4. -
  4. If the value of O’s [[ArrayBufferData]] internal slot is undefined or null, then - throw a TypeError exception.
    5. -
  5. If the value of O’s [[ArrayBufferData]] internal slot is null, then return 0.
    6. -
  6. Let length be the value of O’s [[ArrayBufferByteLength]] internal slot.
    7. -
  7. Return length.
    8. -
-
- -
-

24.1.4.2 ArrayBuffer.prototype.constructor

- -

The initial value of ArrayBuffer.prototype.constructor is the standard built-in ArrayBuffer constructor.

-
- -
-

24.1.4.3 ArrayBuffer.prototype.slice ( start , end )

- -

The following steps are taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have an [[ArrayBufferData]] internal - slot throw a TypeError exception.
    4. -
  4. If the value of O’s [[ArrayBufferData]] internal slot is undefined or null, then - throw a TypeError exception.
    5. -
  5. Let len be the value of O’s [[ArrayBufferByteLength]] internal slot.
    6. -
  6. Let relativeStart be ToInteger(start).
    7. -
  7. ReturnIfAbrupt(relativeStart).
    8. -
  8. If relativeStart is negative, let first be max((len + relativeStart),0); else let - first be min(relativeStart, len).
    9. -
  9. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
    10. -
  10. ReturnIfAbrupt(relativeEnd).
    11. -
  11. If relativeEnd is negative, let final be max((len + relativeEnd),0); else let - final be min(relativeEnd, len).
    12. -
  12. Let newLen be max(final-first,0).
    13. -
  13. Let ctor be the result of Get(O, "constructor").
    14. -
  14. ReturnIfAbrupt(ctor).
    15. -
  15. If IsConstructor(ctor) is false, then throw a TypeError - exception.
    16. -
  16. Let new be the result of calling the [[Construct]] internal method of ctor with a new List containing the single element newLen.
    17. -
  17. ReturnIfAbrupt(new).
    18. -
  18. If new does not have an [[ArrayBufferData]] internal slot throw a TypeError exception.
    19. -
  19. If the value of new’s [[ArrayBufferData]] internal slot is undefined, then throw a - TypeError exception.
    20. -
  20. If the value of new’s [[ArrayBufferByteLength]] internal slot < newLen, then throw a - TypeError exception.
    21. -
  21. Let fromBuf be the value of O’s [[ArrayBufferData]] internal slot.
    22. -
  22. Let toBuf be the value of new’s [[ArrayBufferData]] internal slot.
    23. -
  23. Perform CopyDataBlockBytes(toBuf, 0, fromBuf, first, - newLen).
    24. -
  24. Return new.
    25. -
-
- -
-

24.1.4.4 ArrayBuffer.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "ArrayBuffer".

-
-
- -
-

24.1.5 Properties of the ArrayBuffer Instances

- -

ArrayBuffer instances inherit properties from the ArrayBuffer prototype object. ArrayBuffer instances each have an - [[ArrayBufferData]] internal slot and an - [[ArrayBufferByteLength]] internal slot.

- -

ArrayBuffer instances whose [[ArrayBufferData]] is null are considered to be neutered and all operators to - access or modify data contained in the ArrayBuffer instance will fail.

-
-
- -
-
-

24.2 DataView - Objects

-
- -
-
-

24.2.1 Abstract Operations For DataView Objects

-
- -
-

24.2.1.1 - GetViewValue ( view, requestIndex, isLittleEndian, type )

- -

The abstract operation GetViewValue with arguments view, requestIndex, isLittleEndian, - and type is used by functions on DataView instances is to retrieve values from the view’s buffer. It - performs the following steps:

- -
    -
  1. If Type(view) is not Object, throw a TypeError - exception.
    2. -
  2. If view does not have a [[DataView]] internal - slot, then throw a TypeError exception.
    3. -
  3. Let buffer be the value of view’s [[ViewedArrayBuffer]] internal slot.
    4. -
  4. If buffer is undefined, then throw a TypeError exception.
    5. -
  5. Let numberIndex be ToNumber(requestIndex)
    6. -
  6. Let getIndex be ToInteger(numberIndex).
    7. -
  7. ReturnIfAbrupt(getIndex).
    8. -
  8. If numberIndex ≠ getIndex or getIndex < 0, then throw a RangeError exception.
    9. -
  9. Let isLittleEndian be ToBoolean(isLittleEndian).
    10. -
  10. ReturnIfAbrupt(isLittleEndian).
    11. -
  11. Let viewOffset be the value of view’s [[ByteOffset]] internal slot.
    12. -
  12. Let viewSize be the value of view’s [[ByteLength]] internal slot.
    13. -
  13. Let elementSize be the Number value of the Element Size value specified in Table 44 - for type.
    14. -
  14. If getIndex +elementSize > viewSize, then throw a RangeError exception.
    15. -
  15. Let bufferIndex be getIndex + viewOffset.
    16. -
  16. Return the result of GetValueFromBuffer(buffer, bufferIndex, - type, isLittleEndian).
    17. -
-
- -
-

24.2.1.2 - SetViewValue ( view, requestIndex, isLittleEndian, type, value )

- -

The abstract operation SetViewValue with arguments view, requestIndex, isLittleEndian, - type, and value is used by functions on DataView instances to store values into the view’s - buffer. It performs the following steps:

- -
    -
  1. If Type(view) is not Object, throw a TypeError - exception.
    2. -
  2. If view does not have a [[DataView]] internal - slot, then throw a TypeError exception.
    3. -
  3. Let buffer be the value of view’s [[ViewedArrayBuffer]] internal slot.
    4. -
  4. If buffer is undefined, then throw a TypeError exception.
    5. -
  5. Let numberIndex be ToNumber(requestIndex)
    6. -
  6. Let getIndex be ToInteger(numberIndex).
    7. -
  7. ReturnIfAbrupt(getIndex).
    8. -
  8. If numberIndex ≠ getIndex or getIndex < 0, then throw a RangeError exception.
    9. -
  9. Let isLittleEndian be ToBoolean(isLittleEndian).
    10. -
  10. ReturnIfAbrupt(isLittleEndian).
    11. -
  11. Let viewOffset be the value of view’s [[ByteOffset]] internal slot.
    12. -
  12. Let viewSize be the value of view’s [[ByteLength]] internal slot.
    13. -
  13. Let elementSize be the Number value of the Element Size value specified in Table 44 - for type.
    14. -
  14. If getIndex +elementSize > viewSize, then throw a RangeError exception.
    15. -
  15. Let bufferIndex be getIndex + viewOffset.
    16. -
  16. Return the result of SetValueInBuffer(buffer, bufferIndex, - type, value, isLittleEndian).
    17. -
- -
-

NOTE The algorithms for GetViewValue and SetViewValue are - identical except for their final steps.

-
-
-
- -
-
-

24.2.2 The DataView Constructor

- -

The DataView constructor is the %DataView% intrinsic object and the initial value of the DataView property - of the global object. When DataView is called as a function rather than as a constructor, it initializes its - this value with the internal state necessary to support the DataView.prototype internal methods.

- -

The DataView constructor is designed to be subclassable. It may be used as the value of an - extends clause of a class declaration. Subclass constructors that intended to inherit the specified - DataView behaviour must include a super call to the DataView constructor to - initialize subclass instances.

-
- -
-

24.2.2.1 DataView (buffer [ , byteOffset [ , byteLength ] ] )

- -

DataView called with arguments buffer, - byteOffset, and length performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object or if O does not have a - [[DataView]] internal slot, throw a TypeError - exception.
    3. -
  3. Assert: O has a [[ViewedArrayBuffer]] internal slot.
    4. -
  4. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then -
      -
    1. Throw a TypeError exception.
      2. -
    -
    5. -
  5. If Type(buffer) is not Object, then throw a - TypeError exception.
    6. -
  6. If buffer does not have an [[ArrayBufferData]] internal slot, then throw a TypeError - exception.
    7. -
  7. If the value of buffer’s [[ArrayBufferData]] internal slot is undefined, then throw a - TypeError exception.
    8. -
  8. Let numberOffset be ToNumber(byteOffset).
    9. -
  9. Let offset be ToInteger(numberOffset).
    10. -
  10. ReturnIfAbrupt(offset).
    11. -
  11. If numberOffset ≠ offset or offset < 0, then throw a RangeError exception.
    12. -
  12. Let bufferByteLength be the value of buffer’s [[ArrayBufferByteLength]] internal slot.
    13. -
  13. If offset > bufferByteLength, then throw a RangeError exception.
    14. -
  14. If byteLength is undefined, then -
      -
    1. Let viewByteLength be bufferByteLength – offset.
      2. -
    -
    15. -
  15. Else, -
      -
    1. Let numberLength be ToNumber(byteLength).
      2. -
    2. Let viewLength be ToInteger (numberLength).
      3. -
    3. ReturnIfAbrupt(viewLength).
      4. -
    4. If numberLength ≠ viewLength or viewLength < 0, then throw a RangeError - exception.
      5. -
    5. Let viewByteLength be viewLength.
      6. -
    6. If offset+viewByteLength > bufferByteLength, then throw a RangeError - exception.
      7. -
    -
    16. -
  16. If the value of O’s [[ViewedArrayBuffer]] internal slot is not undefined, then throw a - TypeError exception,
    17. -
  17. Set O’s [[ViewedArrayBuffer]] internal - slot to buffer.
    18. -
  18. Set O’s [[ByteLength]] internal slot to - viewByteLength.
    19. -
  19. Set O’s [[ByteOffset]] internal slot to - offset.
    20. -
  20. Return O.
    21. -
-
- -
-

24.2.2.2 new DataView ( ...argumentsList )

- -

When DataView is called as part of a new expression it performs the following steps:

- -
    -
  1. Let F be the function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If DataView is implemented as an ECMAScript function - object, its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

24.2.3 Properties of the DataView Constructor

- -

The value of the [[Prototype]] internal slot of the - DataView constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 3), the DataView constructor has the following - properties:

-
- -
-

24.2.3.1 DataView.prototype

- -

The initial value of DataView.prototype is the DataView prototype object (24.2.4).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

24.2.3.2 DataView [ @@create ] ( )

- -

The @@create method of a DataView function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%DataViewPrototype%", ( [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]]) ).
    3. -
  3. Set the value of obj’s [[DataView]] internal - slot to true.
    4. -
  4. Return obj.
    5. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

- -
-

NOTE The value of the [[DataView]] internal slot is not used within this specification. The - simple presense of that internal slot is used within the - specification to identify objects created using this @@create method.

-
-
-
- -
-
-

24.2.4 Properties of the DataView Prototype Object

- -

The value of the [[Prototype]] internal slot of the - DataView prototype object is the standard built-in Object prototype object (19.1.3). The DataView prototype object is an ordinary object. It - does not have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], or [[ByteOffset]] internal slot.

-
- -
-

24.2.4.1 get DataView.prototype.buffer

- -

DataView.prototype.buffer is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then throw a TypeError exception.
    6. -
  6. Return buffer.
    7. -
-
- -
-

24.2.4.2 get DataView.prototype.byteLength

- -

DataView.prototype.byteLength is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then throw a TypeError exception.
    6. -
  6. Let size be the value of O’s [[ByteLength]] internal slot.
    7. -
  7. Return size.
    8. -
-
- -
-

24.2.4.3 get DataView.prototype.byteOffset

- -

DataView.prototype.byteOffset is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have a [[ViewedArrayBuffer]] internal - slot throw a TypeError exception.
    4. -
  4. Let buffer be the value of O’s [[ViewedArrayBuffer]] internal slot.
    5. -
  5. If buffer is undefined, then throw a TypeError exception.
    6. -
  6. Let offset be the value of O’s [[ByteOffset]] internal slot.
    7. -
  7. Return offset.
    8. -
-
- -
-

24.2.4.4 DataView.prototype.constructor

- -

The initial value of DataView.prototype.constructor is the standard built-in DataView constructor.

-
- -
-

24.2.4.5 DataView.prototype.getFloat32 ( byteOffset [ , littleEndian ] )

- -

When the getFloat32 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Float32").
    4. -
-
- -
-

24.2.4.6 DataView.prototype.getFloat64 ( byteOffset [ , littleEndian ] )

- -

When the getFloat64 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Float64").
    4. -
-
- -
-

24.2.4.7 DataView.prototype.getInt8 ( byteOffset )

- -

When the getInt8 method is called with argument byteOffset the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. Return the result of GetViewValue(v, byteOffset, true, - "Int8").
    3. -
-
- -
-

24.2.4.8 DataView.prototype.getInt16 ( byteOffset [ , littleEndian ] )

- -

When the getInt16 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Int16").
    4. -
-
- -
-

24.2.4.9 DataView.prototype.getInt32 ( byteOffset [ , littleEndian ] )

- -

When the getInt32 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be undefined.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Int32").
    4. -
-
- -
-

24.2.4.10 DataView.prototype.getUint8 ( byteOffset )

- -

When the getUint8 method is called with argument byteOffset the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. Return the result of GetViewValue(v, byteOffset, true, - "Uint8").
    3. -
-
- -
-

24.2.4.11 DataView.prototype.getUint16 ( byteOffset [ , littleEndian ] )

- -

When the getUint16 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Uint16").
    4. -
-
- -
-

24.2.4.12 DataView.prototype.getUint32 ( byteOffset [ , littleEndian ] )

- -

When the getUint32 method is called with argument byteOffset and optional argument - littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of GetViewValue(v, byteOffset, littleEndian, - "Uint32").
    4. -
-
- -
-

24.2.4.13 DataView.prototype.setFloat32 ( byteOffset, value [ , littleEndian ] - )

- -

When the setFloat32 method is called with arguments byteOffset and value and - optional argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Float32", value).
    4. -
-
- -
-

24.2.4.14 DataView.prototype.setFloat64 ( byteOffset, value [ , littleEndian ] - )

- -

When the setFloat64 method is called with arguments byteOffset and value and - optional argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Float64", value).
    4. -
-
- -
-

24.2.4.15 DataView.prototype.setInt8 ( byteOffset, value )

- -

When the setInt8 method is called with arguments byteOffset and value the following - steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. Return the result of SetViewValue(v, byteOffset, true, - "Int8", value).
    3. -
-
- -
-

24.2.4.16 DataView.prototype.setInt16 ( byteOffset, value [ , littleEndian ] - )

- -

When the setInt16 method is called with arguments byteOffset and value and optional - argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Int16", value).
    4. -
-
- -
-

24.2.4.17 DataView.prototype.setInt32 ( byteOffset, value [ , littleEndian ] - )

- -

When the setInt32 method is called with arguments byteOffset and value and optional - argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Int32", value).
    4. -
-
- -
-

24.2.4.18 DataView.prototype.setUint8 ( byteOffset, value )

- -

When the setUint8 method is called with arguments byteOffset and value the following - steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. Return the result of SetViewValue(v, byteOffset, true, - "Uint8", value).
    3. -
-
- -
-

24.2.4.19 DataView.prototype.setUint16 ( byteOffset, value [ , littleEndian ] - )

- -

When the setUint16 method is called with arguments byteOffset and value and optional - argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Uint16", value).
    4. -
-
- -
-

24.2.4.20 DataView.prototype.setUint32 ( byteOffset, value [ , littleEndian ] - )

- -

When the setUint32 method is called with arguments byteOffset and value and optional - argument littleEndian the following steps are taken:

- -
    -
  1. Let v be the this value.
    2. -
  2. If littleEndian is not present, then let littleEndian be false.
    3. -
  3. Return the result of SetViewValue(v, byteOffset, littleEndian, - "Uint32", value).
    4. -
-
- -
-

24.2.4.21 DataView.prototype[ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "DataView".

-
-
- -
-

24.2.5 Properties of DataView Instances

- -

DataView instances are ordinary objects that inherit properties from the DataView prototype object. DataView instances - each have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], and [[ByteOffset]] internal slots.

-
-
- -
-
-

24.3 The JSON - Object

- -

The JSON object is a single ordinary object that contains two functions, parse and stringify, that - are used to parse and construct JSON texts. The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange - format used in this specification is exactly that described by ECMA-404.

- -

Conforming implementations of JSON.parse and JSON.stringify must support the exact interchange format described in this specification - without any deletions or extensions to the format.

- -

The value of the [[Prototype]] internal slot of the JSON - object is the standard built-in Object prototype object (19.1.3). The value of the [[Extensible]] internal slot of the JSON object is set to true.

- -

The JSON object does not have a [[Construct]] internal method; it is not possible to use the JSON object as a constructor - with the new operator.

- -

The JSON object does not have a [[Call]] internal method; it is not possible to invoke the JSON object as a function.

-
- -
-
-

24.3.1 - JSON.parse ( text [ , reviver ] )

- -

The parse function parses a JSON text (a JSON-formatted String) and produces an ECMAScript value. The JSON - format is a subset of the syntax for ECMAScript literals, Array Initializers and Object Initializers. After parsing, JSON - objects are realized as ECMAScript objects. JSON arrays are realized as ECMAScript Array instances. JSON strings, numbers, - booleans, and null are realized as ECMAScript Strings, Numbers, Booleans, and null.

- -

The optional reviver parameter is a function that takes two parameters, (key and value). It can - filter and transform the results. It is called with each of the key/value pairs produced by the parse, and - its return value is used instead of the original value. If it returns what it received, the structure is not modified. If - it returns undefined then the property is deleted from the result.

- -
    -
  1. Let JText be ToString(text).
    2. -
  2. ReturnIfAbrupt(JText).
    3. -
  3. Parse JText interpreted as UTF-16 encoded Unicode points as a JSON text as specified in
    ECMA-404. Throw a - SyntaxError exception if JText is not a valid JSON text as defined in that specification.
    4. -
  4. Let scriptText be the result of concatenating "(", JText, and ");".
    5. -
  5. Let completion be the result of parsing and evaluating scriptText as if it was the source text of an - ECMAScript Script. but using the alternative definition of DoubleStringCharacter provided below. The - extended PropertyDefinitionEvaluation semantics defined in B.3.1 must not be used during the evaluation.
    6. -
  6. Let unfiltered be completion.[[value]].
    7. -
  7. Assert: unfiltered will be either a primitive value or an object - that is defined by either an ArrayLiteral or an ObjectLiteral.
    8. -
  8. If IsCallable(reviver) is true, then -
      -
    1. Let root be ObjectCreate(%ObjectPrototype%).
      2. -
    2. Let status be the result of CreateDataProperty(root, the - empty String, unfiltered).
      3. -
    3. Assert: status is true.
      4. -
    4. Return the result of calling the abstract operation Walk, passing root and the - empty String. The abstract operation Walk is described below.
      5. -
    -
    9. -
  9. Else -
      -
    1. Return unfiltered.
      2. -
    -
    10. -
- -

JSON allows Unicode code points U+2028 and U+2029 to directly appear in String literals without - using an escape sequence. This is enabled by using the following alternative definition of DoubleStringCharacter when parsing scriptText in step 5:

- -
-
DoubleStringCharacter ::
-
SourceCharacter but not one of " or \ or U+0000 through U+001F
-
\ EscapeSequence
-
- -
    -
  • -

    The CV of DoubleStringCharacter :: SourceCharacter but not one of " or \ or U+0000 through U+001F - is the UTF-16Encoding (10.1.1) of the code point value of SourceCharacter.

    -
    • -
- -
-

NOTE The syntax of a valid JSON text is a subset of the ECMAScript PrimaryExpression - syntax. Hence a valid JSON text is also a valid PrimaryExpression. Step 3 above verifies that JText - conforms to that subset. When scriptText is parsed and evaluated as a Script the result will be either a - String, Number, Boolean, or Null primitive value or an Object defined as if by an ArrayLiteral or - ObjectLiteral.

-
-
- -
-

24.3.1.1 Runtime - Semantics: Walk Abstract Operation

- -

The abstract operation Walk is a recursive abstract operation that takes two parameters: a holder object and - the String name of a property in that object. Walk uses the value of reviver that was originally - passed to the above parse function.

- -
    -
  1. Let val be the result of Get(holder, name).
    2. -
  2. ReturnIfAbrupt(val).
    3. -
  3. If val is an object, then -
      -
    1. If val is an exotic Array object then -
        -
      1. Set I to 0.
        2. -
      2. Let len be the result of Get(val, "length").
        3. -
      3. Assert: len is not an abrupt completion and its value is a positive - integer.
        4. -
      4. Repeat while I < len, -
          -
        1. Let newElement be the result of calling the abstract operation Walk, passing val and ToString(I).
          2. -
        2. If newElement is undefined, then -
            -
          1. Let status be the result of calling the [[Delete]] internal method of val with ToString(I) as the argument.
            2. -
          -
          3. -
        3. Else -
            -
          1. Let status be the result of calling the [[DefineOwnProperty]] internal method of val - with arguments ToString(I) and PropertyDescriptor{[[Value]]: - newElement, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: - true}.
            2. -
          2. NOTE This algorithm intentionally does not throw an exception if status is false.
            3. -
          -
          4. -
        4. ReturnIfAbrupt(status).
          5. -
        5. Add 1 to I.
          6. -
        -
        5. -
      -
      2. -
    2. Else -
        -
      1. Let keys be a List of String values consisting - of the names of all the own properties of val whose [[Enumerable]] attribute is true. The - ordering of the Strings is the same as that used by the Object.keys - standard built-in function.
        2. -
      2. For each String P in keys do, -
          -
        1. Let newElement be the result of calling the abstract operation Walk, passing val and - P.
          2. -
        2. If newElement is undefined, then -
            -
          1. Let status be the result of calling the [[Delete]] internal method of val with - P as the argument.
            2. -
          -
          3. -
        3. Else -
            -
          1. Let status be the result of calling the [[DefineOwnProperty]] internal method of val - with arguments P and PropertyDescriptor{[[Value]]: newElement, [[Writable]]: - true, [[Enumerable]]: true, [[Configurable]]: true}.
            2. -
          2. NOTE This algorithm intentionally does not throw an exception if status is false.
            3. -
          -
          4. -
        4. ReturnIfAbrupt(status).
          5. -
        -
        3. -
      -
      3. -
    -
    4. -
  4. Return the result of calling the [[Call]] internal method of reviver passing holder as - thisArgument and with a List containing name and - val as argumentsList.
    5. -
- -

It is not permitted for a conforming implementation of JSON.parse to extend - the JSON grammars. If an implementation wishes to support a modified or extended JSON interchange format it must do so by - defining a different parse function.

- -
-

NOTE In the case where there are duplicate name Strings within an object, lexically preceding - values for the same key shall be overwritten.

-
-
-
- -
-
-

24.3.2 - JSON.stringify ( value [ , replacer [ , space ] ] )

- -

The stringify function returns a String in UTF-16 encoded JSON format representing an ECMAScript value. It - can take three parameters. The value parameter is an ECMAScript value, which is usually an object or array, - although it can also be a String, Boolean, Number or null. The optional replacer parameter is either a - function that alters the way objects and arrays are stringified, or an array of Strings and Numbers that acts as a white - list for selecting the object properties that will be stringified. The optional space parameter is a String or - Number that allows the result to have white space injected into it to improve human readability.

- -

These are the steps in stringifying an object:

- -
    -
  1. Let stack be an empty List.
    2. -
  2. Let indent be the empty String.
    3. -
  3. Let PropertyList and ReplacerFunction be undefined.
    4. -
  4. If Type(replacer) is Object, then -
      -
    1. If IsCallable(replacer) is true, then -
        -
      1. Let ReplacerFunction be replacer.
        2. -
      -
      2. -
    2. Else if replacer is an exotic Array object, then -
        -
      1. Let PropertyList be an empty List
        2. -
      2. For each value v of a property of replacer that has an array index property name. The - properties are enumerated in the ascending array index order of their names. -
          -
        1. Let item be undefined.
          2. -
        2. If Type(v) is String then let item be - v.
          3. -
        3. Else if Type(v) is Number then let - item be ToString(v).
          4. -
        4. Else if Type(v) is Object then, -
            -
          1. If v has a [[StringData]] or [[NumberData]] internal slot, then let item be ToString(v).
            2. -
          -
          5. -
        5. If item is not undefined and item is not currently an element of - PropertyList then, -
            -
          1. Append item to the end of PropertyList.
            2. -
          -
          6. -
        -
        3. -
      -
      3. -
    -
    5. -
  5. If Type(space) is Object then, -
      -
    1. If space has a [[NumberData]] internal slot - then, -
        -
      1. Let space be ToNumber(space).
        2. -
      -
      2. -
    2. Else if space has a [[StringData]] internal - slot then, -
        -
      1. Let space be ToString(space).
        2. -
      -
      3. -
    -
    6. -
  6. If Type(space) is Number -
      -
    1. Let space be min(10, ToInteger(space)).
      2. -
    2. Set gap to a String containing space occurrences of code unit 0x0020 (the Unicode space - character). This will be the empty String if space is less than 1.
      3. -
    -
    7. -
  7. Else if Type(space) is String -
      -
    1. If the number of elements in space is 10 or less, set gap to space otherwise set gap - to a String consisting of the first 10 elements of space.
      2. -
    -
    8. -
  8. Else -
      -
    1. Set gap to the empty String.
      2. -
    -
    9. -
  9. Let wrapper be ObjectCreate(%ObjectPrototype%).
    10. -
  10. Let status be the result of CreateDataProperty(wrapper, the - empty String, value).
    11. -
  11. Assert: status is true.
    12. -
  12. Return the result of calling the abstract operation Str(the empty String, wrapper).
    13. -
- -
-

NOTE 1 JSON structures are allowed to be nested to any depth, but they must be acyclic. If - value is or contains a cyclic structure, then the stringify function must throw a TypeError exception. - This is an example of a value that cannot be stringified:

- - 
a = [];
- 
a[0] = a;
- 
my_text = JSON.stringify(a); // This must throw a TypeError.
-
- -
-

NOTE 2 Symbolic primitive values are rendered as follows:

- -
    -
  • The null value is rendered in JSON text as the String null.
    • -
  • The undefined value is not rendered.
    • -
  • The true value is rendered in JSON text as the String true.
    • -
  • The false value is rendered in JSON text as the String false.
    • -
-
- -
-

NOTE 3 String values are wrapped in double quotes. The characters " and - \ are escaped with \ prefixes. Control characters are replaced with escape sequences - \uHHHH, or with the shorter forms, \b (backspace), \f (formfeed), \n - (newline), \r (carriage return), \t (tab).

-
- -
-

NOTE 4 Finite numbers are stringified as if by calling ToString(number). NaN and Infinity regardless of sign are - represented as the String null.

-
- -
-

NOTE 5 Values that do not have a JSON representation (such as undefined and functions) - do not produce a String. Instead they produce the undefined value. In arrays these values are represented as the - String null. In objects an unrepresentable value causes the property to be excluded from - stringification.

-
- -
-

NOTE 6 An object is rendered as an opening left brace followed by zero or more properties, - separated with commas, closed with a right brace. A property is a quoted String representing the key or property name, a - colon, and then the stringified property value. An array is rendered as an opening left bracket followed by zero or more - values, separated with commas, closed with a right bracket.

-
-
- -
-

24.3.2.1 Runtime Semantics: Str Abstract Operation

- -

The abstract operation Str(key, holder) has access to - ReplacerFunction from the invocation of the stringify method. Its algorithm is as - follows:

- -
    -
  1. Let value be the result of Get(holder, key).
    2. -
  2. ReturnIfAbrupt(value).
    3. -
  3. If Type(value) is Object, then -
      -
    1. Let toJSON be the result of Get(value, "toJSON").
      2. -
    2. If IsCallable(toJSON) is true -
        -
      1. Let value be the result of calling the [[Call]] internal method of toJSON passing value - as thisArgument and a List containing - key as argumentsList.
        2. -
      2. ReturnIfAbrupt(value).
        3. -
      -
      3. -
    -
    4. -
  4. If ReplacerFunction is not undefined, then -
      -
    1. Let value be the result of calling the [[Call]] internal method of ReplacerFunction passing - holder as the this value and with an argument list consisting of key and value.
      2. -
    2. ReturnIfAbrupt(value).
      3. -
    -
    5. -
  5. If Type(value) is Object then, -
      -
    1. If value has a [[NumberData]] internal slot - then, -
        -
      1. Let value be ToNumber(value).
        2. -
      -
      2. -
    2. Else if value has a [[StringData]] internal - slot then, -
        -
      1. Let value be ToString(value).
        2. -
      -
      3. -
    3. Else if value has a [[BooleanData]] internal - slot then, -
        -
      1. Let value be the value of the [[BooleanData]] internal slot of value.
        2. -
      2. If value is undefined, then throw a TypeError exception.
        3. -
      -
      4. -
    -
    6. -
  6. If value is null then return "null".
    7. -
  7. If value is true then return "true".
    8. -
  8. If value is false then return "false".
    9. -
  9. If Type(value) is String, then return the result of - calling the abstract operation Quote with argument value.
    10. -
  10. If Type(value) is Number -
      -
    1. If value is finite then return ToString(value).
      2. -
    2. Else, return "null".
      3. -
    -
    11. -
  11. If Type(value) is Object, and IsCallable(value) is false -
      -
    1. If value is an exotic Array object then -
        -
      1. Return the result of calling the abstract operation JA with argument value.
        2. -
      -
      2. -
    2. Else, return the result of calling the abstract operation JO with argument value.
      3. -
    -
    12. -
  12. Return undefined.
    13. -
-
- -
-

24.3.2.2 Runtime - Semantics: Quote Abstract Operation

- -

The abstract operation Quote(value) wraps a String value in - double quotes and escapes characters within it.

- -
    -
  1. Let product be code unit 0x0022 (the Unicode double quote character).
    2. -
  2. For each code unit C in value -
      -
    1. If C is 0x0022 or 0x005C (the Unicode reverse solidus character) -
        -
      1. Let product be the concatenation of product and code unit 0x005C.
        2. -
      2. Let product be the concatenation of product and C.
        3. -
      -
      2. -
    2. Else if C is backspace, formfeed, newline, carriage return, or tab -
        -
      1. Let product be the concatenation of product and code unit 0x005C (the Unicode backslash - character).
        2. -
      2. Let abbrev be the string value corresponding to the value of C as follows: - - - - - - - - - - - - - - - - - - - - - -
        backspace"b"
        formfeed"f"
        newline"n"
        carriage return"r"
        tab"t"
        -
        3. -
      3. Let product be the concatenation of product and abbrev.
        4. -
      -
      3. -
    3. Else if C has a code unit value less than 0x0020 (the Unicode space character) -
        -
      1. Let product be the concatenation of product and code unit 0x005C (the Unicode backslash - character).
        2. -
      2. Let product be the concatenation of product and "u".
        3. -
      3. Let hex be the string result of converting the numeric code unit value of C to a String of - four hexadecimal digits. Alphabetic hexadecimal digits are presented as lowercase characters.
        4. -
      4. Let product be the concatenation of product and hex.
        5. -
      -
      4. -
    4. Else -
        -
      1. Let product be the concatenation of product and C.
        2. -
      -
      5. -
    -
    3. -
  3. Let product be the concatenation of product and code unit 0x0022 (the Unicode double quote - character).
    4. -
  4. Return product.
    5. -
-
- -
-

24.3.2.3 Runtime Semantics: JO Abstract Operation

- -

The abstract operation JO(value) serializes an object. It has - access to the stack, indent, gap, and PropertyList of the - invocation of the stringify method.

- -
    -
  1. If stack contains value then throw a TypeError exception because the structure is - cyclical.
    2. -
  2. Append value to stack.
    3. -
  3. Let stepback be indent.
    4. -
  4. Let indent be the concatenation of indent and gap.
    5. -
  5. If PropertyList is not undefined, then -
      -
    1. Let K be PropertyList.
      2. -
    -
    6. -
  6. Else -
      -
    1. Let K be a List of Strings consisting of the keys - of all the own properties of value whose [[Enumerable]] attribute is true and whose property key is a String value. The ordering of the Strings is the same as that used - by the Object.keys standard built-in function.
      2. -
    -
    7. -
  7. Let partial be an empty List.
    8. -
  8. For each element P of K, -
      -
    1. Let strP be the result of Str(P, value).
      2. -
    2. ReturnIfAbrupt(strP).
      3. -
    3. If strP is not undefined -
        -
      1. Let member be the result of calling the abstract operation Quote with - argument P.
        2. -
      2. Let member be the concatenation of member and the string ":".
        3. -
      3. If gap is not the empty String -
          -
        1. Let member be the concatenation of member and code unit 0x0020 (the Unicode space - character).
          2. -
        -
        4. -
      4. Let member be the concatenation of member and strP.
        5. -
      5. Append member to partial.
        6. -
      -
      4. -
    -
    9. -
  9. If partial is empty, then -
      -
    1. Let final be "{}".
      2. -
    -
    10. -
  10. Else -
      -
    1. If gap is the empty String -
        -
      1. Let properties be a String formed by concatenating all the element Strings of partial with - each adjacent pair of Strings separated with code unit 0x002C (the Unicode comma character). A comma is not - inserted either before the first String or after the last String.
        2. -
      2. Let final be the result of concatenating "{", properties, and - "}".
        3. -
      -
      2. -
    2. Else gap is not the empty String -
        -
      1. Let separator be the result of concatenating code unit 0x002C (the comma character), code unit 0x000A - (the line feed character), and indent.
        2. -
      2. Let properties be a String formed by concatenating all the element Strings of partial with - each adjacent pair of Strings separated with separator. The separator String is not inserted - either before the first String or after the last String.
        3. -
      3. Let final be the result of concatenating "{", code unit 0x000A (the line feed - character), indent, properties, code unit 0x000A, stepback, and "}".
        4. -
      -
      3. -
    -
    11. -
  11. Remove the last element of stack.
    12. -
  12. Let indent be stepback.
    13. -
  13. Return final.
    14. -
-
- -
-

24.3.2.4 Runtime Semantics: JA Abstract Operation

- -

The abstract operation JA(value) serializes an array. It has - access to the stack, indent, and gap of the invocation of the stringify method. The - representation of arrays includes only the elements between zero and array.length – 1 inclusive. Properties whose keys are not array indexes are excluded from the - stringification. An array is stringified as an open left bracket, elements separated by comma, and a closing right - bracket.

- -
    -
  1. If stack contains value then throw a TypeError exception because the structure is - cyclical.
    2. -
  2. Append value to stack.
    3. -
  3. Let stepback be indent.
    4. -
  4. Let indent be the concatenation of indent and gap.
    5. -
  5. Let partial be an empty List.
    6. -
  6. Assert: value is a standard array object and hence its - "length" property is a nonnegative integer.
    7. -
  7. Let lenVal be the result of Get(value, "length")
    8. -
  8. Let len be ToLength(lenVal).
    9. -
  9. ReturnIfAbrupt(len).
    10. -
  10. Let index be 0.
    11. -
  11. Repeat while index < len -
      -
    1. Let strP be the result of calling the abstract operation Str(ToString(index), value).
      2. -
    2. ReturnIfAbrupt(strP).
      3. -
    3. If strP is undefined -
        -
      1. Append "null" to partial.
        2. -
      -
      4. -
    4. Else -
        -
      1. Append strP to partial.
        2. -
      -
      5. -
    5. Increment index by 1.
      6. -
    -
    12. -
  12. If partial is empty, then -
      -
    1. Let final be "[]".
      2. -
    -
    13. -
  13. Else -
      -
    1. If gap is the empty String -
        -
      1. Let properties be a String formed by concatenating all the element Strings of partial with - each adjacent pair of Strings separated with code unit 0x002C (the comma character). A comma is not inserted - either before the first String or after the last String.
        2. -
      2. Let final be the result of concatenating "[", properties, and - "]".
        3. -
      -
      2. -
    2. Else -
        -
      1. Let separator be the result of concatenating code unit 0x002C (the comma character), code unit 0x000A - (the line feed character), and indent.
        2. -
      2. Let properties be a String formed by concatenating all the element Strings of partial with - each adjacent pair of Strings separated with separator. The separator String is not inserted - either before the first String or after the last String.
        3. -
      3. Let final be the result of concatenating "[", code unit 0x000A (the line feed - character), indent, properties, code unit 0x000A, stepback, and "]".
        4. -
      -
      3. -
    -
    14. -
  14. Remove the last element of stack.
    15. -
  15. Let indent be stepback.
    16. -
  16. Return final.
    17. -
-
-
- -
-

24.3.3 - JSON [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "JSON".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
-
- -
-
-

25 - Control Abstraction Objects

-
- -
-
-

25.1 Common Iteration Interfaces

- -

An interface is a set of property keys whose associated values match a specific specification. Any object that provides - all the properties as described by an interface’s specification conforms to that interface. An interface is not - represented by an distinct object. There may be many separately implemented objects that conform to any interface. An - individual object may conform to multiple interfaces.

-
- -
-

25.1.1 - The Iterable Interface

- -

The Iterable interface includes the following property:

- -
- - - - - - - - - - - -
PropertyValueRequirements
@@iteratorA zero arguments function that returns an object.The function returns an object that conforms to the iterator interface.
-
-
- -
-

25.1.2 - The Iterator Interface

- -

The Iterator interface includes the following properties:

- -
- - - - - - - - - - - -
PropertyValueRequirements
nextA function that returns an object.The function returns an object that conforms to the IteratorResult interface. If a previous call to the next method of an Iterator has returned an IteratorResult object whose done property is true, then all subsequent calls to the next method of that object must also return an IteratorResult object whose done property is true,
-
- -
-

NOTE Arguments may be passed to the next function but their interpretation and validity is - dependent upon the target Iterator. The for-of statement and other common users of Iterators do not pass any arguments, so - Iterators that expect to be used in such a manner must be prepared to deal with being called with no arguments.

-
-
- -
-

25.1.3 The IteratorResult Interface

- -

The IteratorResult interface includes the following properties:

- -
- - - - - - - - - - - - - - - - -
PropertyValueRequirements
doneEither true or false.This is the result status of an iterator next method call. If the end of the iterator was reached done is true. If the end was not reached done is false and a value is available. If a done property (either own or inherited does not exist), it is consider to have the value false.
valueAny ECMAScript languge value.If done is false, this is the current iteration element value. If done is true, this is the return value of the iterator, if it supplied one. If the iterator does not have a return value, value is undefined. In that case, the value property may be absent from the conforming object if it does not inherit an explicit value property.
-
-
-
- -
-
-

25.2 - GeneratorFunction Objects

- -

Generator Function objects are constructor functions that are usually created by evaluating GeneratorDeclaration, GeneratorExpression, and GeneratorMethod syntactic productions. They may also be created by calling the - GeneratorFunction constructor.

- -
- A staggering variety of boxes and arrows. -
Figure 2 (Informative) — Generator Objects Relationships
-
-
- -
-
-

25.2.1 The GeneratorFunction Constructor

- -

The GeneratorFunction constructor is the %GeneratorFunction% intrinsic. When GeneratorFunction is called - as a function rather than as a constructor, it creates and initializes a new GeneratorFunction object. Thus the function - call GeneratorFunction (…) is equivalent to the object creation expression - new GeneratorFunction (…) with the same arguments. However, if the - this value passed in the call is an Object with a [[Code]] internal slot whose value is undefined, it initializes the this value using the argument values. This permits - GeneratorFunction to be used both as factory method and to perform constructor instance initialization.

- -

GeneratorFunction may be subclassed and subclass constructors may perform a super invocation - of the GeneratorFunction constructor to initialize subclass instances. However, all syntactic forms for - defining generator function objects create direct instances of GeneratorFunction. There is no syntactic means - to create instances of GeneratorFunction subclasses.

-
- -
-

25.2.1.1 GeneratorFunction (p1, p2, … , pn, body)

- -

The last argument specifies the body (executable code) of a generator function; any preceding arguments specify formal - parameters.

- -

When the GeneratorFunction function is called with some arguments p1, p2, … , - pn, body (where n might be 0, that is, - there are no “p” arguments, and where body might also not be provided), the following - steps are taken:

- -
    -
  1. Let argCount be the total number of arguments passed to this function invocation.
    2. -
  2. Let P be the empty String.
    3. -
  3. If argCount = 0, let bodyText be the empty String.
    4. -
  4. Else if argCount = 1, let bodyText be that argument.
    5. -
  5. Else argCount > 1, -
      -
    1. Let firstArg be the first argument.
      2. -
    2. Let P be ToString(firstArg).
      3. -
    3. ReturnIfAbrupt(P).
      4. -
    4. Let k be 2.
      5. -
    5. Repeat, while k < argCount -
        -
      1. Let nextArg be the k’th argument.
        2. -
      2. Let nextArgString be ToString(nextArg).
        3. -
      3. ReturnIfAbrupt(nextArgString).
        4. -
      4. Let P be the result of concatenating the previous value of P, the String "," (a - comma), and nextArgString.
        5. -
      5. Increase k by 1.
        6. -
      -
      6. -
    6. Let bodyText be the k’th argument.
      7. -
    -
    6. -
  6. Let bodyText be ToString(bodyText).
    7. -
  7. ReturnIfAbrupt(bodyText).
    8. -
  8. Let parameters be the result of parsing P, interpreted as UTF-16 encoded Unicode text as described in - 10.1.1, using FormalParameters as the goal symbol. - Throw a SyntaxError exception if the parse fails.
    9. -
  9. Let funcBody be the result of parsing bodyText, interpreted as UTF-16 encoded Unicode text as - described in 10.1.1, using - FunctionBody[Yield] as the goal symbol. Throw a SyntaxError exception if the parse fails or - if any static semantics errors are detected.
    10. -
  10. If IsSimpleParameterList of parameters is false and any element of the BoundNames of parameters - also occurs in the VarDeclaredNames of funcBody, then throw a SyntaxError exception.
    11. -
  11. If any element of the BoundNames of parameters also occurs in the LexicallyDeclaredNames of funcBody, - then throw a SyntaxError exception.
    12. -
  12. If bodyText is strict mode code (see - 10.2.1) then let strict be true, else let strict be false.
    13. -
  13. Let scope be the Global Environment.
    14. -
  14. Let F be the this value.
    15. -
  15. If Type(F) is not Object or if F does not have a - [[Code]] internal slot or if the value of [[Code]] is - not undefined, then -
      -
    1. Let C be the function that is currently being evaluated.
      2. -
    2. Let proto be the result of GetPrototypeFromConstructor(C, - "%Generator%").
      3. -
    3. ReturnIfAbrupt(proto).
      4. -
    4. Let F be FunctionAllocate(proto , strict, - "generator").
      5. -
    5. ReturnIfAbrupt(F)..
      6. -
    -
    16. -
  16. Let isExtensible be IsExtensible(F).
    17. -
  17. ReturnIfAbrupt(isExtensible).
    18. -
  18. If isExtensible is false, then throw a TypeError exception.
    19. -
  19. If the value of F’s [[FunctionKind]] internal - slot is not "generator", then throw a TypeError exception.
    20. -
  20. Using funcBody as the FunctionBody production, let body be the supplemental syntactic grammar - production: GeneratorBody : FunctionBody .
    21. -
  21. Let status be FunctionInitialize(F, Normal, strict, parameters, body, scope).
    22. -
  22. Let prototype ObjectCreate(%GeneratorPrototype%).
    23. -
  23. If ReferencesSuper(funcBody) is true or ReferencesSuper(parameters) is true, then -
      -
    1. Perform MakeMethod(F, undefined, undefined).
      2. -
    -
    24. -
  24. Let status be the result of the abstract operation MakeConstructor with - arguments F, true, and prototype.
    25. -
  25. ReturnIfAbrupt(status).
    26. -
  26. Let hasName be HasOwnProperty(F, "name").
    27. -
  27. ReturnIfAbrupt(hasName).
    28. -
  28. If hasName is false, then perform SetFunctionName(F, - "anonymous").
    29. -
  29. Return F.
    30. -
- -

A prototype property is automatically created for every function created using the - GeneratorFunction constructor, to provide for the possibility that the function will be used as a - constructor.

-
- -
-

25.2.1.2 new GeneratorFunction ( ... argumentsList)

- -

When GeneratorFunction is called as part of a new expression, it creates and initializes a - newly created object:

- -
    -
  1. Let F be the GeneratorFunction function object on which the new operator was - applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct (F, argumentsList).
    4. -
- -

If GeneratorFunction is implemented as an ECMAScript function - object, its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

25.2.2 Properties of the GeneratorFunction Constructor

- -

The GeneratorFunction constructor is a built-in Function object that inherits from the Function constructor. The value - of the [[Prototype]] internal slot of the GeneratorFunction - constructor is the intrinsic object %Function%.

- -

The value of the [[Extensible]] internal slot of the - GeneratorFunction constructor is true.

- -

The value of the name property of the GeneratorFunction is "GeneratorFunction".

- -

The GeneratorFunction constructor has the following properties:

-
- -
-

25.2.2.1 GeneratorFunction.length

- -

This is a data property with a value of 1. This property has the attributes { [[Writable]]: false, - [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

25.2.2.2 GeneratorFunction.prototype

- -

The initial value of GeneratorFunction.prototype is %Generator%, the standard built-in GeneratorFunction - prototype.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

25.2.2.3 GeneratorFunction[ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let proto be the result of GetPrototypeFromConstructor(F, "%Generator%").
    3. -
  3. ReturnIfAbrupt(proto).
    4. -
  4. Return FunctionAllocate(proto, false, - "generator").
    5. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE The GeneratorFunction @@create function passes false as the - strict parameter to FunctionAllocate. This causes the allocated ECMAScript function object to have the internal methods of a non-strict - function. The GeneratorFunction constructor may reset the functions [[Strict]] internal slot to true. It is up to the implementation - whether this also changes the internal methods.

-
-
-
- -
-
-

25.2.3 Properties of the GeneratorFunction Prototype Object

- -

The GeneratorFunction prototype object is an ordinary object. It is not a function object and does not have a [[Code]] - internal slot or any other of the internal slots listed in - Table 26 or Table 47. In addition to being the value of the prototype - property of the %GeneratorFunction% intrinsic and is itself the %Generator% intrinsic.

- -

The value of the [[Prototype]] internal slot of the - GeneratorFunction prototype object is the %FunctionPrototype% intrinsic object. The initial value of the [[Extensible]] internal slot of the GeneratorFunction prototype object is - true.

-
- -
-

25.2.3.1 GeneratorFunction.prototype.constructor

- -

The initial value of GeneratorFunction.prototype.constructor is the intrinsic object - %GeneratorFunction%.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

25.2.3.2 GeneratorFunction.prototype.prototype

- -

The value of GeneratorFunction.prototype.prototype is the %GeneratorPrototype% intrinsic object.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

25.2.3.3 GeneratorFunction.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "GeneratorFunction".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

25.2.3.4 GeneratorFunction.prototype [ @@create ] ( )

- -

The @@create method of an object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%GeneratorPrototype%", ( [[GeneratorState]], [[GeneratorContext]]) ).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-
-

25.2.4 GeneratorFunction Instances

- -

Every GeneratorFunction instance is an ECMAScript function object and - has the internal slots listed in Table 26. The value of the [[FunctionKind]] internal slot for all such instances is - "generator".

- -

The GeneratorFunction instances have the following own properties:

-
- -
-

25.2.4.1 length

- -

The value of the length property is an integer that indicates the typical number of arguments expected by - the GeneratorFunction. However, the language permits the function to be invoked with some other number of arguments. The - behaviour of a GeneratorFunction when invoked on a number of arguments other than the number specified by its - length property depends on the function.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
- -
-

25.2.4.2 prototype

- -

Whenever a GeneratorFunction instance is created another ordinary object is also created and is the initial value of - the generator function’s prototype property. The value of the prototype property is used to initialize - the [[Prototype]] internal slot of a newly created Generator - object before the generator function object is invoked as a constructor for that newly created object.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

- -
-

NOTE Unlike function instances, the object that is the value of the a - GeneratorFunction’s prototype property does not have a constructor property whose value - is the GeneratorFunction instance.

-
-
-
-
- -
-
-

25.3 - Generator Objects

- -

A Generator object is an instance of a generator function and conforms to both the Iterator and Iterable - interfaces.

- -

Generator instances directly inherit properties from the object that is the value of the prototype property - of the Generator function that created the instance. Generator instances indirectly inherit properties from the Generator - Prototype intrinsic, %GeneratorPrototype%.

-
- -
-
-

25.3.1 Properties of Generator Prototype

- -

The Generator prototype object is the %GeneratorPrototype% intrinsic. It is also the initial value of the - prototype property of the %Generator% intrinsic (the GeneratorFrunction.prototype).

- -

The Generator prototype is an ordinary object. It is not a Generator instance and does not have a [[GeneratorState]] internal slot.

- -

The value of the [[Prototype]] internal slot of the - Generator prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The initial value of the [[Extensible]] internal slot of the Function prototype object is - true.

- -

All Generator instances indirectly inherit properties of the Generator prototype object.

-
- -
-

25.3.1.1 Generator.prototype.constructor

- -

The initial value of Generator.prototype.constructor is the intrinsic object %Generator%.

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-

25.3.1.2 Generator.prototype.next ( value )

- -

The next method performs the following steps:

- -
    -
  1. Let g be the this value.
    2. -
  2. Return the result of GeneratorResume(g, value).
    3. -
-
- -
-

25.3.1.3 Generator.prototype.throw ( exception )

- -

The throw method performs the following steps:

- -
    -
  1. Let generator be the this value.
    2. -
  2. If Type(generator) is not Object, then throw a - TypeError exception.
    3. -
  3. If generator does not have a [[GeneratorState]] internal slot, then throw a TypeError - exception.
    4. -
  4. Let state be the value of generator’s [[GeneratorState]] internal slot.
    5. -
  5. Assert: generator also has a [[GeneratorContext]] internal slot.
    6. -
  6. Let E be Completion{[[type]]: throw, [[value]]: exception, [[target]]: empty}.
    7. -
  7. If state is "completed", then return E.
    8. -
  8. If state is neither "suspendedStart" nor "suspendedYield", then throw a - TypeError exception.
    9. -
  9. If state is "suspendedStart" then, -
      -
    1. Set generator’s [[GeneratorState]] internal slot to "completed".
      2. -
    2. Once a generator enters the "completed" state it never leaves it and its associated execution context is never resumed. Any execution state associated with - generator can be discard at this point.
      3. -
    3. Return E.
      4. -
    -
    10. -
  10. Let genContext be the value of generator’s [[GeneratorContext]] internal slot.
    11. -
  11. Let methodContext be the running execution context.
    12. -
  12. Suspend methodContext.
    13. -
  13. Set generator’s [[GeneratorState]] internal - slot to "executing".
    14. -
  14. Push genContext onto the execution context stack; genContext is - now the running execution context.
    15. -
  15. Resume the suspended evaluation of genContext using E as the - result of the operation that suspended it. Let result be the value - returned by the resumed compation.
    16. -
  16. Assert: When we return here, genContext has already been removed - from the execution context stack and methodContext is the currently running execution context.
    17. -
  17. Return result.
    18. -
-
- -
-

25.3.1.4 Generator.prototype [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

25.3.1.5 Generator.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Generator".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

25.3.2 Properties of Generator Instances

- -

Generator instances are initially created with the internal slots described in Table 47.

- -
-
Table 47 — Internal Slots of Generator Instances
- - - - - - - - - - - - - -
Internal SlotDescription
[[GeneratorState]]The current execution state of the generator. The possible values are: undefined, "suspendedStart", "suspendedYield", "executing", and "completed".
[[GeneratorContext]]The execution context that is used when executing the code of this generator.
-
-
- -
-
-

25.3.3 Generator Abstract Operations

-
- -
-

25.3.3.1 - GeneratorStart (generator, generatorBody)

- -

The abstract operation GeneratorStart with arguments generator and - generatorBody performs the following steps:

- -
    -
  1. Assert: The value of generator’s [[GeneratorState]] internal slot is undefined.
    2. -
  2. Let genContext be the running execution context.
    3. -
  3. Set the Generator component of genContext to generator.
    4. -
  4. Set the code evaluation state of genContext such that when evaluation is resumed for that execution context the following steps will be performed: -
      -
    1. Let result be the result of evaluating generatorBody.
      2. -
    2. Assert: If we return here, the generator either threw an exception or - performed either an implicit or explicit return.
      3. -
    3. Remove genContext from the execution context stack and restore the - execution context that is at the top of the execution context stack as the running - execution context.
      4. -
    4. Set generator’s [[GeneratorState]] internal slot to "completed".
      5. -
    5. Once a generator enters the "completed" state it never leaves it and its associated execution context is never resumed. Any execution state associated with - generator can be discard at this point.
      6. -
    6. ReturnIfAbrupt(result).
      7. -
    7. Return CreateIterResultObject(result, true).
      8. -
    -
    5. -
  5. Set generator’s [[GeneratorContext]] internal - slot to genContext.
    6. -
  6. Set generator’s [[GeneratorState]] internal - slot to "suspendedStart".
    7. -
  7. Return NormalCompletion(generator).
    8. -
-
- -
-

25.3.3.2 - GeneratorResume ( generator, value )

- -

The abstract operation GeneratorResume with arguments generator and - value performs the following steps:

- -
    -
  1. If Type(generator) is not Object, then throw a - TypeError exception.
    2. -
  2. If generator does not have a [[GeneratorState]] internal slot, then throw a TypeError - exception.
    3. -
  3. Let state be the value of generator’s [[GeneratorState]] internal slot.
    4. -
  4. Assert: generator also has a [[GeneratorContext]] internal slot.
    5. -
  5. If state is "completed", then return CreateIterResultObject(undefined, true).
    6. -
  6. If state is neither "suspendedStart" nor "suspendedYield", then throw a - TypeError exception.
    7. -
  7. Let genContext be the value of generator’s [[GeneratorContext]] internal slot.
    8. -
  8. Let methodContext be the running execution context.
    9. -
  9. Suspend methodContext.
    10. -
  10. Set generator’s [[GeneratorState]] internal - slot to "executing".
    11. -
  11. Push genContext onto the execution context stack; genContext is - now the running execution context.
    12. -
  12. Resume the suspended evaluation of genContext using NormalCompletion(value) as the result of the operation that suspended it. Let result be the value returned by the resumed - computation.
    13. -
  13. Assert: When we return here, genContext has already been removed - from the execution context stack and methodContext is the currently running execution context.
    14. -
  14. Return result.
    15. -
-
- -
-

25.3.3.3 - GeneratorYield ( iterNextObj )

- -

The abstract operation GeneratorYield with argument iterNextObj performs the following steps:

- -
    -
  1. Assert: iterNextObj is an Object that implemented the - IteratorResult interface.
    2. -
  2. Let genContext be the running execution context.
    3. -
  3. Assert: genContext is the execution context of a generator.
    4. -
  4. Let generator be the value of the Generator component of genContext.
    5. -
  5. Set the value of generator’s [[GeneratorState]] internal slot to "suspendedYield".
    6. -
  6. Remove genContext from the execution context stack and restore the execution context that is at the top of the - execution context stack as the running execution context.
    7. -
  7. Set the code evaluation state of genContext such that when evaluation is resumed with a Completion resumptionValue the following steps will be - performed: -
      -
    1. Return resumptionValue.
      2. -
    2. NOTE: This returns to the evaluation of the YieldExpression production that originally called this - abstract operation.
      3. -
    -
    8. -
  8. Return NormalCompletion(iterNextObj).
    9. -
  9. NOTE: This returns to the evaluation of the operation that had most previously resumed evaluation of - genContext.
    10. -
-
-
-
- -
-
-

25.4 Promise - Objects

- -

A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) - computation.

- -

Any Promise object is in one of three mutually exclusive states: fulfilled, rejected, and - pending:

- -
    -
  • -

    A promise p is fulfilled if p.then(f, r) will immediately enqueue a Task to call the - function f.

    -
    • - -
  • -

    A promise p is rejected if p.then(f, r) will immediately enqueue a Task to call the - function r.

    -
    • - -
  • -

    A promise is pending if it is neither fulfilled nor rejected.

    -
    • -
- -

A promise is said to be settled if it is not pending, i.e. if it is either fulfilled or rejected.

- -

A promise is resolved if it is settled or if it has been "locked in" to match the state of another promise. - Attempting to resolve or reject a resolved promise has no effect. A promise is unresolved if it is not resolved. An - unresolved promise is always in the pending state. A resolved promise may be pending, fulfilled or rejected.

-
- -
-
-

25.4.1 Promise Abstract Operations

-
- -
-
-

25.4.1.1 PromiseCapability Records

- -

A PromiseCapability is a Record value used to encapsulate a promise object along with the functions that are capable - of resolving or rejecting that promise object. PromiseCapability records are produced by the NewPromiseCapability abstract operation.

- -

PromiseCapability Records have the fields listed in Table 48.

- -
-
Table 48 — PromiseCapability Record Fields
- - - - - - - - - - - - - - - - - - - - - -
Field NameValueMeaning
[[Promise]]An objectAn object that is usable as a promise.
[[Resolve]]A function objectThe function that is used to resolve the given promise object.
[[Reject]]A function objectThe function that is used to reject the given promise object.
-
-
- -
-

25.4.1.1.1 IfAbruptRejectPromise ( value, capability )

- -

IfAbruptRejectPromise is a short hand for a sequence of algorithm steps that use a PromiseCapability record. An - algorithm step of the form:

- -
    -
  1. IfAbruptRejectPromise(value, capability).
    2. -
- -

means the same thing as:

- -
    -
  1. If value is an abrupt completion, -
      -
    1. Let rejectResult be the result of calling the [[Call]] internal method of capability.[[Reject]] - with undefined as thisArgument and (value.[[value]]) as argumentsList.
      2. -
    2. ReturnIfAbrupt(rejectResult).
      3. -
    3. Return capability.[[Promise]].
      4. -
    -
    2. -
  2. Else if value is a Completion Record, then let - value be value.[[value]].
    3. -
-
-
- -
-

25.4.1.2 PromiseReaction Records

- -

The PromiseReaction is a Record value used to store information about how a promise should react when it becomes - resolved or rejected with a given value. PromiseReaction records are created by the then method of the - Promise prototype, and are used by a PromiseReactionTask.

- -

PromiseReaction records have the fields listed in Table 49.

- -
-
Table 49 — PromiseReaction Record Fields
- - - - - - - - - - - - - - - - -
Field NameValueMeaning
[[Capabilities]]A PromiseCapability recordThe capabilities of the promise for which this record provides a reaction handler.
[[Handler]]A function object or a StringThe function that should be applied to the incoming value, and whose return value will govern what happens to the derived promise. If [[Handler]] is "Identity" it is equivalent to a function that simply returns its first argument. If [[Handler]] is "Thrower" it is equivalent to a function that throws its first argument as an exception.
-
-
- -
-
-

25.4.1.3 CreateResolvingFunctions ( promise )

- -

When CreateResolvingFunctions is performed with argument promise, the following steps are taken:

- -
    -
  1. Let alreadyResolved be a new Record { [[value]]: false }.
    2. -
  2. Let resolve be a new built-in function object as defined in Promise Resolve Functions (25.4.1.4).
    3. -
  3. Set the [[Promise]] internal slot of resolve - to promise.
    4. -
  4. Set the [[AlreadyResolved]] internal slot of - resolve to alreadyResolved.
    5. -
  5. Let reject be a new built-in function object as defined in Promise Reject Functions (25.4.1.3.1).
    6. -
  6. Set the [[Promise]] internal slot of reject - to promise.
    7. -
  7. Set the [[AlreadyResolved]] internal slot of - reject to alreadyResolved.
    8. -
  8. Return a new Record { [[Resolve]]: resolve, [[Reject]]: reject }.
    9. -
-
- -
-

25.4.1.3.1 Promise Reject Functions

- -

A promise reject function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal - slots.

- -

When a promise reject function F is called with argument reason, the following steps are - taken:

- -
    -
  1. Assert: F has a [[Promise]] internal slot whose value is an Object.
    2. -
  2. Let promise be the value of F's [[Promise]] internal slot.
    3. -
  3. Let alreadyResolved be the value of F's [[AlreadyResolved]] internal slot.
    4. -
  4. If alreadyResolved.[[value]] is true, then return undefined.
    5. -
  5. Set alreadyResolved.[[value]] to true.
    6. -
  6. Return RejectPromise(promise, reason).
    7. -
-
-
- -
-

25.4.1.4 Promise Resolve Functions

- -

A promise resolve function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal - slots.

- -

When a promise resolve function F is called with argument resolution, the following steps are - taken:

- -
    -
  1. Assert: F has a [[Promise]] internal slot whose value is an Object.
    2. -
  2. Let promise be the value of F's [[Promise]] internal slot.
    3. -
  3. Let alreadyResolved be the value of F's [[AlreadyResolved]] internal slot.
    4. -
  4. If alreadyResolved.[[value]] is true, then return undefined.
    5. -
  5. Set alreadyResolved.[[value]] to true.
    6. -
  6. If SameValue(resolution, promise) is true, then -
      -
    1. Let selfResolutionError be a newly-created TypeError object.
      2. -
    2. Return RejectPromise(promise, selfResolutionError).
      3. -
    -
    7. -
  7. If Type(resolution) is not Object, then -
      -
    1. Return FulfillPromise(promise, resolution).
      2. -
    -
    8. -
  8. Let then be Get(resolution, "then").
    9. -
  9. If then is an abrupt completion, then -
      -
    1. Return RejectPromise(promise, then.[[value]]).
      2. -
    -
    10. -
  10. Let then be then.[[value]].
    11. -
  11. If IsCallable(then) is false, then -
      -
    1. Return FulfillPromise(promise, resolution).
      2. -
    -
    12. -
  12. Perform EnqueueTas ("PromiseTasks", PromiseResolveThenableTask, (promise, resolution, - then))
    13. -
  13. Return undefined.
    14. -
-
- -
-

25.4.1.5 - FulfillPromise ( promise, value)

- -

When the FulfillPromise abstract operation is called with arguments promise and value the - following steps are taken:

- -
    -
  1. Assert: the value of promise's [[PromiseState]] internal slot is "pending".
    2. -
  2. Let reactions be the value of promise's [[PromiseFulfillReactions]] internal slot.
    3. -
  3. Set the value of promise's [[PromiseResult]] internal slot to value.
    4. -
  4. Set the value of promise's [[PromiseFulfillReactions]] internal slot to undefined.
    5. -
  5. Set the value of promise's [[PromiseRejectReactions]] internal slot to undefined.
    6. -
  6. Set the value of promise's [[PromiseState]] internal slot to "fulfilled".
    7. -
  7. Return TriggerPromiseReactions(reactions, value).
    8. -
-
- -
-
-

25.4.1.6 NewPromiseCapability ( C )

- -

The abstract operation NewPromiseCapability takes a constructor function, and attempts to use that constructor - function in the fashion of the built-in Promise constructor to create a Promise object and extract its - resolve and reject functions. The promise plus the resolve and reject functions are used to initialize a new - PromiseCapability record which is returned as the value of this abstract operation.

- -
    -
  1. If IsConstructor(C) is false, throw a TypeError - exception.
    2. -
  2. Assert: C is a constructor function that supports the parameter - conventions of the Promise constructor (see 25.4.3.1).
    3. -
  3. Let promise be CreateFromConstructor(C).
    4. -
  4. ReturnIfAbrupt(promise).
    5. -
  5. If Type(promise) is not Object, then throw a - TypeError exception.
    6. -
  6. Return CreatePromiseCapabilityRecord(promise, - C).
    7. -
- -
-

NOTE This abstract operation supports Promise subclassing, as it is generic on any - constructor that calls a passed executor function argument in the same way as the Promise constructor. It is used to - generalize static methods of the Promise constructor to any subclass.

-
-
- -
-

25.4.1.6.1 CreatePromiseCapabilityRecord( promise, constructor )

- -

When the CreatePromiseCapabilityRecord abstract operation is called with arguments promise and - constructor the following steps are taken:

- -
    -
  1. Assert: promise is an uninitialized object created as if by - invoking @@create on constructor.
    2. -
  2. Assert: IsConstructor(constructor) is true.
    3. -
  3. Let promiseCapability be a new PromiseCapability { [[Promise]]: promise, [[Resolve]]: - undefined, [[Reject]]: undefined }.
    4. -
  4. Let executor be a new built-in function object as defined in GetCapabilitiesExecutor Functions (25.4.1.6.1).
    5. -
  5. Set the [[Capability]] internal slot of - executor to promiseCapability.
    6. -
  6. Let constructorResult be the result of calling the [[Call]] internal method of constructor, passing - promise and (executor) as the arguments.
    7. -
  7. ReturnIfAbrupt(constructorResult).
    8. -
  8. If IsCallable(promiseCapability.[[Resolve]]) is false, then throw a - TypeError exception.
    9. -
  9. If IsCallable(promiseCapability.[[Reject]]) is false, then throw a - TypeError exception.
    10. -
  10. If Type(constructorResult) is Object and SameValue(promise, constructorResult) is false, then throw a - TypeError exception.
    11. -
  11. Return promiseCapability.
    12. -
-
- -
-

25.4.1.6.2 GetCapabilitiesExecutor Functions

- -

A GetCapabilitiesExecutor function is an anonymous built-in function that has a [[Capability]] internal slot.

- -

When a GetCapabilitiesExecutor function F is called with arguments resolve and - reject the following steps are taken:

- -
    -
  1. Assert: F has a [[Capability]] internal slot whose value is a PromiseCapability - Record.
    2. -
  2. Let promiseCapability be the value of F's [[Capability]] internal slot.
    3. -
  3. If promiseCapability.[[Resolve]] is not undefined, then throw a TypeError exception.
    4. -
  4. If promiseCapability.[[Reject]] is not undefined, then throw a TypeError exception.
    5. -
  5. Set promiseCapability.[[Resolve]] to resolve.
    6. -
  6. Set promiseCapability.[[Reject]] to reject.
    7. -
  7. Return undefined.
    8. -
-
-
- -
-

25.4.1.7 - IsPromise ( x )

- -

The abstract operation IsPromise checks for the promise brand on an object.

- -
    -
  1. If Type(x) is not Object, return false.
    2. -
  2. If x does not have a [[PromiseState]] internal - slot, return false.
    3. -
  3. If the value of x's [[PromiseState]] internal - slot is undefined, return false.
    4. -
  4. Return true.
    5. -
-
- -
-

25.4.1.8 - RejectPromise ( promise, reason)

- -

When the RejectPromise abstract operation is called with arguments promise and reason the - following steps are taken:

- -
    -
  1. Assert: the value of promise's [[PromiseState]] internal slot is "pending".
    2. -
  2. Let reactions be the value of promise's [[PromiseRejectReactions]] internal slot.
    3. -
  3. Set the value of promise's [[PromiseResult]] internal slot to reason.
    4. -
  4. Set the value of promise's [[PromiseFulfillReactions]] internal slot to undefined.
    5. -
  5. Set the value of promise's [[PromiseRejectReactions]] internal slot to undefined.
    6. -
  6. Set the value of promise's [[PromiseState]] internal slot to "rejected".
    7. -
  7. Return TriggerPromiseReactions(reactions, reason).
    8. -
-
- -
-

25.4.1.9 TriggerPromiseReactions ( reactions, argument )

- -

The abstract operation TriggerPromiseReactions takes a collection of functions to trigger in the next Task, and calls - them, passing each the given argument. Typically, these reactions will modify a previously-returned promise, possibly - calling in to a user-supplied handler before doing so.

- -
    -
  1. Repeat for each reaction in reactions, in original insertion order -
      -
    1. Perform EnqueueTask("PromiseTasks", PromiseReactionTask, (reaction, argument)).
      2. -
    -
    2. -
  2. Return undefined.
    3. -
-
-
- -
-
-

25.4.2 - Promise Tasks

-
- -
-

25.4.2.1 PromiseReactionTask ( reaction, argument )

- -

The task PromiseReactionTask with parameters reaction and argument applies the appropriate - handler to the incoming value, and uses the handler's return value to resolve or reject the derived promise associated - with that handler.

- -
    -
  1. Assert: reaction is a PromiseReaction Record.
    2. -
  2. Let promiseCapability be reaction.[[Capabilities]].
    3. -
  3. Let handler be reaction.[[Handler]].
    4. -
  4. If handler is "Identity", then let handlerResult be NormalCompletion(argument).
    5. -
  5. Else If handler is "Thrower", then let handlerResult be Completion{[[type]]: throw, [[value]]: argument, [[target]]: empty}.
    6. -
  6. Else, let handlerResult be the result of calling the [[Call]] internal method of handler passing - undefined as thisArgument and (argument) as argumentsList.
    7. -
  7. If handlerResult is an abrupt completion, then -
      -
    1. Let status be the result of calling the [[Call]] internal method of promiseCapability.[[Reject]] - passing undefined as thisArgument and (handlerResult.[[value]]) as - argumentsList.
      2. -
    2. NextTask status.
      3. -
    -
    8. -
  8. Let handlerResult be handlerResult.[[value]].
    9. -
  9. Let status be the result of calling the [[Call]] internal method of promiseCapability.[[Resolve]] - passing undefined as thisArgument and (handlerResult) as argumentsList.
    10. -
  10. NextTask status.
    11. -
-
- -
-

25.4.2.2 PromiseResolveThenableTask ( promiseToResolve, thenable, then)

- -

The task PromiseResolveThenableTask with parameters promiseToResolve, thenable, and - then performs the following steps:

- -
    -
  1. Let resolvingFunctions be CreateResolvingFunctions(promise).
    2. -
  2. Let thenCallResult be the result of calling the [[Call]] internal method of then passing - thenable as the thisArgument and (resolvingFunctions.[[Resolve]], - resolvingFunctions.[[Reject]]) as argumentsList.
    3. -
  3. If thenCallResult is an abrupt completion, -
      -
    1. Let status be the result of calling the [[Call]] internal method of resolvingFunctions.[[Reject]] - passing undefined as the thisArgument and (thenCallResult.[[value]]) as - argumentsList.
      2. -
    2. NextTask status.
      3. -
    -
    4. -
  4. NextTask thenCallResult.
    5. -
- -
-

NOTE This Task uses the supplied thenable and its then method to resolve the - given promise. This process must take place as a Task to ensure that the evaluation of the then method - occurs after evaluation of any surrounding code has completed.

-
-
-
- -
-
-

25.4.3 - The Promise Constructor

- -

The Promise constructor is the %Promise% intrinsic object and the initial value of the Promise property of - the global object. When Promise is called as a function rather than as a constructor, it initializes its - this value with the internal state necessary to support the Promise.prototype methods.

- -

The Promise constructor is designed to be subclassable. It may be used as the value in an - extends clause of a class definition. Subclass constructors that intend to inherit the specified - Promise behaviour must include a super call to Promise.

-
- -
-
-

25.4.3.1 - Promise ( executor )

- -

When the Promise function is called with argument executor the following steps are taken:

- -
    -
  1. Let promise be the this value.
    2. -
  2. If Type(promise) is not Object, then throw a - TypeError exception.
    3. -
  3. If promise does not have a [[PromiseState]] internal slot, then throw a TypeError - exception.
    4. -
  4. If promise's [[PromiseState]] internal slot - is not undefined, then throw a TypeError exception.
    5. -
  5. If IsCallable(executor) is false, then throw a TypeError - exception.
    6. -
  6. Return InitializePromise(promise, executor).
    7. -
- -
-

NOTE The executor argument must be a function object. It is called for initiating - and reporting completion of the possibly deferred action represented by this Promise object. The executor is called - with two arguments: resolve and reject. These are functions that may be used by the executor - function to report eventual completion or failure of the deferred computation. Returning from the executor function - does not mean that the deferred action has been completed but only that the request to eventually perform the deferred - action has been accepted.

- -

The resolve function that is passed to an executor function accepts a single argument. The - executor code may eventually call the resolve function to indicate that it wishes to resolve the - associated Promise object. The argument passed to the resolve function represents the eventual value of the - deferred action and can be either the actual fulfillment value or another Promise object which will provide the value - if it is fulfilled.

- -

The reject function that is passed to an executor function accepts a single argument. The - executor code may eventually call the reject function to indicate that the associated Promise is - rejected and will never be fulfilled. The argument passed to the reject function is used as the rejection value - of the promise. Typically it will be an Error object.

-
- -

The resolve and reject functions passed to an executor function by the Promise constructor have the - capability to actually resolve and reject the associated promise. Subclasses may have different constructor behaviour - that passes in customized values for resolve and reject.

-
- -
-

25.4.3.1.1 InitializePromise ( promise, executor )

- -

The abstract operation InitializePromise initializes a newly allocated promise object using an - executor function.

- -
    -
  1. Assert: promise has a [[PromiseState]] internal slot and its value is undefined.
    2. -
  2. Assert: IsCallable(executor) is - true.
    3. -
  3. Set promise's [[PromiseState]] internal slot - to "pending".
    4. -
  4. Set promise's [[PromiseFulfillReactions]] internal slot to a new empty List.
    5. -
  5. Set promise's [[PromiseRejectReactions]] internal - slot to a new empty List.
    6. -
  6. Let resolvingFunctions be CreateResolvingFunctions(promise).
    7. -
  7. Let completion be the result of calling the [[Call]] internal method of executor with - undefined as thisArgument and (resolvingFunctions.[[Resolve]], - resolvingFunctions.[[Reject]]) as argumentsList.
    8. -
  8. If completion is an abrupt completion, then -
      -
    1. Let status be the result of calling the [[Call]] internal method of - resolvingFunctions.[[Reject]] with undefined as thisArgument and - (completion.[[value]]) as argumentsList.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    9. -
  9. Return promise.
    10. -
-
-
- -
-

25.4.3.2 new Promise ( ... argumentsList )

- -

When Promise is called as part of a new expression it is a constructor: it initializes a - newly created object.

- -

Promise called as part of a new expression with argument list argumentsList performs the following - steps:

- -
    -
  1. Let F be the Promise function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return Construct(F, argumentsList).
    4. -
- -

If Promise is implemented as an ECMAScript function object, its - [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

25.4.4 Properties of the Promise Constructor

- -

The value of the [[Prototype]] internal slot of the - Promise constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 1), the Promise constructor has the following properties:

-
- -
-
-

25.4.4.1 - Promise.all ( iterable )

- -

The all function returns a new promise which is fulfilled with an array of fulfillment values for the - passed promises, or rejects with the reason of the first passed promise that rejects. It resoves all elements of the - passed iterable to promises as it runs this algorithm.

- -
    -
  1. Let C be the this value.
    2. -
  2. Let promiseCapability be NewPromiseCapability(C).
    3. -
  3. ReturnIfAbrupt(promiseCapability).
    4. -
  4. Let iterator be GetIterator(iterable).
    5. -
  5. IfAbruptRejectPromise(iterator, promiseCapability).
    6. -
  6. Let values be ArrayCreate(0).
    7. -
  7. Let remainingElementsCount be a new Record { [[value]]: 1 }.
    8. -
  8. Let index be 0.
    9. -
  9. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. IfAbruptRejectPromise(next, promiseCapability).
      3. -
    3. If next is false, -
        -
      1. Set remainingElementsCount.[[value]] to remainingElementsCount.[[value]] - 1.
        2. -
      2. If remainingElementsCount.[[value]] is 0, -
          -
        1. Let resolveResult be the result of calling the [[Call]] internal method of - promiseCapability.[[Resolve]] with undefined as thisArgument and (values) - as argumentsList.
          2. -
        2. ReturnIfAbrupt(resolveResult).
          3. -
        -
        3. -
      3. Return promiseCapability.[[Promise]].
        4. -
      -
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. IfAbruptRejectPromise(nextValue, - promiseCapability).
      6. -
    6. Let nextPromise be Invoke(C, "resolve", - (nextValue)).
      7. -
    7. IfAbruptRejectPromise(nextPromise, - promiseCapability).
      8. -
    8. Let resolveElement be a new built-in function object as defined in Promise.all Resolve Element - Functions.
      9. -
    9. Set the [[AlreadyCalled]] internal slot of - resolveElement to false.
      10. -
    10. Set the [[Index]] internal slot of - resolveElement to index.
      11. -
    11. Set the [[Values]] internal slot of - resolveElement to values.
      12. -
    12. Set the [[Capabilities]] internal slot of - resolveElement to promiseCapability.
      13. -
    13. Set the [[RemainingElements]] internal slot of - resolveElement to remainingElementsCount.
      14. -
    14. Set remainingElementsCount.[[value]] to remainingElementsCount.[[value]] + 1.
      15. -
    15. Let result be Invoke(nextPromise, "then", - (resolveElement, promiseCapability.[[Reject]])).
      16. -
    16. IfAbruptRejectPromise(result, promiseCapability).
      17. -
    17. Set index to index + 1.
      18. -
    -
    10. -
- -

Note: The all function requires its this value to be a constructor function that - supports the parameter conventions of the Promise constructor.

-
- -
-

25.4.4.1.1 Promise.all Resolve Element Functions

- -

A Promise.all resolve element function is an anonymous built-in function that is used - to resolve a specific Promise.all element. Each Promise.all resolve element function has [[Index]], [[Values]], [[Capabilities]], - [[RemainingElements]], and [[AlreadyCalled]] internal slots.

- -

When a Promise.all resolve element function F is called with argument - x, the following steps are taken:

- -
    -
  1. If the value of F's [[AlreadyCalled]] internal - slot is true, then return undefined.
    2. -
  2. Set the value of F's [[AlreadyCalled]] internal - slot to true.
    3. -
  3. Let index be the value of F's [[Index]] internal slot.
    4. -
  4. Let values be the value of F's [[Values]] internal slot.
    5. -
  5. Let promiseCapability be the value of F's [[Capabilities]] internal slot.
    6. -
  6. Let remainingElementsCount be the value of F's [[RemainingElements]] internal slot.
    7. -
  7. Let result be CreateDataProperty(values, ToString(index), x).
    8. -
  8. IfAbruptRejectPromise(result, promiseCapability).
    9. -
  9. Set remainingElementsCount.[[value]] to remainingElementsCount.[[value]] - 1.
    10. -
  10. If remainingElementsCount.[[value]] is 0, -
      -
    1. Return the result of calling the [[Call]] internal method of promiseCapability.[[Resolve]] with - undefined as thisArgument and (values) as argumentsList.
      2. -
    -
    11. -
  11. Return undefined.
    12. -
-
-
- -
-

25.4.4.2 Promise.prototype

- -

The initial value of Promise.prototype is the Promise prototype object (25.4.4.6.1).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

25.4.4.3 - Promise.race ( iterable )

- -

The race function returns a new promise which is settled in the same way as the first passed promise to - settle. It resolves all elements of the passed iterable to promises as - it runs this algorithm.

- -
    -
  1. Let C be the this value.
    2. -
  2. Let promiseCapability be NewPromiseCapability(C).
    3. -
  3. ReturnIfAbrupt(promiseCapability).
    4. -
  4. Let iterator be GetIterator(iterable).
    5. -
  5. IfAbruptRejectPromise(iterator, promiseCapability).
    6. -
  6. Repeat -
      -
    1. Let next be IteratorStep(iterator).
      2. -
    2. IfAbruptRejectPromise(next, promiseCapability).
      3. -
    3. If next is false, return promiseCapability.[[Promise]].
      4. -
    4. Let nextValue be IteratorValue(next).
      5. -
    5. IfAbruptRejectPromise(nextValue, promiseCapability).
      6. -
    6. Let nextPromise be Invoke(C, "resolve", - (nextValue)).
      7. -
    7. IfAbruptRejectPromise(nextPromise, - promiseCapability).
      8. -
    8. Let result be Invoke(nextPromise, "then", - (promiseCapability.[[Resolve]], promiseCapability.[[Reject]])).
      9. -
    9. IfAbruptRejectPromise(result, promiseCapability).
      10. -
    -
    7. -
- -
-

NOTE The race function requires its this value to be a constructor - function that supports the parameter conventions of the Promise constructor. It also requires that its - this value provides a resolve method.

-
-
- -
-

25.4.4.4 - Promise.reject ( r )

- -

The reject function returns a new promise rejected with the passed argument.

- -
    -
  1. Let C be the this value.
    2. -
  2. Let promiseCapability be NewPromiseCapability(C).
    3. -
  3. ReturnIfAbrupt(promiseCapability).
    4. -
  4. Let rejectResult be the result of calling the [[Call]] internal method of promiseCapability.[[Reject]] - with undefined as thisArgument and (r) as argumentsList.
    5. -
  5. ReturnIfAbrupt(rejectResult).
    6. -
  6. Return promiseCapability.[[Promise]].
    7. -
- -
-

NOTE The reject function requires that its this value to be a constructor - function that supports the parameter conventions of the Promise constructor.

-
-
- -
-

25.4.4.5 - Promise.resolve ( x )

- -

The resolve function returns either a new promise resolved with the passed argument, or the argument - itself if the argument a promise produced by this construtor.

- -
    -
  1. Let C be the this value.
    2. -
  2. If IsPromise(x) is true, -
      -
    1. Let constructor be the value of x's [[PromiseConstructor]] internal slot.
      2. -
    2. If SameValue(constructor, C) is true, return x.
      3. -
    -
    3. -
  3. Let promiseCapability be NewPromiseCapability(C).
    4. -
  4. ReturnIfAbrupt(promiseCapability).
    5. -
  5. Let resolveResult be the result of calling the [[Call]] internal method of - promiseCapability.[[Resolve]] with undefined as thisArgument and (x) as - argumentsList.
    6. -
  6. ReturnIfAbrupt(resolveResult).
    7. -
  7. Return promiseCapability.[[Promise]].
    8. -
- -
-

NOTE The resolve function requires that its this value to be a - constructor function that supports the parameter conventions of the Promise constructor.

-
-
- -
-
-

25.4.4.6 Promise [ @@create ] ( )

- -

The @@create method of a Promise function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Return AllocatePromise(F).
    3. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
- -
-

25.4.4.6.1 AllocatePromise ( constructor )

- -

The abstract operation AllocatePromise allocates a new promise object using the constructor argument.

- -
    -
  1. Let obj be OrdinaryCreateFromConstructor(constructor, - "%PromisePrototype%", ([[PromiseState]], [[PromiseConstructor]], [[PromiseResult]], - [[PromiseFulfillReactions]], [[PromiseRejectReactions]]) ).
    2. -
  2. Set the value of obj’s [[PromiseConstructor]] internal slot to constructor.
    3. -
  3. Return obj.
    4. -
-
-
-
- -
-
-

25.4.5 Properties of the Promise Prototype Object

- -

The value of the [[Prototype]] internal slot of the - Promise prototype object is the standard built-in Object prototype object (19.1.3). The Promise prototype object is an ordinary object. It - does not have a [[PromiseState]] internal slot or any of the - other internal slots of Promise instances.

-
- -
-

25.4.5.1 Promise.prototype.catch ( onRejected )

- -

When the catch method is called with argument onRejected the following steps are taken:

- -
    -
  1. Let promise be the this value.
    2. -
  2. Return Invoke(promise, "then", (undefined, - onRejected)).
    3. -
-
- -
-

25.4.5.2 Promise.prototype.constructor

- -

The initial value of Promise.prototype.constructor is the standard built-in Promise constructor.

-
- -
-

25.4.5.3 Promise.prototype.then ( onFulfilled , onRejected )

- -

When the then method is called with arguments onFulfilled and onRejected the - following steps are taken:

- -
    -
  1. Let promise be the this value.
    2. -
  2. If IsPromise(promise) is false, throw a TypeError exception.
    3. -
  3. If IsCallable(onFulfilled) is false, then -
      -
    1. Let onFulfilled be "Identity".
      2. -
    -
    4. -
  4. If IsCallable(onRejected) is false, then -
      -
    1. Let onRejected be "Thrower".
      2. -
    -
    5. -
  5. Let C be Get(promise, "constructor").
    6. -
  6. ReturnIfAbrupt(C).
    7. -
  7. Let promiseCapability be NewPromiseCapability(C).
    8. -
  8. ReturnIfAbrupt(promiseCapability).
    9. -
  9. Let fulfillReaction be the PromiseReaction { [[Capabilities]]: promiseCapability, [[Handler]]: - onFulfilled }.
    10. -
  10. Let rejectReaction be the PromiseReaction { [[Capabilities]]: promiseCapability, [[Handler]]: - onRejected}.
    11. -
  11. If the value of promise's [[PromiseState]] internal - slot is "pending", -
      -
    1. Append fulfillReaction as the last element of the List that is the value of promise's - [[PromiseFulfillReactions]] internal slot.
      2. -
    2. Append rejectReaction as the last element of the List that is the value of promise's - [[PromiseRejectReactions]] internal slot.
      3. -
    -
    12. -
  12. Else if the value of promise's [[PromiseState]] internal slot is "fulfilled", -
      -
    1. Let value be the value of promise's [[PromiseResult]] internal slot.
      2. -
    2. Perform EnqueueTask("PromiseTasks", PromiseReactionTask, (fulfillReaction, value)).
      3. -
    -
    13. -
  13. Else if the value of promise's [[PromiseState]] internal slot is "rejected", -
      -
    1. Let reason be the value of promise's [[PromiseResult]] internal slot.
      2. -
    2. Perform EnqueueTask("PromiseTasks", PromiseReactionTask, (rejectReaction, reason)).
      3. -
    -
    14. -
  14. Return promiseCapability.[[Promise]].
    15. -
-
- -
-

25.4.5.4 Promise.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Promise".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
-
- -
-

25.4.6 Properties of Promise Instances

- -

Promise instances are ordinary objects that inherit properties from the Promise prototype object (the intrinsic, - %PromisePrototype%). Promise instances are initially created with the internal slots described in Table - 50.

- -
-
Table 50 — Internal Slots of Promise Instances
- - - - - - - - - - - - - - - - - - - - - - - - - -
Internal SlotDescription
[[PromiseState]]A string value that governs how a promise will react to incoming calls to its then method. The possible values are: undefined, "pending", "fulfilled", and "rejected".
[[PromiseConstructor]]The function object that was used to construct this promise. Checked by the resolve method of the Promise constructor.
[[PromiseResult]]The value with which the promise has been fulfilled or rejected, if any. Only meaningful if [[PromiseState]] is not "pending".
[[PromiseFulfillReactions]]A List of PromiseReaction records to be processed when/if the promise transitions from the "pending" state to the"fulfilled" state.
[[PromiseRejectReactions]]A List of PromiseReaction records to be processed when/if the promise transitions from the "pending" state to the"rejected" state.
-
-
-
-
- -
-
-

26 Reflection

-
- -
-
-

26.1 The - Reflect Object

- -

The Reflect object is a single ordinary object.

- -

The value of the [[Prototype]] internal slot of the Reflect - object is the standard built-in Object prototype object (19.1.3).

- -

The Reflect object is not a function object. It does not have a [[Construct]] internal method; it is not possible to use - the Reflect object as a constructor with the new operator. The Reflect object also does not have a [[Call]] - internal method; it is not possible to invoke the Reflect object as a function.

-
- -
-

26.1.1 - Reflect.apply ( target, thisArgument, argumentsList )

- -

When the apply function is called with arguments target, - thisArgument, and argumentsList the following steps are taken:

- -
    -
  1. If IsCallable(target) is false, then throw a TypeError - exception.
    2. -
  2. Let args be CreateListFromArrayLike(argumentsList).
    3. -
  3. ReturnIfAbrupt(args).
    4. -
  4. Perform the PrepareForTailCall abstract operation.
    5. -
  5. Return the result of calling the [[Call]] internal method of target with arguments thisArgument and - args.
    6. -
-
- -
-

26.1.2 - Reflect.construct ( target, argumentsList )

- -

When the construct function is called with arguments target and argumentsList the - following steps are taken:

- -
    -
  1. If IsConstructor(target) is false, then throw a TypeError - exception.
    2. -
  2. Let args be CreateListFromArrayLike(argumentsList).
    3. -
  3. ReturnIfAbrupt(args).
    4. -
  4. Return the result of calling the [[Construct]] internal method of target with argument args.
    5. -
-
- -
-

26.1.3 Reflect.defineProperty ( target, propertyKey, attributes )

- -

When the defineProperty function is called with arguments target, propertyKey, and attributes the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. Let desc be the result of calling ToPropertyDescriptor with - attributes as the argument.
    6. -
  6. ReturnIfAbrupt(desc).
    7. -
  7. Return the result of calling the [[DefineOwnProperty]] internal method of obj with arguments key, and - desc.
    8. -
-
- -
-

26.1.4 Reflect.deleteProperty ( target, propertyKey )

- -

When the deleteProperty function is called with arguments target and propertyKey, the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. Return the result of calling the [[Delete]] internal method of obj with argument key.
    6. -
-
- -
-

26.1.5 - Reflect.enumerate ( target )

- -

When the enumerate function is called with argument target the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let iterator be the result of calling the [[Enumerate]] internal method of obj.
    4. -
  4. Return iterator.
    5. -
-
- -
-

26.1.6 - Reflect.get ( target, propertyKey [ , receiver ])

- -

When the get function is called with arguments target, - propertyKey, and receiver the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. If receiver is not present, then -
      -
    1. Let receiver be target.
      2. -
    -
    6. -
  6. Return the result of calling the [[Get]] internal method of obj with arguments key, and - receiver.
    7. -
-
- -
-

26.1.7 Reflect.getOwnPropertyDescriptor ( target, propertyKey )

- -

When the getOwnPropertyDescriptor function is called with arguments target and propertyKey, the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. Let desc be the result of calling the [[GetOwnProperty]] internal method of obj with argument - key.
    6. -
  6. ReturnIfAbrupt(desc).
    7. -
  7. Return the result of calling FromPropertyDescriptor(desc).
    8. -
-
- -
-

26.1.8 Reflect.getPrototypeOf ( target )

- -

When the getPrototypeOf function is called with argument target the following steps are - taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of calling the [[GetPrototypeOf]] internal method of obj.
    4. -
-
- -
-

26.1.9 - Reflect.has ( target, propertyKey )

- -

When the has function is called with arguments target and - propertyKey, the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. Return the result of calling the [[HasProperty]] internal method of obj with argument key.
    6. -
-
- -
-

26.1.10 Reflect.isExtensible (target)

- -

When the isExtensible function is called with argument target the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of calling the [[IsExtensible]] internal method of obj.
    4. -
-
- -
-

26.1.11 - Reflect.ownKeys ( target )

- -

When the ownKeys function is called with argument target the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of calling the [[OwnPropertyKeys]] internal method of obj.
    4. -
-
- -
-

26.1.12 Reflect.preventExtensions ( target )

- -

When the preventExtensions function is called with argument target, the following steps are - taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Return the result of calling the [[PreventExtensions]] internal method of obj.
    4. -
-
- -
-

26.1.13 - Reflect.set ( target, propertyKey, V [ , receiver ] )

- -

When the set function is called with arguments target, - V, propertyKey, and receiver the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. Let key be ToPropertyKey(propertyKey).
    4. -
  4. ReturnIfAbrupt(key).
    5. -
  5. If receiver is not present, then -
      -
    1. Let receiver be target.
      2. -
    -
    6. -
  6. Return the result of calling the [[Set]] internal method of obj with arguments key, V, and - receiver.
    7. -
-
- -
-

26.1.14 Reflect.setPrototypeOf ( target, proto )

- -

When the setPrototypeOf function is called with arguments target and propertyKey, the following steps are taken:

- -
    -
  1. Let obj be ToObject(target).
    2. -
  2. ReturnIfAbrupt(obj).
    3. -
  3. If Type(proto) is not Object and proto is not - null, then throw a TypeError exception
    4. -
  4. Return the result of calling the [[SetPrototypeOf]] internal method of obj with argument proto.
    5. -
-
-
- -
-
-

26.2 Realm - Objects

-
- -
-
-

26.2.1 The Reflect.Realm Constructor

- -

The initial value of Reflect.Realm is the %Realm% intrinsic object. - Reflect.Realm is the constructor for Realm - objects. When Reflect.Realm is called as a function rather than as a - constructor, it initializes its this value with the internal state necessary to support the - Reflect.Realm.prototype built-in methods.

- -

The Reflect.Realm constructor is designed to be subclassable. It may be - used as the value in an extends clause of a class definition. Subclass constructors that intend to inherit - the specified Realm behaviour must include a super call to Reflect.Realm.

-
- -
-

26.2.1.1 - Reflect.Realm ( [ target , handler ] )

- -

When the Reflect.Realm function is called with optional arguments - target and handler the following steps are taken:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or realmObject - does not have a [[RealmRecord]] internal slot, throw a - TypeError exception.
    3. -
  3. If the value of realmObject’s [[RealmRecord]] internal slot is not undefined, throw a - TypeError exception.
    4. -
  4. If any arguments were passed to this function, then -
      -
    1. Let newGlobal be ProxyCreate(target, handler).
      2. -
    2. ReturnIfAbrupt(newGlobal)
      3. -
    -
    5. -
  5. Else, -
      -
    1. Let newGlobal be undefined.
      2. -
    -
    6. -
  6. Let realmRec be CreateRealm().
    7. -
  7. Perform SetRealmGlobalObj(realmRec, newGlobal).
    8. -
  8. Let translate be GetMethod(realmObject, "directEval").
    9. -
  9. ReturnIfAbrupt(translate).
    10. -
  10. Let fallback be GetMethod(realmObject, "nonEval").
    11. -
  11. ReturnIfAbrupt(fallback).
    12. -
  12. Let indirectEval be GetMethod(realmObject, - "indirectEval").
    13. -
  13. ReturnIfAbrupt(indirectEval).
    14. -
  14. Set realmRec.[[directEvalTranslate]] to translate.
    15. -
  15. Set realmRec.[[nonEvalFallback]] to fallback.
    16. -
  16. Set realmRec.[[indirectEval]] to indirectEval.
    17. -
  17. NOTE the following step ensures that this function was not reentrantly applied to realmObject during the - above steps.
    18. -
  18. If the value of realmObject’s [[RealmRecord]] internal slot is not undefined, throw a - TypeError exception.
    19. -
  19. Set realmObject’s [[RealmRecord]] internal - slot to realmRec.
    20. -
  20. Let initGlobal be GetMethod(realmObject, "initGlobal").
    21. -
  21. ReturnIfAbrupt(initGlobal).
    22. -
  22. If initGlobal is not undefined, then -
      -
    1. Let status be the result of calling the [[Call]] internal method of initGlobal, passing - realmObject as the this value and no arguments.
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    23. -
  23. Else, -
      -
    1. Let status be SetDefaultGlobalBindings(realmRec).
      2. -
    2. ReturnIfAbrupt(status).
      3. -
    -
    24. -
  24. Return realmObject.
    25. -
-
- -
-

26.2.1.2 new Reflect.Realm ( ...argumentsList )

- -

When Reflect.Realm is called as part of a new expression it is - a constructor: it initializes a newly created object. It performs the following steps:

- -
    -
  1. Let F be the %Realm% function object on which the new operator was applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If Reflect.Realm is implemented as an ECMAScript function object, its [[Construct]] internal method will perform the - above steps.

-
-
- -
-
-

26.2.2 Properties of the Reflect.Realm Constructor

- -

The value of the [[Prototype]] internal slot of the - Reflect.Realm constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 0), the Reflect.Realm constructor has the following properties:

-
- -
-

26.2.2.1 Reflect.Realm.prototype

- -

The initial value of Reflect.Realm.prototype is the intrinsic %RealmPrototype% object (26.2.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

26.2.2.2 Reflect.Realm [ @@create ] ( )

- -

The @@create method of a Reflect.Realm function object F - performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%RealmPrototype%", ( [[RealmRecord]])).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

26.2.3 Properties of the Reflect.Realm Prototype Object

- -

The value of the [[Prototype]] internal slot of the - Reflect.Realm prototype object is the standard built-in Object prototype - object (19.1.3). The Reflect.Realm prototype object is an ordinary object. It does not have a [[RealmRecord]] internal slot.

-
- -
-

26.2.3.1 Reflect.Realm.prototype.constructor

- -

The initial value of Reflect.Realm.prototype.constructor is the built-in %Realm% constructor.

-
- -
-

26.2.3.2 Reflect.Realm.prototype.eval ( source )

- -

When Reflect.Realm.prototype.eval is called with argument source it performs the following - steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or realmObject - does not have a [[RealmRecord]] internal slot, throw a - TypeError exception.
    3. -
  3. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realm is undefined, then throw a TypeError exception.
    5. -
  5. Return the result of IndirectEval(realm, source).
    6. -
-
- -
-

26.2.3.3 get Reflect.Realm.prototype.global

- -

Reflect.Realm.prototype.global is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or realmObject - does not have a [[RealmRecord]] internal slot, throw a - TypeError exception.
    3. -
  3. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realm is undefined, then throw a TypeError exception.
    5. -
  5. Return realm.[[globalThis]].
    6. -
-
- -
-

26.2.3.4 get Reflect.Realm.prototype.intrinsics

- -

Reflect.Realm.prototype.intrinsics is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or realmObject - does not have a [[RealmRecord]] internal slot, throw a - TypeError exception.
    3. -
  3. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realm is undefined, then throw a TypeError exception.
    5. -
  5. Let table be ObjectCreate(%ObjectPrototype%).
    6. -
  6. Let intrinsics be realm’s [[instrinsics]] internal slot.
    7. -
  7. For each name in the “Intrinsic Key” column of Table 7, in row order do -
      -
    1. Let object be the value of the field of intrinsics whose name is name.
      2. -
    2. Perform CreateDataProperty(table, key, object).
      3. -
    -
    8. -
  8. Return table.
    9. -
-
- -
-

26.2.3.5 get Reflect.Realm.prototype.stdlib

- -

Reflect.Realm.prototype.stdlib is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or realmObject - does not have a [[RealmRecord]] internal slot, throw a - TypeError exception.
    3. -
  3. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realm is undefined, then throw a TypeError exception.
    5. -
  5. Let props be ObjectCreate(%ObjectPrototype%).
    6. -
  6. For each property of the Global Object specified in clause 18, do -
      -
    1. Let name be the string value of the property name.
      2. -
    2. Let desc be the fully populated data property descriptor for the property containing the specified - attributes for the property. For properties whose values are functions, the value of the [[Value]] attribute is - the corresponding intrinsic function object for realm.
      3. -
    3. Let status be DefinePropertyOrThrow(props, name, - desc).
      4. -
    4. ReturnIfAbrupt(status).
      5. -
    -
    7. -
  7. Return props.
    8. -
- -
-

NOTE The object returned is suitable for use as the second argument to Object.defineProperties. A Realm’s global - object can be initialized with its clause 18 standard values using an expression such - as:

- - 
Object.defineProperties(newRealm.global, newRealm.stdlib);
-
-
- -
-

26.2.3.6 Reflect.Realm.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Reflect.Realm".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-
-

26.2.3.7 Realm Subclass Extension Properties

- -

The following properties are intended to be over-ridden by subclasses of Reflect.Realm.

-
- -
-

26.2.3.7.1 Reflect.Realm.prototype.directEval ( source )

- -

When Reflect.Realm.prototype.directEval is called with argument source it performs the - following steps:

- -
    -
  1. Return source.
    2. -
- -
-

NOTE If an apparent direct eval call had multiple arguments, those arguments are all passed - to this function.

-
-
- -
-

26.2.3.7.2 Reflect.Realm.prototype.indirectEval ( source )

- -

When Reflect.Realm.prototype.indirectEval is called with argument source it performs the - following steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or - realmObject does not have a [[RealmRecord]] internal slot, throw a TypeError exception.
    3. -
  3. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realm is undefined, then throw a TypeError exception.
    5. -
  5. Return IndirectEval(realm, source).
    6. -
-
- -
-

26.2.3.7.3 Reflect.Realm.prototype.initGlobal ( )

- -

When Reflect.Realm.prototype.initGlobal is called it performs the following steps:

- -
    -
  1. Let realmObject be the this value.
    2. -
  2. If Type(realmObject) is not Object or - realmObject does not have a [[RealmRecord]] internal slot, throw a TypeError exception.
    3. -
  3. Let realmRec be the value of realmObject’s [[RealmRecord]] internal slot.
    4. -
  4. If realmRec is undefined, then throw a TypeError exception.
    5. -
  5. Return SetDefaultGlobalBindings(realmRec).
    6. -
-
- -
-

26.2.3.7.4 Reflect.Realm.prototype.nonEval (function, thisValue, - argumentsList )

- -

When Reflect.Realm.prototype.nonEval is called with arguments function, thisValue, - and argumentsList it performs the following steps:

- -
    -
  1. If IsCallable(function) is false, then throw a TypeError - exception.
    2. -
  2. Let args be CreateListFromArrayLike(argumentsList).
    3. -
  3. ReturnIfAbrupt(args).
    4. -
  4. Perform PrepareForTailCall( ).
    5. -
  5. Return the result of calling the [[Call]] internal method of functionwith arguments thisValue and - args.
    6. -
-
-
-
- -
-

26.2.4 Properties of Reflect.Realm Instances

- -

Reflect.Realm instances are ordinary objects that inherit properties from the - Reflect.Realm prototype object. Reflect.Realm instances each have a [[RealmRecord]] internal slot.

-
-
- -
-
-

26.3 Loader - Objects

- -

Loader objects are able to load the source code of an ECMAScript Module in the context of a - specific Realm.

-
- -
-
-

26.3.1 The Reflect.Loader Constructor

- -

The initialize value of Reflect.Loader is the %Loader% intrinsic object. Reflect.Loader is - the constructor for Loader objects. When Reflect.Loader is called as a function rather than as a constructor, - it initializes its this value with the internal state necessary to support the - Reflect.Loader.prototype built-in methods.

- -

The Reflect.Loader constructor is designed to be subclassable. It may be used as the value in an - extends clause of a class definition. Subclass constructors that intend to support the specified Loader - behaviour must include a super call to Reflect.Loader.

-
- -
-

26.3.1.1 - Reflect.Loader ( [ options ] )

- -

When the Reflect.Loader function is called with optional argument options the following steps are taken:

- -
    -
  1. Let loader be the this value.
    2. -
  2. If Type(loader) is not Object, throw a TypeError - exception.
    3. -
  3. If loader does not have a [[LoaderRecord]] internal - slot, throw a TypeError exception.
    4. -
  4. If the value of loader’s [[LoaderRecord]] internal slot is not undefined, throw a - TypeError exception.
    5. -
  5. Let realmObject be the result of GetOption(options, - "realm").
    6. -
  6. ReturnIfAbrupt(realmObject).
    7. -
  7. If realmObject is undefined, let realm be the Realm of the running execution context.
    8. -
  8. Else, -
      -
    1. If Type(realmObject) is not Object or - realmObject does not have a [[RealmRecord]] internal slot, throw a TypeError - exception.
      2. -
    2. Let realm be the value of realmObject’s [[RealmRecord]] internal slot.
      3. -
    3. If realm is undefined, throw a TypeError exception.
      4. -
    -
    9. -
  9. For each name in the List ("normalize", - "locate", "fetch", "translate", "instantiate"), -
      -
    1. Let hook be the result of GetOption(options, name).
      2. -
    2. ReturnIfAbrupt(hook).
      3. -
    3. If hook is not undefined, -
        -
      1. If IsCallable(hook) is false, throw a TypeError - exception.
        2. -
      2. Let result be CreateDataPropertyOrThrow(loader, - name, hook).
        3. -
      3. ReturnIfAbrupt(result).
        4. -
      -
      4. -
    -
    10. -
  10. NOTE the following step ensures that this function was not reentrantly applied to loader during the above steps.
    11. -
  11. If the value of loader’s [[LoaderRecord]] internal slot is not undefined, throw a - TypeError exception.
    12. -
  12. Let loaderRecord be CreateLoaderRecord(realm, - loader).
    13. -
  13. Set loader’s [[LoaderRecord]] internal - slot to loaderRecord.
    14. -
  14. Return loader.
    15. -
-
- -
-

26.3.1.2 new Reflect.Loader ( ...argumentsList )

- -

When Reflect.Loader is called as part of a new expression it is a constructor: it initializes - a newly created object. It performs the following steps:

- -
    -
  1. Let F be the Reflect.Loader function object on which the new operator was - applied.
    2. -
  2. Let argumentsList be the argumentsList argument of the [[Construct]] internal method that was invoked - by the new operator.
    3. -
  3. Return the result of Construct(F, argumentsList).
    4. -
- -

If Reflect.Loader is implemented as an ECMAScript function - object, its [[Construct]] internal method will perform the above steps.

-
-
- -
-
-

26.3.2 Properties of the Loader Constructor

- -

The value of the [[Prototype]] internal slot of the - Reflect.Loader constructor is the Function prototype object (19.2.3).

- -

Besides the length property (whose value is 0), the Reflect.Loader constructor has the - following properties:

-
- -
-

26.3.2.1 Reflect.Loader.prototype

- -

The initial value of Reflect.Loader.prototype is the intrinsic %LoaderPrototype% object (26.3.3).

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - false }.

-
- -
-

26.3.2.2 Reflect.Loader [ @@create ] ( )

- -

The @@create method of a Reflect.Loader function object F performs the following steps:

- -
    -
  1. Let F be the this value.
    2. -
  2. Let obj be the result of calling OrdinaryCreateFromConstructor(F, - "%LoaderPrototype%", ([[LoaderRecord]])).
    3. -
  3. Return obj.
    4. -
- -

The value of the name property of this function is "[Symbol.create]".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: - true }.

-
-
- -
-
-

26.3.3 Properties of the Reflect.Loader Prototype Object

- -

The value of the [[Prototype]] internal slot of the - Reflect.Loader prototype object is the standard built-in Object prototype object (19.1.3). The Reflect.Loader prototype object is an - ordinary object. It does not have a [[LoaderRecord]] internal - slot.

- -

The phrase "this Loader" within the specification of the following - methods refers to the result returned by performing the abstract operation thisLoader with the this value of the - current method invocation passed as the argument.

- -

The abstract operation thisLoader with argument value performs the following steps:

- -
    -
  1. If Type(value) is Object and value has a - [[LoaderRecord]] internal slot, then -
      -
    1. Let r be value’s [[LoaderRecord]] internal slot.
      2. -
    2. If r is not undefined, then return value.
      3. -
    -
    2. -
  2. Throw a TypeError exception.
    3. -
-
- -
-

26.3.3.1 Reflect.Loader.prototype.constructor

- -

The initial value of Reflect.Loader.prototype.constructor is the built-in %Loader% constructor.

-
- -
-

26.3.3.2 Reflect.Loader.prototype.define ( name, source [ , options ] )

- -

The define method installs a module in this loader's module registry for source - using name as the registry key. The module is not immediately available. The translate and - instantiate hooks are called asynchronously, and dependencies are loaded asynchronously. define - returns a Promise object that resolves to undefined when the new module and its dependencies - are installed in the registry.

- -

When the define method is called with arguments name, source, and optional argument - options the following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let name be ToString(name).
    5. -
  5. ReturnIfAbrupt(name).
    6. -
  6. Let address be GetOption(options, "address").
    7. -
  7. ReturnIfAbrupt(address).
    8. -
  8. Let metadata be GetOption(options, "metadata").
    9. -
  9. ReturnIfAbrupt(metadata).
    10. -
  10. If metadata is undefined then let metadata be ObjectCreate(%ObjectPrototype%).
    11. -
  11. Let p be PromiseOfStartLoadPartwayThrough("translate", - loaderRecord, name, metadata, source, address).
    12. -
  12. ReturnIfAbrupt(p).
    13. -
  13. Let G be a new function as defined by ReturnUndefined.
    14. -
  14. Let p be the result of calling PromiseThen(p, G).
    15. -
  15. Return p.
    16. -
- -

The length property of the define method is 2.

-
- -
-

26.3.3.3 Reflect.Loader.prototype.delete ( name )

- -

The delete method removes an entry whose key is name from this loader's module - registry. It performs the following steps:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let name be ToString(name).
    5. -
  5. ReturnIfAbrupt(name).
    6. -
  6. Let modules be the value of loaderRecord.[[Modules]],
    7. -
  7. Repeat for each Record {[[name]], [[value]]} p that is an element of modules, -
      -
    1. If SameValue(p.[[key]], name), then -
        -
      1. Set p.[[key]] to empty.
        2. -
      2. Set p.[[value]] to empty.
        3. -
      3. Return true.
        4. -
      -
      2. -
    -
    8. -
  8. Return false.
    9. -
-
- -
-

26.3.3.4 Reflect.Loader.prototype.entries ( )

- -

The following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Return the result of CreateLoaderIterator(loader, - "key+value").
    4. -
-
- -
-

26.3.3.5 Reflect.Loader.prototype.get ( name )

- -

If this Loader's module registry contains a Module with the given normalized name, return it. Otherwise, - return undefined. If the module is in the registry but has never been evaluated, first - synchronously evaluate the bodies of the module and any dependencies that have not evaluated yet.

- -

When the get method is called with the argument name, the following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let name be ToString(name).
    5. -
  5. ReturnIfAbrupt(name).
    6. -
  6. Let modules be the value of loaderRecord.[[Modules]],
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of modules, -
      -
    1. If SameValue(p.[[key]], name) is true, then -
        -
      1. Let module be p.[[value]].
        2. -
      2. Let result be EnsureEvaluated(module, - (),loaderRecord).
        3. -
      3. ReturnIfAbrupt(result).
        4. -
      4. Return p.[[value]].
        5. -
      -
      2. -
    -
    8. -
  8. Return undefined.
    9. -
-
- -
-

26.3.3.6 get Reflect.Loader.prototype.global

- -

Reflect.Loader.prototype.global is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let realm be the value of loaderRecord.[[Realm]].
    5. -
  5. Return realm.[[globalThis]].
    6. -
-
- -
-

26.3.3.7 Reflect.Loader.prototype.has ( name )

- -

When the Reflect.Loader.prototype.has method is called with argument name the following - steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let name be ToString(name).
    5. -
  5. ReturnIfAbrupt(name).
    6. -
  6. Let modules be the value of loaderRecord.[[Modules]],
    7. -
  7. Repeat for each Record {[[key]], [[value]]} p that is an element of modules, -
      -
    1. If SameValue(p.[[key]], name) is true, then return - true.
      2. -
    -
    8. -
  8. Return false.
    9. -
- -
-

NOTE This method does not call any hooks or run any module code.

-
-
- -
-

26.3.3.8 Reflect.Loader.prototype.import ( name [ , options ] )

- -

The import method asynchronously loads, links, and evaluates a module and all its dependencies if these - actions have not already been performed. The argument name is the registry key for the module. - import returns a Promise that resolves to the Module object once it has been committed to the - registry and evaluated.

- -

When the import method is called with argument name and optional arguments options - the following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let p be the result of calling LoadModule(loaderRecord, name, - options).
    5. -
  5. ReturnIfAbrupt(p).
    6. -
  6. Let F be a new function object as defined by EvaluateLoadedModule.
    7. -
  7. Set F’s [[Loader]] internal slot to - loaderRecord.
    8. -
  8. Let p be PromiseThen(p, F).
    9. -
  9. Return p.
    10. -
- -

If the optional argument options is an object with an address property the string value of that - property is used as the module location and module loading starts with the fetch step. If an address property - is not present, module loading starts with the locate step.

- -

The length property of the import method is 1.

- -
-

NOTE Invoking the import method is the dynamic equivalent (when combined with - normalization) of:
ImportDeclaration :: import ModuleSpecifier ;

-
-
- -
-

26.3.3.9 Reflect.Loader.prototype.keys ( )

- -

The following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Return the result of CreateLoaderIterator(loader, - "key").
    4. -
-
- -
-

26.3.3.10 Reflect.Loader.prototype.load ( name [ , options ] )

- -

The load method asynchronously loads and links and all its dependencies if these actions have not already - been performed. The argument name is the registry key for the module. load returns a Promise that - resolves to the Module object once it has been committed to the registry.

- -

When the load method is called with argument name and optional arguments options the - following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let p be the result of calling LoadModule(loaderRecord, name, - options).
    5. -
  5. ReturnIfAbrupt(p).
    6. -
  6. Let p be PromiseThen(p, %ReturnUndefined%).
    7. -
  7. Return p.
    8. -
- -

If the optional argument options is an object with an address property. The string value of - that property is used as the module location and module loading starts with the fetch step. If an address - property is not present, module loading starts with the locate step.

- -

The length property of the load method is 1.

- -
-

NOTE The load method differs from the import method in that it does - not force evaluation of the loaded module.

-
-
- -
-

26.3.3.11 Reflect.Loader.prototype.module ( source [, options ] )

- -

The module method asynchronously loads, links, and evaluates an anonymous module from source. - The module's dependencies, if any, are loaded and committed to the registry. The anonymous module itself is not added to - the registry. module returns a Promise object that resolves to a new Module instance object once the given - module body has been evaluated.

- -

When the module method is called with argument source and optional arguments options - the following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. If options was not passed, then let options be undefined.
    5. -
  5. Let address be GetOption(options, "address").
    6. -
  6. ReturnIfAbrupt(address).
    7. -
  7. Let load be CreateLoad(undefined).
    8. -
  8. Set load.[[Address]] to address.
    9. -
  9. Let linkSet be CreateLinkSet(loaderRecord, load).
    10. -
  10. Let successCallback be a new function object as defined by EvaluateLoadedModule.
    11. -
  11. Set successCallback’s [[Loader]] internal - slot to loaderRecord.
    12. -
  12. Set successCallback’s [[Load]] internal - slot to load.
    13. -
  13. Let p be the result of calling PromiseThen(linkSet.[[Done]], - successCallback).
    14. -
  14. Let sourcePromise be PromiseOf(source).
    15. -
  15. Perform ProceedToTranslate(loaderRecord, load, - sourcePromise).
    16. -
  16. Return p.
    17. -
- -

The optional argument options is an object with an address property.

- -

The length property of the module method is 1.

-
- -
-

26.3.3.12 Reflect.Loader.prototype.newModule ( obj )

- -

TO DO

- -

In the prototype this is the Module Factory Function. However, this factory seems to - have only specialized utility and it seems to unnecessarily clutter the “global” namespace of Module - abstractions. Making it a method of module loaders seems like a more sanity thing to do, but we can break it out if - that;s what people really want.

- -

Also need to reconcile with are execute factory returns by the instantiate hook. Is - this method intended to be able as an execute factory. If sho it probably needs to accept multiple arguments.

- -

When the newModule method is called with argument obj it creates a new Module objects whose - export properties are derived form the properties of obj. The following steps are performed:

- -
    -
  1. If Type(obj) is not Object, throw a TypeError - exception.
    2. -
  2. Let mod be CreateLinkedModuleInstance( )
    3. -
  3. Let keys be the result of calling the ObjectKeys abstract operation passing obj as the argument.
    4. -
  4. ReturnIfAbrupt(keys).
    5. -
  5. For each key in keys, do -
      -
    1. Let value be the result of Get(obj, key).
      2. -
    2. ReturnIfAbrupt(value).
      3. -
    3. Let F be the result of calling CreateConstantGetter(key, value).
      4. -
    4. Let desc be the PropertyDescriptor {[[Configurable]]: false, [[Enumerable]]: true, [[Get]]: - F, [[Set]]: undefined}.
      5. -
    5. Let status be the result of calling the DefinePropertyOrThrow - abstract operation passing mod, key, and desc as arguments.
      6. -
    6. ReturnIfAbrupt(status).
      7. -
    -
    6. -
  6. Call the [[PreventExtensions]] internal method of mod.
    7. -
  7. Return mod.
    8. -
-
- -
-

26.3.3.13 get Reflect.Loader.prototype.realm

- -

Reflect.Loader.prototype.realm is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Return RealmObjectFor(loaderRecord.[[Realm]]).
    5. -
-
- -
-

26.3.3.14 Reflect.Loader.prototype.set ( name, module )

- -

Store a Module obj in this Loader's module registry, - overwriting any existing entry with the same name.

- -

The following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Let loaderRecord be loader’s [[LoaderRecord]] internal slot.
    4. -
  4. Let name be ToString(name).
    5. -
  5. ReturnIfAbrupt(name).
    6. -
  6. If Type(module) is not Object, throw a TypeError - exception.
    7. -
  7. Let modules be the value of loaderRecord.[[Modules]],
    8. -
  8. Repeat for each Record {[[key]], [[value]]} p that is an element of modules, -
      -
    1. If SameValue(p.[[key]], name) is true, then -
        -
      1. Set p.[[value]] to module.
        2. -
      2. Return loader.
        3. -
      -
      2. -
    -
    9. -
  9. Let p be the Record {[[key]]: name, [[value]]: module}.
    10. -
  10. Append p as the last record of loaderRecord.[[Modules]].
    11. -
  11. Return loader.
    12. -
-
- -
-

26.3.3.15 Reflect.Loader.prototype.values ( )

- -

The following steps are taken:

- -
    -
  1. Let loader be this Loader.
    2. -
  2. ReturnIfAbrupt(loader).
    3. -
  3. Return the result of CreateLoaderIterator(loader, - "value").
    4. -
-
- -
-

26.3.3.16 Reflect.Loader.prototype[@@iterator] ( )

- -

The initial value of the @@iterator property is the same function object as the initial value of the - entries property.

-
- -
-

26.3.3.17 Reflect.Loader.prototype [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Reflect.Loader".

- -

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.

-
- -
-
-

26.3.3.18 Reflect.Loader Pipeline Hook Properties

- -

Loader hooks are methods that are called at various points in the process of loading a module. - Loader.prototype provides default implementations for the hook methods. However, individual Loader object - may over-ride these defaults using own properties.

-
- -
-

26.3.3.18.1 Reflect.Loader.prototype.normalize ( name, refererName, - refererAddress )

- -

When the normalize loader hook is called with arguments name, refererName, and - refererAddress loadRequest, the following steps are taken:

- -
    -
  1. Assert: Type(name) is String.
    2. -
  2. Return name.
    3. -
- -

This is a Loader hook that may be over-ridden by an own property of Loader instances. The normalize hook - is called once per distinct ModuleSpecifier String value in a ModuleBody, while the module ModuleBody with that is being loaded. The - name argument is the StringValue of a ModuleSpecifier.

- -

The normalize hook returns an eventual String, the normalized module name, which is used for the rest of - the import process. In particular, the [[Loads]] and [[Modules]] Lists of a ModuleLinkage record are both keyed by - normalized module names. The module registry contains at most one module for a given normalized module name.

- -

After calling this hook, if the normalized module name is in the registry or the load table, no new Load - Record is created. Otherwise the loader initiates a load for that module that starts by calling the locate - hook.

-
- -
-

26.3.3.18.2 Reflect.Loader.prototype.locate ( loadRequest )

- -

When the locate method is called with argument loadRequest the following steps are taken:

- -
    -
  1. Return the result of Get(loadRequest, "name").
    2. -
- -

This is a Loader hook that may be over-ridden by an own property of Loader instances. The locate hook is - called for each distinct normalized import ModuleSpecifier immediately after the - normalize hook returns successfully, unless the module is already loaded or loading.

- -

The locate hook is called to obtain to determine the Loader-dependent resource address (URL, path, etc.) - corresponding to normalized module name. The resource address is used later in the Loader pipeline to retrieve the - source code of the requested module.

- -

When a locate hook is called by an Loader object the argument loadRequest is a LoadRequest - object (15.2.3.2). The value of the name property - is the normalized module name. The locate hook returns an eventual value that is used as the resource - address. When the returned value is resolved, loading will continue with the fetch hook.

- -
-

NOTE The System.locate hook typically is significantly more complicated than - the default locate hook.

-
-
- -
-

26.3.3.18.3 Reflect.Loader.prototype.fetch ( loadRequest )

- -

When the fetch loader hook is called with argument loadRequest, the following steps are - taken:

- -
    -
  1. Throw a TypeError exception.
    2. -
- -

This is a Loader hook that will normally be over-ridden by an own property of Loader instances. The - fetch hook is called by a Loader for all modules whose source code was not directly provided to the Loader. - It is also used to process the import keyword. The fetch hook is not called for module bodies - directly provided as arguments to loader.module() or loader.define(). However, the - fetch hook may be called when loading other modules imported by such modules.

- -

When a fetch hook is called by an Loader object the argument loadRequest is a LoadRequest - object (15.2.3.2) with an address property. The - value of the address property identifies the module source code to fetch. The fetch hook returns an - eventual String containing the source code of the module.

-
- -
-

26.3.3.18.4 Reflect.Loader.prototype.translate ( loadRequest )

- -

When the translate method is called, the following steps are taken:

- -
    -
  1. Return the result of Get(loadRequest, "source").
    2. -
- -

This is a Loader hook that may be over-ridden by an own property of Loader instances. The - translate hook is called for each ModuleBody including those passed to - loader.module() or loader.define().The translate hook is called prior to parsing - the ModuleBody and provides a Loader the opportunity to modify or replace the source code that - will be parsed.

- -
-

NOTE An example of the use of the translate hook would be to translate source - code for a another programing language into an ECMAScript ModuleBody.

-
- -

When a translate hook is called by an Loader object the argument loadRequest is a LoadRequest - object (15.2.3.2) with address and - source properties. The value of the address property identifies the module source code to - fetch. The value of the source property is the resolved value returned from the fetch hook. - The translate hook returns either an eventual String value ECMAScript that will be parsed as a ModuleBody.

-
- -
-

26.3.3.18.5 Reflect.Loader.prototype.instantiate ( loadRequest )

- -

When the instantiate loader hook is called with argument loadRequest, the following steps are taken:

- -
    -
  1. Return undefined.
    2. -
- -

This hook allows a Loader to provide interoperability with other module systems.

- -

When a instantiate hook is called by an Loader object the argument, loadRequest, is a - LoadRequest object (15.2.3.2) with address and - source properties. loadRequest.name, loadRequest.metadata, - and loadRequest.address are the same values passed to the fetch and - translate hooks. loadRequest.source is the value produced by the - translate hook.

- -

If the instantiate hook returns an eventual undefined, then the loader uses the default linking - behaviour. It parses loadRequest.source as a Module, looks at its imports, loads its - dependencies asynchronously, and finally links them together and adds them to the registry.

- -

Otherwise, the instantiate hook must return an eventual instantiationRequest object. An - instantiateRequest object has two required properties. The value of the deps property is an - array of strings. Each string is the name of a module upon which the module identified by loadRequest has - dependencies. The value of the execute property is a function which the loader will use to create the - module and link it with its clients and dependencies. The function should expect to receive the same number of arguments - as the size of the deps array and must return an eventual Module object. The arguments are Module objects - and have a one-to-one correspondence with elements of the deps array.

- -

The module is evaluated during the linking process. First all of the modules it depends upon are linked and evaluated - , and then passed to the execute function. Then the resulting module is linked with the downstream - dependencies.

- -
-

NOTE This feature is provided in order to permit custom loaders to support using - import to import pre-ES6 modules such as AMD modules. The design requires incremental linking when such - modules are present, but it ensures that modules implemented with standard source-level module declarations can still - be statically validated.

-
-
-
-
- -
-

26.3.4 Properties of Reflect.Loader Instances

- -

Loader instances are ordinary objects that inherit properties from the %LoaderPrototype% intrinsic object. Loader - instances each have a [[Loader]] interal slot whose value after initialization is the Loader Record that the Load instance - reflects.

-
- -
-
-

26.3.5 Loader Iterator Objects

- -

A Loader Iterator object represents a specific iteration over the module registry of some specific Loader instance - object. There is not a named constructor for Loader Iterator objects. Instead, Loader iterator objects are created by - calling certain methods of Loader instance objects.

-
- -
-

26.3.5.1 CreateLoaderIterator Abstract Operation

- -

Several methods of Loader objects return Iterator objects. The abstract operation CreateLoaderIterator with arguments - loader and kind is used to create such iterator objects. It performs the following steps:

- -
    -
  1. Assert: loader is an initialized Loader instance object.
    2. -
  2. Let iterator be ObjectCreate(%LoaderIteratorPrototype%, ([[Loader]], [[LoaderNextIndex]], [[LoaderIterationKind]])).
    3. -
  3. Set iterator’s [[Loader]] internal slot - to loader.
    4. -
  4. Set iterator’s [[LoaderNextIndex]] internal - slot to 0.
    5. -
  5. Set iterator’s [[LoaderIterationKind]] internal slot to kind.
    6. -
  6. Return iterator.
    7. -
-
- -
-
-

26.3.5.2 The %LoaderIteratorPrototype% Object

- -

All Loader Iterator Objects inherit properties from the %LoaderIteratorPrototype% intrinsic object. The - %LoaderIteratorPrototype% intrinsic object is an ordinary object and its [[Prototype]] internal slot is the %ObjectPrototype% intrinsic object. In - addition, %LoaderIteratorPrototype% has the following properties:

-
- -
-

26.3.5.2.1 %LoaderIteratorPrototype%.next ( )

-
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object, throw a TypeError - exception.
    3. -
  3. If O does not have all of the internal slots of a Loader Iterator Instance (26.3.5.3), throw a TypeError exception.
    4. -
  4. Let m be the value of the [[Loader]] internal - slot of O.
    5. -
  5. Let loaderRecord be m’s [[LoaderRecord]] internal slot.
    6. -
  6. Let index be the value of the [[LoaderNextIndex]] internal slot of O.
    7. -
  7. Let itemKind be the value of the [[LoaderIterationKind]] internal slot of O.
    8. -
  8. If m is undefined, then return CreateIterResultObject(undefined, true).
    9. -
  9. Let entries be the List that is the value of the - loaderRecord.[[Modules]].
    10. -
  10. Repeat while index is less than the total number of elements of entries. The number of elements must - be redetermined each time this method is evaluated. -
      -
    1. Let e be the Record {[[key]], [[value]]} that is the value of entries[index].
      2. -
    2. Set index to index+1;
      3. -
    3. Set the [[LoaderNextIndex]] internal slot of - O to index.
      4. -
    4. If e.[[key]] is not empty, then -
        -
      1. If itemKind is "key" then, let result be e.[[key]].
        2. -
      2. Else if itemKind is "value" then, let result be e.[[value]].
        3. -
      3. Else, -
          -
        1. Assert: itemKind is "key+value".
          2. -
        2. Let result be the result of performing ArrayCreate(2).
          3. -
        3. Assert: result is a new, well-formed Array object so - the following operations will never fail.
          4. -
        4. Call CreateDataProperty(result, "0", - e.[[key]]) .
          5. -
        5. Call CreateDataProperty(result, "1", - e.[[value]]).
          6. -
        -
        4. -
      4. Return CreateIterResultObject(result, false).
        5. -
      -
      5. -
    -
    11. -
  11. Set the [[Loader]] internal slot of O to - undefined.
    12. -
  12. Return CreateIterResultObject(undefined, true).
    13. -
- -
-

NOTE Setting the [[Loader]] internal slot to undefined when the iterator is exhausted - ensures that the same iterator cannot be restarted if new entries are subsequently added. This condition is tested in - step 8.

-
-
- -
-

26.3.5.2.2 %LoaderIteratorPrototype% [ @@iterator ] ( )

- -

The following steps are taken:

- -
    -
  1. Return the this value.
    2. -
- -

The value of the name property of this function is "[Symbol.iterator]".

-
- -
-

26.3.5.2.3 %LoaderIteratorPrototype% [ @@toStringTag ]

- -

The initial value of the @@toStringTag property is the string value "Loader Iterator".

-
-
- -
-

26.3.5.3 Properties of Loader Iterator Instances

- -

Loader Iterator instances are ordinary objects that inherit properties from the %LoaderIteratorPrototype% intrinsic - object. Loader Iterator instances are initially created with the internal slots described in Table - 51.

- -
-
Table 51 — Internal Slots of Loader Iterator Instances
- - - - - - - - - - - - - - - - - -
Internal SlotDescription
[[Loader]]The Loader object that is being iterated.
[[LoaderNextIndex]]The integer index of the next Loader registry data element to be examined by this iterator.
[[LoaderIterationKind]]A string value that identifies what is to be returned for each element of the iteration. The possible values are: "key", "value", "key+value".
-
-
-
-
- -
-

26.4 The System - Object

- -

The System object is the Loader Object instance associated with the Realm of the current - global object.

-
- -
-
-

26.5 Proxy - Objects

-
- -
-
-

26.5.1 The Proxy Constructor Function

- -

The Proxy Constructor is a Built-in Function with unique [[Construct]] behaviour. It is not intended to be - subclassed.

- -

The Proxy Constructor does not have a prototype property.

- -

The value of the length property of the Proxy Constructor is 2.

-
- -
-

26.5.1.1 Proxy ( target, handler )

- -

The Proxy function is not intended to be directly called as a function. If it is called, the following - steps are performed:

- -
    -
  1. Throw a TypeError exception.
    2. -
-
- -
-

26.5.1.2 new Proxy ( target, handler )

- -

When Proxy is called as part of a new expression it is a constructor: it creates and - initializes a new exotic proxy object. Proxy called as part of a new expression with arguments - target and handler performs the following steps:

- -
    -
  1. Return ProxyCreate(target, handler).
    2. -
- -

If Proxy is implemented as an ECMAScript function object, - it must have a [[Construct]] internal method that performs the above steps.

-
-
- -
-
-

26.5.2 Properties of the Proxy Constructor Function

-
- -
-
-

26.5.2.1 Proxy.revocable ( target, handler )

- -

The Proxy.revocable function is used to create a revocable Proxy object. When - Proxy.revocable is called with arguments target and handler the following steps are - taken:

- -
    -
  1. Let p be ProxyCreate(target, handler).
    2. -
  2. ReturnIfAbrupt(p).
    3. -
  3. Let revoker be a new built-in function object as defined in 26.5.2.1.1.
    4. -
  4. Set the [[RevokableProxy]] internal slot of - revoker to p.
    5. -
  5. Let result be ObjectCreate(%ObjectPrototype%).
    6. -
  6. CreateDataProperty(result, "proxy", p).
    7. -
  7. CreateDataProperty(result, "revoke", - revoker).
    8. -
  8. Return result.
    9. -
-
- -
-

26.5.2.1.1 Proxy Revocation Functions

- -

A Proxy revocation function is an anonymous function that has the ability to invalidate a specific Proxy object.

- -

Each Proxy revocation function has a [[RevokableProxy]] internal slot.

- -

When a Proxy revocation function, F, is called the following steps are taken:

- -
    -
  1. Let p be the value of F’s [[RevokableProxy]] internal slot.
    2. -
  2. If p is null, then return undefined.
    3. -
  3. Set the value of F’s [[RevokableProxy]] internal slot to null.
    4. -
  4. Assert: p is a Proxy object.
    5. -
  5. Set the [[ProxyTarget]] internal slot of p to - null.
    6. -
  6. Set the [[ProxyHandler]] internal slot of p - to null.
    7. -
  7. Return undefined.
    8. -
-
-
-
-
-
- -
-
-

Annex A (informative) Grammar Summary

- -

TODO: The Grammars in the Annex have not yet been updated for ES6. For now, see the - grammars in the main body of the specification.

-
- -
-
-

A.1 Lexical - Grammar

- -
-
See 10.1
-
SourceCharacter ::
-
any Unicode code point
-
- -
-
See clause 11
-
InputElementDiv ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
RightBracePunctuator
-
DivPunctuator
-
- -
-
See clause 11
-
InputElementRegExp ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
RightBracePunctuator
-
RegularExpressionLiteral
-
- -
-
See clause 11
-
InputElementTemplateTail ::
-
WhiteSpace
-
LineTerminator
-
Comment
-
Token
-
DivPunctuator
-
TemplateSubstitutionTail
-
- -
-
See 11.2
-
WhiteSpace ::
-
<TAB>
-
<VT>
-
<FF>
-
<SP>
-
<NBSP>
-
<BOM>
-
<USP>
-
- -
-
See 11.3
-
LineTerminator ::
-
<LF>
-
<CR>
-
<LS>
-
<PS>
-
- -
-
See 11.3
-
LineTerminatorSequence ::
-
<LF>
-
<CR> [lookahead ∉ <LF> ]
-
<LS>
-
<PS>
-
<CR> <LF>
-
- -
-
See 11.4
-
Comment ::
-
MultiLineComment
-
SingleLineComment
-
- -
-
See 11.4
-
MultiLineComment ::
-
/* MultiLineCommentCharsopt */
-
- -
-
See 11.4
-
MultiLineCommentChars ::
-
MultiLineNotAsteriskChar MultiLineCommentCharsopt
-
* PostAsteriskCommentCharsopt
-
- -
-
See 11.4
-
PostAsteriskCommentChars ::
-
MultiLineNotForwardSlashOrAsteriskChar MultiLineCommentCharsopt
-
* PostAsteriskCommentCharsopt
-
- -
-
See 11.4
-
MultiLineNotAsteriskChar ::
-
SourceCharacter but not *
-
- -
-
See 11.4
-
MultiLineNotForwardSlashOrAsteriskChar ::
-
SourceCharacter but not one of / or *
-
- -
-
See 11.4
-
SingleLineComment ::
-
// SingleLineCommentCharsopt
-
- -
-
See 11.4
-
SingleLineCommentChars ::
-
SingleLineCommentChar SingleLineCommentCharsopt
-
- -
-
See 11.4
-
SingleLineCommentChar ::
-
SourceCharacter but not LineTerminator
-
- -
-
See 11.5
-
Token ::
-
IdentifierName
-
Punctuator
-
NumericLiteral
-
StringLiteral
-
Template
-
- -
-
See 11.6
-
IdentifierName ::
-
IdentifierStart
-
IdentifierName IdentifierPart
-
- -
-
See 11.6
-
IdentifierStart ::
-
UnicodeIDStart
-
$
-
_
-
\ UnicodeEscapeSequence
-
- -
-
See 11.6
-
IdentifierPart ::
-
UnicodeIDContinue
-
$
-
_
-
\ UnicodeEscapeSequence
-
<ZWNJ>
-
<ZWJ>
-
- -
-
See 11.6
-
UnicodeIDStart ::
-
any Unicode code point with the Unicode property “ID_Start”
-
- -
-
See 11.6
-
UnicodeIDContinue ::
-
any Unicode code point with the Unicode property “ID_Continue”
-
- -
-
See 11.6.2
-
ReservedWord ::
-
Keyword
-
FutureReservedWord
-
NullLiteral
-
BooleanLiteral
-
- -
-
See 11.6.2.1
-
Keyword :: one of
-
- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
breakdointypeof
caseelseinstanceofvar
catchexportnewvoid
classextendsreturnwhile
constfinallysuperwith
continueforswitchyield
debuggerfunctionthis
deleteimporttry
-
- -
-
See 11.6.2.2
-
FutureReservedWord ::
-
enum
-
- -

The following tokens are also considered to be FutureReservedWords when parsing strict mode code (see 10.2.1).

- -
- - - - - - - - - - - - - -
implementspackageprotectedstatic
interfaceprivatepublic
-
- -
-
See 11.7
-
Punctuator :: one of
-
- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
{}()[]
.;,<><=
>===!====!==
+-*%++--
<<>>>>>&|^
!~&&||?:
=+=-=*=%=<<=
>>=>>>=&=|=^==>
-
- -
-
See 11.7
-
DivPunctuator :: one of
-
- -
- - - - - - - - - -
//=
-
- -
-
See 11.7
-
RightBracePunctuator :: one of
-
- -
- - - - - - - - - -
}
-
- -
-
See 7.8.1
-
NullLiteral ::
-
null
-
- -
-
See 11.8.2
-
BooleanLiteral ::
-
true
-
false
-
- -
-
See 11.8.3
-
NumericLiteral ::
-
DecimalLiteral
-
BinaryIntegerLiteral
-
OctalIntegerLiteral
-
HexIntegerLiteral
-
- -
-
See 11.8.3
-
DecimalLiteral ::
-
DecimalIntegerLiteral . DecimalDigitsopt ExponentPartopt
-
. DecimalDigits ExponentPartopt
-
DecimalIntegerLiteral ExponentPartopt
-
- -
-
See 11.8.3
-
DecimalIntegerLiteral ::
-
0
-
NonZeroDigit DecimalDigitsopt
-
- -
-
See 11.8.3
-
DecimalDigits ::
-
DecimalDigit
-
DecimalDigits DecimalDigit
-
- -
-
See 11.8.3
-
DecimalDigit :: one of
-
0 1 2 3 4 5 6 7 8 9
-
- -
-
See 11.8.3
-
NonZeroDigit :: one of
-
1 2 3 4 5 6 7 8 9
-
- -
-
See 11.8.3
-
ExponentPart ::
-
ExponentIndicator SignedInteger
-
- -
-
See 11.8.3
-
ExponentIndicator :: one of
-
e E
-
- -
-
See 11.8.3
-
SignedInteger ::
-
DecimalDigits
-
+ DecimalDigits
-
- DecimalDigits
-
- -
-
See 11.8.3
-
BinaryIntegerLiteral ::
-
0b BinaryDigits
-
0B BinaryDigits
-
- -
-
See 11.8.3
-
BinaryDigits ::
-
BinaryDigit
-
BinaryDigits BinaryDigit
-
- -
-
See 11.8.3
-
BinaryDigit :: one of
-
0 1
-
- -
-
See 11.8.3
-
OctalIntegerLiteral ::
-
0o OctalDigits
-
0O OctalDigits
-
- -
-
See 11.8.3
-
OctalDigits ::
-
OctalDigit
-
OctalDigits OctalDigit
-
- -
-
See 11.8.3
-
OctalDigit :: one of
-
0 1 2 3 4 5 6 7
-
- -
-
See 11.8.3
-
HexIntegerLiteral ::
-
0x HexDigits
-
0X HexDigist
-
- -
-
See 11.8.3
-
HexDigits ::
-
HexDigit
-
HexDigits HexDigit
-
- -
-
See 11.8.3
-
HexDigit :: one of
-
0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
-
- -
-
See 11.8.4
-
StringLiteral ::
-
" DoubleStringCharactersopt "
-
' SingleStringCharactersopt '
-
- -
-
See 11.8.4
-
DoubleStringCharacters ::
-
DoubleStringCharacter DoubleStringCharactersopt
-
- -
-
See 11.8.4
-
SingleStringCharacters ::
-
SingleStringCharacter SingleStringCharactersopt
-
- -
-
See 11.8.4
-
DoubleStringCharacter ::
-
SourceCharacter but not one of " or \ or LineTerminator
-
\ EscapeSequence
-
LineContinuation
-
- -
-
See 11.8.4
-
SingleStringCharacter ::
-
SourceCharacter but not one of ' or \ or LineTerminator
-
\ EscapeSequence
-
LineContinuation
-
- -
-
See 11.8.4
-
LineContinuation ::
-
\ LineTerminatorSequence
-
- -
-
See 11.8.4
-
EscapeSequence ::
-
CharacterEscapeSequence
-
0 [lookahead ∉ DecimalDigit]
-
HexEscapeSequence
-
UnicodeEscapeSequence
-
- -
-
See 11.8.4
-
CharacterEscapeSequence ::
-
SingleEscapeCharacter
-
NonEscapeCharacter
-
- -
-
See 11.8.4
-
SingleEscapeCharacter :: one of
-
' " \ b f n r t v
-
- -
-
See 11.8.4
-
NonEscapeCharacter ::
-
SourceCharacter but not one of EscapeCharacter or LineTerminator
-
- -
-
See 11.8.4
-
EscapeCharacter ::
-
SingleEscapeCharacter
-
DecimalDigit
-
x
-
u
-
- -
-
See 11.8.4
-
HexEscapeSequence ::
-
x HexDigit HexDigit
-
- -
-
See 11.8.4
-
UnicodeEscapeSequence ::
-
u Hex4Digits
-
u{ HexDigits }
-
- -
-
See 11.8.4
-
Hex4Digits ::
-
HexDigit HexDigit HexDigit HexDigit
-
- -
-
See 11.8.5
-
RegularExpressionLiteral ::
-
/ RegularExpressionBody / RegularExpressionFlags
-
- -
-
See 11.8.5
-
RegularExpressionBody ::
-
RegularExpressionFirstChar RegularExpressionChars
-
- -
-
See 11.8.5
-
RegularExpressionChars ::
-
[empty]
-
RegularExpressionChars RegularExpressionChar
-
- -
-
See 11.8.5
-
RegularExpressionFirstChar ::
-
RegularExpressionNonTerminator but not one of * or \ or / or [
-
RegularExpressionBackslashSequence
-
RegularExpressionClass
-
- -
-
See 11.8.5
-
RegularExpressionChar ::
-
RegularExpressionNonTerminator but not one of \ or / or [
-
RegularExpressionBackslashSequence
-
RegularExpressionClass
-
- -
-
See 11.8.5
-
RegularExpressionBackslashSequence ::
-
\ RegularExpressionNonTerminator
-
- -
-
See 11.8.5
-
RegularExpressionNonTerminator ::
-
SourceCharacter but not LineTerminator
-
- -
-
See 11.8.5
-
RegularExpressionClass ::
-
[ RegularExpressionClassChars ]
-
- -
-
See 11.8.5
-
RegularExpressionClassChars ::
-
[empty]
-
RegularExpressionClassChars RegularExpressionClassChar
-
- -
-
See 11.8.5
-
RegularExpressionClassChar ::
-
RegularExpressionNonTerminator but not one of ] or \
-
RegularExpressionBackslashSequence
-
- -
-
See 11.8.5
-
RegularExpressionFlags ::
-
[empty]
-
RegularExpressionFlags IdentifierPart
-
- -
-
See 11.8.6
-
Template ::
-
NoSubstitutionTemplate
-
TemplateHead
-
- -
-
See 11.8.6
-
NoSubstitutionTemplate ::
-
` TemplateCharactersopt `
-
- -
-
See 11.8.6
-
TemplateHead ::
-
` TemplateCharactersopt ${
-
- -
-
See 11.8.6
-
TemplateSubstitutionTail ::
-
TemplateMiddle
-
TemplateTail
-
- -
-
See 11.8.6
-
TemplateMiddle ::
-
} TemplateCharactersopt ${
-
- -
-
See 11.8.6
-
TemplateTail ::
-
} TemplateCharactersopt `
-
- -
-
See 11.8.6
-
TemplateCharacters ::
-
TemplateCharacter TemplateCharactersopt
-
- -
-
See 11.8.6
-
TemplateCharacter ::
-
SourceCharacter but not one of ` or \ or $ or LineTerminatorSequence
-
$ [lookahead ≠ { ]
-
\ EscapeSequence
-
LineContinuation
-
LineTerminatorSequence
-
-
- -
-

Expressions

- -
-
See 11.1
-
PrimaryExpression :
-
this
-
Identifier
-
Literal
-
ArrayLiteral
-
ObjectLiteral
-
( Expression )
-
- -
-
See 11.1.4
-
ArrayLiteral :
-
[ Elisionopt ]
-
[ ElementList ]
-
[ ElementList , Elisionopt ]
-
- -
-
See 11.1.4
-
ElementList :
-
Elisionopt AssignmentExpression
-
ElementList , Elisionopt AssignmentExpression
-
- -
-
See 11.1.4
-
Elision :
-
,
-
Elision ,
-
- -
-
See 11.1.5
-
ObjectLiteral :
-
{ }
-
{ PropertyDefinitionList }
-
{ PropertyDefinitionList , }
-
- -
-
See 11.1.5
-
PropertyDefinitionList :
-
PropertyDefinition
-
PropertyDefinitionList , PropertyDefinition
-
- -
-
See 11.1.5
-
PropertyDefinition :
-
PropertyName : AssignmentExpression
-
get PropertyName ( ) { FunctionBody }
-
set PropertyName ( PropertySetParameterList ) { FunctionBody }
-
- -
-
See 11.1.5
-
PropertyName :
-
IdentifierName
-
StringLiteral
-
NumericLiteral
-
- -
-
See 11.1.5
-
PropertySetParameterList :
-
Identifier
-
- -
-
See 11.2
-
MemberExpression :
-
PrimaryExpression
-
FunctionExpression
-
MemberExpression [ Expression ]
-
MemberExpression . IdentifierName
-
new MemberExpression Arguments
-
- -
-
See 11.2
-
NewExpression :
-
MemberExpression
-
new NewExpression
-
- -
-
See 11.2
-
CallExpression :
-
MemberExpression Arguments
-
CallExpression Arguments
-
CallExpression [ Expression ]
-
CallExpression . IdentifierName
-
- -
-
See 11.2
-
Arguments :
-
( )
-
( ArgumentList )
-
- -
-
See 11.2
-
ArgumentList :
-
AssignmentExpression
-
ArgumentList , AssignmentExpression
-
- -
-
See 11.2
-
LeftHandSideExpression :
-
NewExpression
-
CallExpression
-
- -
-
See 11.3
-
PostfixExpression :
-
LeftHandSideExpression
-
LeftHandSideExpression [no LineTerminator here] ++
-
LeftHandSideExpression [no LineTerminator here] --
-
- -
-
See 11.4
-
UnaryExpression :
-
PostfixExpression
-
delete UnaryExpression
-
void UnaryExpression
-
typeof UnaryExpression
-
++ UnaryExpression
-
-- UnaryExpression
-
+ UnaryExpression
-
- UnaryExpression
-
~ UnaryExpression
-
! UnaryExpression
-
- -
-
See 11.5
-
MultiplicativeExpression :
-
UnaryExpression
-
MultiplicativeExpression * UnaryExpression
-
MultiplicativeExpression / UnaryExpression
-
MultiplicativeExpression % UnaryExpression
-
- -
-
See 11.6
-
AdditiveExpression :
-
MultiplicativeExpression
-
AdditiveExpression + MultiplicativeExpression
-
AdditiveExpression - MultiplicativeExpression
-
- -
-
See 11.7
-
ShiftExpression :
-
AdditiveExpression
-
ShiftExpression << AdditiveExpression
-
ShiftExpression >> AdditiveExpression
-
ShiftExpression >>> AdditiveExpression
-
- -
-
See 11.8
-
RelationalExpression :
-
ShiftExpression
-
RelationalExpression < ShiftExpression
-
RelationalExpression > ShiftExpression
-
RelationalExpression <= ShiftExpression
-
RelationalExpression >= ShiftExpression
-
RelationalExpression instanceof ShiftExpression
-
RelationalExpression in ShiftExpression
-
- -
-
See 11.9
-
EqualityExpression :
-
RelationalExpression
-
EqualityExpression == RelationalExpression
-
EqualityExpression != RelationalExpression
-
EqualityExpression === RelationalExpression
-
EqualityExpression !== RelationalExpression
-
- -
-
See 11.10
-
BitwiseANDExpression :
-
EqualityExpression
-
BitwiseANDExpression & EqualityExpression
-
- -
-
See 11.10
-
BitwiseXORExpression :
-
BitwiseANDExpression
-
BitwiseXORExpression ^ BitwiseANDExpression
-
- -
-
See 11.10
-
BitwiseORExpression :
-
BitwiseXORExpression
-
BitwiseORExpression | BitwiseXORExpression
-
- -
-
See 11.11
-
LogicalANDExpression :
-
BitwiseORExpression
-
LogicalANDExpression && BitwiseORExpression
-
- -
-
See 11.11
-
LogicalORExpression :
-
LogicalANDExpression
-
LogicalORExpression || LogicalANDExpression
-
- -
-
See 11.12
-
ConditionalExpression :
-
LogicalORExpression
-
LogicalORExpression ? AssignmentExpression : AssignmentExpression
-
- -
-
See 11.13
-
AssignmentExpression :
-
ConditionalExpression
-
LeftHandSideExpression = AssignmentExpression
-
LeftHandSideExpression AssignmentOperator AssignmentExpression
-
- -
-
See 11.13
-
AssignmentOperator : one of
-
- -
- - - - - - - - - - - - - - -
*=/=%=+=-=<<=>>=>>>=&=^=|=
-
- -
-
See 11.14
-
Expression :
-
AssignmentExpression
-
Expression , AssignmentExpression
-
-
- -
-

Statements

- -
-
See clause 12
-
Statement :
-
Block
-
VariableStatement
-
EmptyStatement
-
ExpressionStatement
-
IfStatement
-
IterationStatement
-
ContinueStatement
-
BreakStatement
-
ReturnStatement
-
WithStatement
-
LabelledStatement
-
SwitchStatement
-
ThrowStatement
-
TryStatement
-
DebuggerStatement
-
- -
-
See 12.1
-
Block :
-
{ StatementListopt }
-
- -
-
See 12.1
-
StatementList :
-
Statement
-
StatementList Statement
-
- -
-
See 12.2
-
VariableStatement :
-
var VariableDeclarationList ;
-
- -
-
See 12.2
-
VariableDeclarationList :
-
VariableDeclaration
-
VariableDeclarationList , VariableDeclaration
-
- -
-
See 12.2
-
VariableDeclaration :
-
Identifier Initialiseropt
-
- -
-
See 12.2
-
Initialiser :
-
= AssignmentExpression
-
- -
-
See 12.3
-
EmptyStatement :
-
;
-
- -
-
See 12.4
-
ExpressionStatement :
-
[lookahead ∉ {{, function}] Expression ;
-
- -
-
See 12.5
-
IfStatement :
-
if ( Expression ) Statement else Statement
-
if ( Expression ) Statement
-
- -
-
See 12.6
-
IterationStatement :
-
do Statement while ( Expression ) ;
-
while ( Expression ) Statement
-
for ( Expressionopt ; Expressionopt ; Expressionopt ) Statement
-
for ( var VariableDeclarationList ; Expressionopt ; Expressionopt ) Statement
-
for ( LeftHandSideExpression in Expression ) Statement
-
for ( var VariableDeclaration in Expression ) Statement
-
- -
-
See 12.7
-
ContinueStatement :
-
continue ;
-
continue [no LineTerminator here] Identifier ;
-
- -
-
See 12.8
-
BreakStatement :
-
break ;
-
break [no LineTerminator here] Identifier ;
-
- -
-
See 12.9
-
ReturnStatement :
-
return ;
-
return [no LineTerminator here] Expression ;
-
- -
-
See 12.10
-
WithStatement :
-
with ( Expression ) Statement
-
- -
-
See 12.11
-
SwitchStatement :
-
switch ( Expression ) CaseBlock
-
- -
-
See 12.11
-
CaseBlock :
-
{ CaseClausesopt }
-
{ CaseClausesopt DefaultClause CaseClausesopt }
-
- -
-
See 12.11
-
CaseClauses :
-
CaseClause
-
CaseClauses CaseClause
-
- -
-
See 12.11
-
CaseClause :
-
case Expression : StatementListopt
-
- -
-
See 12.11
-
DefaultClause :
-
default : StatementListopt
-
- -
-
See 12.12
-
LabelledStatement :
-
Identifier : Statement
-
- -
-
See 12.13
-
ThrowStatement :
-
throw [no LineTerminator here] Expression ;
-
- -
-
See 12.14
-
TryStatement :
-
try Block Catch
-
try Block Finally
-
try Block Catch Finally
-
- -
-
See 12.14
-
Catch :
-
catch ( Identifier ) Block
-
- -
-
See 12.14
-
Finally :
-
finally Block
-
- -
-
See 12.15
-
DebuggerStatement :
-
debugger ;
-
-
- -
-

Functions and Scripts

- -
-
See clause 13
-
FunctionDeclaration :
-
function Identifier ( FormalParameterListopt ) { FunctionBody }
-
- -
-
See clause 13
-
FunctionExpression :
-
function Identifieropt ( FormalParameterListopt ) { FunctionBody }
-
- -
-
See clause 13
-
FormalParameterList :
-
Identifier
-
FormalParameterList , Identifier
-
- -
-
See clause 13
-
FunctionBody :
-
SourceElementsopt
-
- -
-
See clause 14
-
Program :
-
SourceElementsopt
-
- -
-
See clause 14
-
SourceElements :
-
SourceElement
-
SourceElements SourceElement
-
- -
-
See clause 14
-
SourceElement :
-
Statement
-
FunctionDeclaration
-
-
- -
-

Number Conversions

- -
-
See 7.1.3.1
-
StringNumericLiteral :::
-
StrWhiteSpaceopt
-
StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt
-
- -
-
See 7.1.3.1
-
StrWhiteSpace :::
-
StrWhiteSpaceChar StrWhiteSpaceopt
-
- -
-
See 7.1.3.1
-
StrWhiteSpaceChar :::
-
WhiteSpace
-
LineTerminator
-
- -
-
See 7.1.3.1
-
StrNumericLiteral :::
-
StrDecimalLiteral
-
HexIntegerLiteral
-
- -
-
See 7.1.3.1
-
StrDecimalLiteral :::
-
StrUnsignedDecimalLiteral
-
+ StrUnsignedDecimalLiteral
-
- StrUnsignedDecimalLiteral
-
- -
-
See 7.1.3.1
-
StrUnsignedDecimalLiteral :::
-
Infinity
-
DecimalDigits . DecimalDigitsopt ExponentPartopt
-
. DecimalDigits ExponentPartopt
-
DecimalDigits ExponentPartopt
-
- -
-
See 7.1.3.1
-
DecimalDigits :::
-
DecimalDigit
-
DecimalDigits DecimalDigit
-
- -
-
See 7.1.3.1
-
DecimalDigit ::: one of
-
0 1 2 3 4 5 6 7 8 9
-
- -
-
See 7.1.3.1
-
ExponentPart :::
-
ExponentIndicator SignedInteger
-
- -
-
See 7.1.3.1
-
ExponentIndicator ::: one of
-
e E
-
- -
-
See 7.1.3.1
-
SignedInteger :::
-
DecimalDigits
-
+ DecimalDigits
-
- DecimalDigits
-
- -
-
See 7.1.3.1
-
HexIntegerLiteral :::
-
0x HexDigit
-
0X HexDigit
-
HexIntegerLiteral HexDigit
-
- -
-
See 7.1.3.1
-
HexDigit ::: one of
-
0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
-
-
- -
-

Universal Resource Identifier Character Classes

- -
-
See 15.1.3
-
uri :::
-
uriCharactersopt
-
- -
-
See 15.1.3
-
uriCharacters :::
-
uriCharacter uriCharactersopt
-
- -
-
See 15.1.3
-
uriCharacter :::
-
uriReserved
-
uriUnescaped
-
uriEscaped
-
- -
-
See 15.1.3
-
uriReserved ::: one of
-
; / ? : @ & = + $ ,
-
- -
-
See 15.1.3
-
uriUnescaped :::
-
uriAlpha
-
DecimalDigit
-
uriMark
-
- -
-
See 15.1.3
-
uriEscaped :::
-
% HexDigit HexDigit
-
- -
-
See 15.1.3
-
uriAlpha ::: one of
-
a b c d e f g h i j k l m n o p q r s t u v w x y z
-
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
-
- -
-
See 15.1.3
-
uriMark ::: one of
-
- _ . ! ~ * ' ( )
-
-
- -
-

Regular Expressions

- -
-
See 15.10.1
-
Pattern ::
-
Disjunction
-
- -
-
See 15.10.1
-
Disjunction ::
-
Alternative
-
Alternative | Disjunction
-
- -
-
See 15.10.1
-
Alternative ::
-
[empty]
-
Alternative Term
-
- -
-
See 15.10.1
-
Term ::
-
Assertion
-
Atom
-
Atom Quantifier
-
- -
-
See 15.10.1
-
Assertion ::
-
^
-
$
-
\ b
-
\ B
-
( ? = Disjunction )
-
( ? ! Disjunction )
-
- -
-
See 15.10.1
-
Quantifier ::
-
QuantifierPrefix
-
QuantifierPrefix ?
-
- -
-
See 15.10.1
-
QuantifierPrefix ::
-
*
-
+
-
?
-
{ DecimalDigits }
-
{ DecimalDigits , }
-
{ DecimalDigits , DecimalDigits }
-
- -
-
See 15.10.1
-
Atom ::
-
PatternCharacter
-
.
-
\ AtomEscape
-
CharacterClass
-
( Disjunction )
-
( ? : Disjunction )
-
- -
-
See 15.10.1
-
PatternCharacter ::
-
SourceCharacter but not one of -
-
^ $ \ . * + ? ( ) [ ] { } |
-
- -
-
See 15.10.1
-
AtomEscape ::
-
DecimalEscape
-
CharacterEscape
-
CharacterClassEscape
-
- -
-
See 15.10.1
-
CharacterEscape ::
-
ControlEscape
-
c ControlLetter
-
HexEscapeSequence
-
UnicodeEscapeSequence
-
IdentityEscape
-
- -
-
See 15.10.1
-
ControlEscape :: one of
-
f n r t v
-
- -
-
See 15.10.1
-
ControlLetter :: one of
-
a b c d e f g h i j k l m n o p q r s t u v w x y z
-
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
-
- -
-
See 15.10.1
-
IdentityEscape ::
-
SourceCharacter but not IdentifierPart
-
<ZWJ>
-
<ZWNJ>
-
- -
-
See 15.10.1
-
DecimalEscape ::
-
DecimalIntegerLiteral [lookahead ∉ DecimalDigit]
-
- -
-
See 15.10.1
-
CharacterClassEscape :: one of
-
d D s S w W
-
- -
-
See 15.10.1
-
CharacterClass ::
-
[ [lookahead ∉ {^}] ClassRanges ]
-
[ ^ ClassRanges ]
-
- -
-
See 15.10.1
-
ClassRanges ::
-
[empty]
-
NonemptyClassRanges
-
- -
-
See 15.10.1
-
NonemptyClassRanges ::
-
ClassAtom
-
ClassAtom NonemptyClassRangesNoDash
-
ClassAtom – ClassAtom ClassRanges
-
- -
-
See 15.10.1
-
NonemptyClassRangesNoDash ::
-
ClassAtom
-
ClassAtomNoDash NonemptyClassRangesNoDash
-
ClassAtomNoDash – ClassAtom ClassRanges
-
- -
-
See 15.10.1
-
ClassAtom ::
-
-
-
ClassAtomNoDash
-
- -
-
See 15.10.1
-
ClassAtomNoDash ::
-
SourceCharacter but not one of \ or ] or -
-
\ ClassEscape
-
- -
-
See 15.10.1
-
ClassEscape ::
-
DecimalEscape
-
b
-
CharacterEscape
-
CharacterClassEscape
-
-
-
-
- -
-
-

Annex B (normative) Additional ECMAScript - Features for Web Browsers

- -

The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript host is a web browser. - The content of this annex is normative but optional if the ECMAScript host is not a web browser.

-
- -
-
-

B.1 - Additional Syntax

-
- -
-

B.1.1 Numeric Literals

- -

The syntax and semantics of 11.8.3 is extended as follows except that this - extension is not allowed for strict mode code:

- -

Syntax

- -
-
NumericLiteral ::
-
DecimalLiteral
-
BinaryIntegerLiteral
-
OctalIntegerLiteral
-
HexIntegerLiteral
-
LegacyOctalIntegerLiteral
-
- -
-
LegacyOctalIntegerLiteral ::
-
0 OctalDigit
-
LegacyOctalIntegerLiteral OctalDigit
-
- -

B.1.1.1 Static Semantics

- -
    -
  • -

    The MV of LegacyOctalIntegerLiteral :: 0 OctalDigit is the MV of OctalDigit.

    -
    • - -
  • -

    The MV of LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit is (the MV of LegacyOctalIntegerLiteral times 8) plus the MV of OctalDigit.

    -
    • -
-
- -
-

B.1.2 String Literals

- -

The syntax and semantics of 11.8.4 is extended as follows except that this - extension is not allowed for strict mode code:

- -

Syntax

- -
-
EscapeSequence ::
-
CharacterEscapeSequence
-
OctalEscapeSequence
-
HexEscapeSequence
-
UnicodeEscapeSequence
-
- -
-
OctalEscapeSequence ::
-
OctalDigit [lookahead ∉ DecimalDigit]
-
ZeroToThree OctalDigit [lookahead ∉ DecimalDigit]
-
FourToSeven OctalDigit
-
ZeroToThree OctalDigit OctalDigit
-
- -
-
ZeroToThree :: one of
-
0 1 2 3
-
- -
-
FourToSeven :: one of
-
4 5 6 7
-
- -

This definition of EscapeSequence is not used when parsing TemplateCharacter (11.8.6).

- -

B.1.2.1 Static Semantics

- -
    -
  • The CV of EscapeSequence :: OctalEscapeSequence is the CV of the OctalEscapeSequence.
    • -
  • The CV of OctalEscapeSequence :: OctalDigit is the character whose code unit value is the MV of the OctalDigit.
    • -
  • The CV of OctalEscapeSequence :: ZeroToThree OctalDigit is the character whose code unit value is (8 - times the MV of the ZeroToThree) plus the MV of the OctalDigit.
    • -
  • The CV of OctalEscapeSequence :: FourToSeven OctalDigit is the character whose code unit value is (8 - times the MV of the FourToSeven) plus the MV of the OctalDigit.
    • -
  • The CV of OctalEscapeSequence :: ZeroToThree OctalDigit OctalDigit is the - character whose code unit value is (64 (that is, 82) times the MV of the ZeroToThree) plus (8 times - the MV of the first OctalDigit) plus the MV of the second OctalDigit.
    • -
  • The MV of ZeroToThree :: 0 is 0.
    • -
  • The MV of ZeroToThree :: 1 is 1.
    • -
  • The MV of ZeroToThree :: 2 is 2.
    • -
  • The MV of ZeroToThree :: 3 is 3.
    • -
  • The MV of FourToSeven :: 4 is 4.
    • -
  • The MV of FourToSeven :: 5 is 5.
    • -
  • The MV of FourToSeven :: 6 is 6.
    • -
  • The MV of FourToSeven :: 7 is 7.
    • -
-
- -
-

B.1.3 - HTML-like Comments

- -

TODO See http://javascript.spec.whatwg.org/#comment-syntax

-
- -
-

B.1.4 Regular Expressions Patterns

- -

The syntax of 21.2.1 is extended as modified and extended as follows. These changes introduce - ambiguities that are broken by the ordering or grammar productions and by contextual information. The following grammar is - used, with each alternative considered only if previous production alternatives do not match.

- -

Syntax

- -
-
Term[U] ::
-
[~U] ExtendedTerm
-
[+U] Assertion[U]
-
[+U] Atom[U]
-
[+U] Atom[U] Quantifier
-
- -
-
ExtendedTerm ::
-
Assertion
-
AtomNoBrace Quantifier
-
Atom
-
QuantifiableAssertion Quantifier
-
- -
-
AtomNoBrace ::
-
PatternCharacterNoBrace
-
.
-
\ AtomEscape
-
CharacterClass
-
( Disjunction )
-
( ? : Disjunction )
-
- -
-
Atom[U] ::
-
PatternCharacter
-
.
-
\ AtomEscape[?U]
-
CharacterClass[?U]
-
( Disjunction[?U] )
-
( ? : Disjunction[?U] )
-
- -
-
PatternCharacterNoBrace ::
-
SourceCharacter but not one of
-
^ $ \ . * + ? ( ) [ ] { } |
-
- -
-
PatternCharacter ::
-
SourceCharacter but not one of
-
^ $ \ . * + ? ( ) [ ] |
-
- -
-
QuantifiableAssertion ::
-
( ? = Disjunction )
-
( ? ! Disjunction )
-
- -
-
Assertion[U] ::
-
^
-
$
-
\ b
-
\ B
-
[+U] ( ? = Disjunction[?U] )
-
[+U] ( ? ! Disjunction[?U] )
-
[~U] QuantifiableAssertion
-
- -
-
AtomEscape[U] ::
-
[+U] DecimalEscape
-
[~U] DecimalEscape but only if the integer value of DecimalEscape is <= NCapturingParens
-
[+U] CharacterEscape[U]
-
[+U] CharacterClassEscape
-
[~U] CharacterClassEscape
-
[~U] CharacterEscape
-
- -
-
CharacterEscape[U] ::
-
ControlEscape
-
c ControlLetter
-
HexEscapeSequence
-
RegExpUnicodeEscapeSequence[?U]
-
[~U] OctalEscapeSequence
-
IdentityEscape[?U]
-
- -
-
IdentityEscape[U] ::
-
[+U] SyntaxCharacter
-
[~U] SourceCharacter but not c
-
[~U] <ZWJ>
-
[~U] <ZWNJ>
-
- -
-
NonemptyClassRanges[U] ::
-
ClassAtom[?U]
-
ClassAtom[?U] NonemptyClassRangesNoDash[?U]
-
[+U] ClassAtom[U] - ClassAtom[U] ClassRanges[U]
-
[~U] ClassAtomInRange - ClassAtomInRange ClassRanges
-
- -
-
NonemptyClassRangesNoDash[U] ::
-
ClassAtom[?U]
-
ClassAtomNoDash[?U] NonemptyClassRangesNoDash[?U]
-
[+U] ClassAtomNoDash[U] - ClassAtom[U] ClassRanges[U]
-
[~U] ClassAtomNoDashInRange - ClassAtomInRange ClassRanges
-
- -
-
ClassAtom[U] ::
-
-
-
ClassAtomNoDash[?U]
-
- -
-
ClassAtomNoDash[U] ::
-
SourceCharacter but not one of \ or ] or -
-
\ ClassEscape[?U]
-
- -
-
ClassAtomInRange ::
-
-
-
ClassAtomNoDashInRange
-
- -
-
ClassAtomNoDashInRange ::
-
SourceCharacter but not one of \ or ] or -
-
\ ClassEscape but only if ClassEscape evaluates to a CharSet with exactly one character
-
\ IdentityEscape
-
- -
-
ClassEscape[U] ::
-
[+U] DecimalEscape
-
[~U] DecimalEscape but only if the integer value of DecimalEscape is <= NCapturingParens
-
b
-
[+U] CharacterEscape[U]
-
[+U] CharacterClassEscape
-
[~U] CharacterClassEscape
-
[~U] CharacterEscape
-
- -

B.1.4.1 Pattern Semantics

- -

The semantics of 21.2.2 is extended as follows:

- -

Within 21.2.2.5 reference to “Atom :: ( Disjunction ) ” - are to be interpreted as meaning “Atom :: ( Disjunction ) or AtomNoBrace :: ( Disjunction ) ”.

- -

Term (21.2.2.5) includes the following additional evaluation rule:

- -

The production Term :: QuantifiableAssertion Quantifier evaluates the same as the production Term :: Atom Quantifier but with QuantifiableAssertion substituted for Atom.

- -

Atom (21.2.2.8) evaluation rules for the Atom productions except for - Atom :: PatternCharacter - are also used for the AtomNoBrace productions, but with AtomNoBrace - substituted for Atom. The following evaluation rule is also - added:

- -

The production AtomNoBrace :: PatternCharacterNoBrace evaluates as follows:

- -
    -
  1. Let ch be the character represented by PatternCharacterNoBrace.
    2. -
  2. Let A be a one-element CharSet containing the character ch.
    3. -
  3. Call CharacterSetMatcher(A, false) and return its Matcher result.
    4. -
- -

CharacterEscape (21.2.2.10) includes the following additional evaluation rule:

- -

The production CharacterEscape :: OctalEscapeSequence evaluates by evaluating the CV of the OctalscapeSequence (see B.1.2) and returning its - character result.

- -

ClassAtom (21.2.2.17) includes the following additional evaluation rules:

- -

The production ClassAtomInRange :: - evaluates by returning the CharSet containing the one character -.

- -

The production ClassAtomInRange :: ClassAtomNoDashInRange evaluates by evaluating ClassAtomNoDashInRange to - obtain a CharSet and returning that CharSet.

- -

ClassAtomNoDash (21.2.2.18) includes the following additional evaluation rules:

- -

The production ClassAtomNoDashInRange :: SourceCharacter but not one of \ or ] or - evaluates - by returning a one-element CharSet containing the character represented by SourceCharacter.

- -

The production ClassAtomNoDashInRange :: \ ClassEscape but ony if…, evaluates by evaluating ClassEscape to obtain a CharSet and returning that CharSet.

- -

The production ClassAtomNoDashInRange :: \ IdentityEscape evaluates by returning the character represented by IdentityEscape.

-
-
- -
-
-

B.2 Additional Built-in Properties

- -

When the ECMAScript host is a web browser the following additional properties of the standard built-in objects are - defined.

-
- -
-
-

B.2.1 Additional Properties of the Global Object

-
- -
-

B.2.1.1 - escape (string)

- -

The escape function is a property of the global object. It computes a new version of a String value in - which certain characters have been replaced by a hexadecimal escape sequence.

- -

For those characters being replaced whose code unit value is 0xFF or less, a two-digit escape sequence of - the form %xx is used. For those characters being replaced whose code unit value is greater than - 0xFF, a four-digit escape sequence of the form %uxxxx is used.

- -

When the escape function is called with one argument string, the following steps are taken:

- -
    -
  1. Let string be ToString(string).
    2. -
  2. ReturnIfAbrupt(string).
    3. -
  3. Let length be the number of code units in string.
    4. -
  4. Let R be the empty string.
    5. -
  5. Let k be 0.
    6. -
  6. Repeat, while k < length, -
      -
    1. Let char be the code unit (represented as a 16-bit unsigned integer) at position k within - string.
      2. -
    2. If char is the code point of one of the 69 nonblank - characters
      ″ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@*_+-./″
      then, -
        -
      1. Let S be a String containing the single character char.
        2. -
      -
      3. -
    3. Else if char > 256, -
        -
      1. Let S be a String containing six characters ″%uwxyz″ - where wxyz are four hexadecimal digits encoding the value of char.
        2. -
      -
      4. -
    4. Else, char < 256 -
        -
      1. Let S be a String containing three characters ″%xy″ - where xy are two hexadecimal digits encoding the value of char.
        2. -
      -
      5. -
    5. Let R be a new String value computed by concatenating the previous value of R and S.
      6. -
    6. Increase k by 1.
      7. -
    -
    7. -
  7. Return R.
    8. -
- -
-

NOTE The encoding is partly based on the encoding described in RFC 1738, but the entire - encoding specified in this standard is described above without regard to the contents of RFC 1738. This encoding does - not reflect changes to RFC 1738 made by RFC 3986.

-
-
- -
-

B.2.1.2 - unescape (string)

- -

The unescape function is a property of the global object. It computes a new version of a String value in - which each escape sequence of the sort that might be introduced by the escape function is replaced with the - character that it represents.

- -

When the unescape function is called with one argument string, the following steps are - taken:

- -
    -
  1. Let string be ToString(string).
    2. -
  2. ReturnIfAbrupt(string).
    3. -
  3. Let length be the number of code units in string.
    4. -
  4. Let R be the empty String.
    5. -
  5. Let k be 0.
    6. -
  6. Repeat, while k ≠ length -
      -
    1. Let c be the code unit at position k within string.
      2. -
    2. If c is %, -
        -
      1. If k ≤ length−6 and the code unit at position k+1 within string is - u and the four code units at positions k+2, k+3, k+4, and k+5 - within string are all hexadecimal digits, then -
          -
        1. Let c be the code unit whose value is the integer represented by the four hexadecimal digits at - positions k+2, k+3, k+4, and k+5 within string.
          2. -
        2. Increase k by 5.
          3. -
        -
        2. -
      2. Else if k ≤ length−3 and the two code units at positions k+1 and k+2 - within string are both hexadecimal digits, then -
          -
        1. Let c be the code unit whose value is the integer represented by two zeroes plus the two - hexadecimal digits at positions k+1 and k+2 within string.
          2. -
        2. Increase k by 2.
          3. -
        -
        3. -
      -
      3. -
    3. Let R be a new String value computed by concatenating the previous value of R and c.
      4. -
    4. Increase k by 1.
      5. -
    -
    7. -
  7. Return R.
    8. -
-
-
- -
-
-

B.2.2 Additional Properties of the Object.prototype Object

-
- -
-
-

B.2.2.1 Object.prototype.__proto__

- -

Object.prototype.__proto__ is an accessor property with attributes { [[Enumerable]]: false, [[Configurable]]: true }. The [[Get]] and [[Set]] attributes are - defined as follows

-
- -
-

B.2.2.1.1 get Object.prototype.__proto__

- -

The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following - steps:

- -
    -
  1. Let O be the result of calling ToObject passing the this value as the - argument.
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. Return the result of calling the [[GetPrototypeOf]] internal method of O.
    4. -
-
- -
-

B.2.2.1.2 set Object.prototype.__proto__

- -

The value of the [[Set]] attribute is a built-in function that takes an argument proto. It performs the - following steps:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. ReturnIfAbrupt(O).
    3. -
  3. If Type(proto) is neither Object nor Null, then return - undefined.
    4. -
  4. If Type(O) is not Object, then return - undefined.
    5. -
  5. Let status be the result of calling the [[SetPrototypeOf]] internal method of O with argument - proto.
    6. -
  6. ReturnIfAbrupt(status).
    7. -
  7. If status is false, then throw a TypeError exception.
    8. -
  8. Return undefined.
    9. -
-
-
-
- -
-
-

B.2.3 Additional Properties of the String.prototype Object

-
- -
-

B.2.3.1 String.prototype.substr (start, length)

- -

The substr method takes two arguments, start and length, and returns a substring of - the result of converting the this object to a String, starting from character position start and running - for length characters (or through the end of the String if length is undefined). If - start is negative, it is treated as (sourceLength+start) where sourceLength is the length of the String. The result is - a String value, not a String object. The following steps are taken:

- -
    -
  1. Let O be CheckObjectCoercible(this value).
    2. -
  2. Let S be ToString(O).
    3. -
  3. Let intStart be ToInteger(start).
    4. -
  4. ReturnIfAbrupt(intStart).
    5. -
  5. If length is undefined, let end be +∞; otherwise let end be ToInteger(length).
    6. -
  6. ReturnIfAbrupt(end).
    7. -
  7. Let size be the number of characters in S.
    8. -
  8. If intStart is negative, then let intStart be max(size + intStart,0).
    9. -
  9. Let resultLength be min(max(end,0), size – intStart).
    10. -
  10. If resultLength ≤ 0, return the empty String "".
    11. -
  11. Return a String containing resultLength consecutive characters from S beginning with the character at - position intStart.
    12. -
- -

The length property of the substr method is 2.

- -
-

NOTE The substr function is intentionally generic; it does not require that its - this value be a String object. Therefore it can be transferred to other kinds of objects for use as a method.

-
-
- -
-
-

B.2.3.2 String.prototype.anchor ( name )

- -

When the anchor method is called with argument name, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "a", "name", - name).
    3. -
-
- -
-

B.2.3.2.1 - CreateHTML ( name ) Abstract Operation

- -

The abstract operation CreateHTML is called with arguments - string, tag, attribute, and value. The - arguments tag and attribute must be string values. The following steps are taken:

- -
    -
  1. Let str be CheckObjectCoercible(string).
    2. -
  2. Let S be ToString(str).
    3. -
  3. ReturnIfAbrupt(S).
    4. -
  4. Let p1 be the string value that is the concatenation of "<" and tag.
    5. -
  5. If attribute is not the empty String, then -
      -
    1. Let V be ToString(value).
      2. -
    2. ReturnIfAbrupt(V).
      3. -
    3. Let escapedV be the string value that is the same as V except that each occurrence of the - character " (code unit value 0x0022) in V has been replaced with the six character - sequence "&quot;".
      4. -
    4. Let p1 be the string value that is the concatenation of the following string values: -
        -
      • The string value of p1
        • -
      • Code unit 0x0020 (a single SPACE)
        • -
      • The string value of attribute
        • -
      • Code unit 0x003D (a single =)
        • -
      • Code unit 0x0022 (a single QUOTATION MARK)
        • -
      • The string value of escapedV
        • -
      • Code unit 0x0022 (a single QUOTATION MARK)
        • -
      -
      5. -
    -
    6. -
  6. Let p2 be the string value that is the concatenation of p1 and ">".
    7. -
  7. Let p3 be the string value that is the concatenation of p2 and S.
    8. -
  8. Let p4 be the string value that is the concatenation of p3, "</", tag, and - ">".
    9. -
  9. Return p4.
    10. -
-
-
- -
-

B.2.3.3 String.prototype.big ()

- -

When the big method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "big", "", - "").
    3. -
-
- - - -
-

B.2.3.5 String.prototype.bold ()

- -

When the bold method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "b", "", "").
    3. -
-
- -
-

B.2.3.6 String.prototype.fixed ()

- -

When the fixed method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "tt", "", "").
    3. -
-
- -
-

B.2.3.7 String.prototype.fontcolor ( color )

- -

When the fontcolor method is called with argument color, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "font", "color", - color).
    3. -
-
- -
-

B.2.3.8 String.prototype.fontsize ( size )

- -

When the fontsize method is called with argument size, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "font", "size", - size).
    3. -
-
- -
-

B.2.3.9 String.prototype.italics ()

- -

When the italics method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "i", "", "").
    3. -
-
- - - -
-

B.2.3.11 String.prototype.small ()

- -

When the small method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "small", "", - "").
    3. -
-
- -
-

B.2.3.12 String.prototype.strike ()

- -

When the strike method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "strike", "", - "").
    3. -
-
- -
-

B.2.3.13 String.prototype.sub ()

- -

When the sub method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "sub", "", - "").
    3. -
-
- -
-

B.2.3.14 String.prototype.sup ()

- -

When the sup method is called with no arguments, the following steps are taken:

- -
    -
  1. Let S be the this value.
    2. -
  2. Return CreateHTML(S, "sup", "", - "").
    3. -
-
-
- -
-
-

B.2.4 Additional Properties of the Date.prototype Object

-
- -
-

B.2.4.1 Date.prototype.getYear ( )

- -
-

NOTE The getFullYear method is preferred for nearly all purposes, because it - avoids the “year 2000 problem.”

-
- -

When the getYear method is called with no arguments, the following steps are taken:

- -
    -
  1. Let t be this time value.
    2. -
  2. ReturnIfAbrupt(t).
    3. -
  3. If t is NaN, return NaN.
    4. -
  4. Return YearFromTime(LocalTime(t)) − - 1900.
    5. -
-
- -
-

B.2.4.2 Date.prototype.setYear (year)

- -
-

NOTE The setFullYear method is preferred for nearly all purposes, because it - avoids the “year 2000 problem.”

-
- -

When the setYear method is called with one argument year, the following steps are taken:

- -
    -
  1. Let t be LocalTime(this - time value); but if this time value is NaN, - let t be +0.
    2. -
  2. Let y be ToNumber(year).
    3. -
  3. If y is NaN, set the [[DateValue]] internal - slot of this Date object to NaN and return NaN.
    4. -
  4. If y is not NaN and 0 ≤ ToInteger(y) ≤ 99 then let - yyyy be ToInteger(y) + 1900. Otherwise, let yyyy be - y.
    5. -
  5. Let d be MakeDay(yyyy, MonthFromTime(t), DateFromTime(t)).
    6. -
  6. Let date be UTC(MakeDate(d, TimeWithinDay(t))).
    7. -
  7. Set the [[DateValue]] internal slot of this Date - object to TimeClip(date).
    8. -
  8. Return the value of the [[DateValue]] internal slot of - this Date object.
    9. -
-
- -
-

B.2.4.3 Date.prototype.toGMTString ( )

- -
-

NOTE The property toUTCString is preferred. The toGMTString - property is provided principally for compatibility with old code. It is recommended that the toUTCString - property be used in new ECMAScript code.

-
- -

The Function object that is the initial value of Date.prototype.toGMTString is the same Function object - that is the initial value of Date.prototype.toUTCString.

-
-
- -
-
-

B.2.5 Additional Properties of the RegExp.prototype Object

-
- -
-

B.2.5.1 RegExp.prototype.compile (pattern, flags )

- -

When the compile method is called with arguments pattern and flags, the following steps are - taken:

- -
    -
  1. Let O be the this value.
    2. -
  2. If Type(O) is not Object or Type(O) is Object and O does not have a - [[RegExpMatcher]] internal slot, then -
      -
    1. Throw a TypeError exception.
      2. -
    -
    3. -
  3. Let extensible be the result of calling the [[IsExtensible]] internal method of O.
    4. -
  4. ReturnIfAbrupt(extensible).
    5. -
  5. If extensible is false, then throw a TypeError exception.
    6. -
  6. If Type(pattern) is Object and pattern has a - [[RegExpMatcher]] internal slot, then -
      -
    1. If the value of pattern’s [[RegExpMatcher]] internal slot is undefined, then throw a - TypeError exception.
      2. -
    2. If flags is not undefined, then throw a TypeError exception.
      3. -
    3. Let P be the value of pattern’s [[OriginalSource]] internal slot.
      4. -
    4. Let F be the value of pattern’s [[OriginalFlags]] internal slot.
      5. -
    -
    7. -
  7. Else, -
      -
    1. Let P be pattern.
      2. -
    2. Let F be flags.
      3. -
    -
    8. -
  8. Return RegExpInitialize(O, P, F).
    9. -
- -
-

NOTE The compile method completely reinitializes the this object RegExp - with a new pattern and flags. An implementaton may interpret use of this method as an assertion that the resulting - RegExp object will be used multiple times and hence is a candidate for extra optimization.

-
-
-
-
- -
-
-

B.3 - Other Additional Features

-
- -
-

B.3.1 __proto__ Property Names in Object Initializers

- -

In 12.2.5.9 the - PropertyDefinitionEvaluation algorithm for the production PropertyDefinition - : PropertyName : AssignmentExpression is replaced with the following:

- -
PropertyDefinition : PropertyName : AssignmentExpression
-
    -
  1. Let propKey be the result of evaluating PropertyName.
    2. -
  2. ReturnIfAbrupt(propKey).
    3. -
  3. Let exprValueRef be the result of evaluating AssignmentExpression.
    4. -
  4. Let propValue be GetValue(exprValueRef).
    5. -
  5. ReturnIfAbrupt(propValue).
    6. -
  6. If propKey is the string value "__proto__" and if IsComputedPropertyKey(propKey) is - false, then -
      -
    1. If Type(propValue) is either Object or Null, then -
        -
      1. Return the result of calling the [[SetPrototypeOf]] internal method of object with argument - propValue.
        2. -
      -
      2. -
    2. Return NormalCompletion(empty).
      3. -
    -
    7. -
  7. If IsAnonymousFunctionDefinition(AssignmentExpression) is - true, then -
      -
    1. Assert: propValue is an ECMAScript function object.
      2. -
    2. Let referencesSuper be the value of propValue’s [[NeedsSuper]] internal slot.
      3. -
    3. If referencesSuper is true, then -
        -
      1. Set the propValue’s [[HomeObject]] internal slot to object.
        2. -
      2. Set the propValue’s [[MethodName]] internal slot to propKey.
        3. -
      -
      4. -
    4. SetFunctionName(propValue, propKey).
      5. -
    -
    8. -
  8. Let desc be the Property Descriptor{[[Value]]: - propValue, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true}
    9. -
  9. Return DefinePropertyOrThrow(object, propKey, - desc).
    10. -
-
- -
-

B.3.2 Web Legacy Compatibility for Block-Level Function Declarations

- -

Prior to the Sixth Edition, the ECMAScript specification did not define the occurrence of a FunctionDeclaration as an element of a Block statement’s StatementList. However, support for that form of FunctionDeclaration was an - allowable extension and most browser-hosted ECMAScript implementations permitted them. Unfortunately, the semantics of such - declarations differ among those implementations. Because of these semantic differences, existing web ECMAScript code that - uses Block level function declarations is only portable among browser implementation if the usage - only depends upon the semantic intersection of all of the browser implementations for such declarations. The following are - the use cases that fall within that intersection semantics:

- -
    -
  1. A function is declared and only referenced within a single block -
      -
    • -

      A function declaration with the name f is declared exactly once within the function code of an - enclosing function g and that declaration is nested within a Block.

      -
      • - -
    • -

      No other declaration of f that is not a var declaration occurs within the function code - of g

      -
      • - -
    • -

      All references to f occur within the StatementList of the Block containing the declaration of f.

      -
      • -
    -
    2. -
  2. A function is declared and possibly used within a single Block but also referenced by an inner - function definition that is not contained within that same Block. -
      -
    • -

      A function declaration with the name f is declared exactly once within the function code of an - enclosing function g and that declaration is nested within a Block.

      -
      • - -
    • -

      No other declaration of f that is not a var declaration occurs within the function code - of g

      -
      • - -
    • -

      References to f may occur within the StatementList of the Block containing the declaration of f.

      -
      • - -
    • -

      References to f occur within the function code of g that lexically follows the Block containing the declaration of f.

      -
      • -
    -
    3. -
  3. A function is declared and possibly used within a single block but also referenced within subsequent blocks. -
      -
    • -

      A function declaration with the name f is declared exactly once within the function code of an - enclosing function g and that declaration is nested within a Block.

      -
      • - -
    • -

      No other declaration of f that is not a var declaration occurs within the function code - of g

      -
      • - -
    • -

      References to f may occur within the StatementList of the Block containing the declaration of f.

      -
      • - -
    • -

      References to f occur within another function h that is nested within g and no - other declaration of f shadows the references to f from within h.

      -
      • - -
    • -

      All invocations of h occur after the declaration of f has been evaluated.

      -
      • -
    -
    4. -
- -

The first use case is interoperable with the semantics of Block level function declarations - provided by ECMA-262 Edition 6. Any pre-existing ECMAScript code that employees that use case will operate using the Block - level function declarations semantics defined by clauses 9, 13, and 14 of this specification.

- -

Sixth edition interoperability for the second and third use cases requires the following extensions to the clause 9 and 14 semantics. These extensions are applied to each - non-strict mode function g for each FunctionDeclaration f that is directly contained in the - StatementList of a Block, CaseClause, or DefaultClause that is part of the function code of - g

- -
    -
  1. Let F be StringValue of the BindingIdentifier of FunctionDeclaration f.
    2. -
  2. If replacing the FunctionDeclaration f with a VariableStatement that has F as a - BindingIdentifier would not produce any Early Errors for g, then -
      -
    1. During FunctionDeclarationInstantiation (9.2.13) for g perform the following steps immediately - before performing step 30: -
        -
      1. NOTE A var binding for F is only instantiated here if it is not also a VarDeclaredName, the name of a formal parameter, or - another FunctionDeclarations.
        2. -
      2. If instantiatedVarNames does not contain F, then -
          -
        1. Let status be the result of calling env’s CreateMutableBinding concrete method passing - F as the argument.
          2. -
        2. NOTE The new binding is not initialized during FunctionDeclarationInstantiation.
          3. -
        3. Assert: status is never an abrupt completion.
          4. -
        4. In place of the FunctionDeclaration Evaluation algorithm provide in 14.1.17, perform the following - steps to evaluate the FunctionDeclaration f: -
            -
          1. Let fenv be the running execution context’s VariableEnvironment.
            2. -
          2. Let benv be the running execution context’s LexicalEnvironment.
            3. -
          3. Let fobj be the result of calling the GetBindingValue concrete method of benv with - arguments F and false.
            4. -
          4. If the binding for F in fenv has not been initialized, then
            5. -
          5. Call the InitializeBinding concrete method of fenv with arguments F and - fobj.
            6. -
          6. Return NormalCompletion(empty).
            7. -
          -
          5. -
        -
        3. -
      -
      2. -
    -
    3. -
- -

If an ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a warning should be produced - for each function g whose function code contains a FunctionDeclaration for which step 2.a above will be - performed.

-
- -
-

B.3.3 VariableStatements in Catch blocks

- -

The content of subclause 13.14.1 is replaced with the - following:

- -
Catch : catch ( CatchParameter ) Block
-
    -
  • -

    It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the - LexicallyDeclaredNames of Block.

    -
    • - -
  • -

    It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the - VarDeclaredNames of Block, unless that element is only bound by a VariableStatment or the - VariableDeclarationList of a for statement, or the ForBinding of a for-in statement.

    -
    • -
- -
-

NOTE The Block of a Catch clause may contain var declarations that - bind a name that is also bound by the CatchParameter. At runtime, such bindings are instantiated in the - VariableDeclarationEnvironment. They do not shadow the same-named bindings introduced by the CatchParameter and - hence the Initializer for such var declarations will assign to the corresponding catch parameter - rather than the var binding. The relaxation of the normal static semantic rule does not apply to names only - bound by for-of statements.

-
-
-
-
- -
-

Annex C (informative) The Strict Mode of - ECMAScript

- -

The strict mode restriction and exceptions

- - -
- -
-
-

Annex D (informative) Corrections and - Clarifications That May Introduce Incompatibilities with Prior Editions

-
- -
-

D.1 In the 6th Edition

- -

9: In Edition 6, Function calls are not allowed to return a Reference - value.

- -

13.6: In Edition 6, a terminating semi-colon is no longer required at the end of a - do-while statement.

- -

13.6: Prior to Edition 6, an initialization expression could appear as part of the - VariableDeclaration that precedes the in keyword. The value of that expression was always discarded. In - Edition 6, the ForBind in that same position does not allow the occurance of such an initializer.

- -

13.14: In Edition 6, it is an early error for a Catch clause to - contained a var declaration for the same Identifier that appears as the Catch clause parameter. In previous editions, such a variable declaration would be instantiated in the - enclosing variable environment but the declaration’s Initializer value would be assigned to the - Catch parameter.

- -

14.3 In Edition 6, the function objects that are created as the values of the [[Get]] - or [[Set]] attribute of accessor properties in an ObjectLiteral are not constructor functions. In - Edition 5, they were constructors.

- -

0 and 19.1.2.3: In Edition 6, all property additions and changes are processed, - even if one of them throws an exception. If an exception occurs during such processing, the first such exception is thrown - after all propertie are processed. In Edition 5, processing of property additions and changes immediately terminated when the - first exception occurred.

- -

19.1.2.5: In Edition 6, if the argument to Object.freeze is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.6: In Edition 6, if the argument to Object.getOwnPropertyDescriptor is not an object an attempt is make to - coerce the argument using ToObject. If the coerecion is successful the result is used in place of - the original argument value. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.7: In Edition 6, if the argument to Object.getOwnPropertyNames is not an object an attempt is make to coerce the - argument using ToObject. If the coerecion is successful the result is used in place of the - original argument value. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.9: In Edition 6, if the argument to Object.getPrototypeOf is not an object an attempt is make to coerce the argument - using ToObject. If the coerecion is successful the result is used in place of the original - argument value. In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.11: In Edition 6, if the argument to Object.isExtensible is not an object it is treated as if it was a non-extensible - ordinary object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.12: In Edition 6, if the argument to Object.isFrozen is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.13: In Edition 6, if the argument to Object.isSealed is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.14: In Edition 6, if the argument to Object.keys is not an object an attempt is make to coerce the argument using ToObject. If the coerecion is successful the result is used in place of the original argument value. - In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.15: In Edition 6, if the argument to Object.preventExtensions is not an object it is treated as if it was a - non-extensible ordinary object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.17: In Edition 6, if the argument to Object.seal is not an object it is treated as if it was a non-extensible ordinary object - with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.2.4.1: In Edition 6, the length property of function instances - is configurable. In previous editions it was non-configurable.

- -

19.3.3 In Edition 6, the Boolean prototype object is not a - Boolean instance. In previous editions it was a Boolean instance whose Boolean value was false.

- -

20.1.3 In Edition 6, the Number prototype object is not a - Number instance. In previous editions it was a Number instance whose number value was +0.

- -

20.3.4 In Edition 6, the Date prototype object is not a Date - instance. In previous editions it was a Date instance whose TimeValue was NaN.

- -

22.1.3 In Edition 6, the Array prototype object is not an Array - instance. In previous editions it was an Array instance with a length property whose value was +0.

- -

21.1.3 In Edition 6, the String prototype object is not a - String instance. In previous editions it was a String instance whose String value was the empty string.

- -

21.1.3.22 and 21.1.3.24 In - Edition 6, lowercase/upper conversion processing operates on code points. In previous editions such the conversion processing - was only applied to individual code units. The only affected code points are those in the Deseret block of Unicode

- -

21.1.3.25 In Edition 6, the String.prototype.trim method is defined to recognize white space code points that - may exists outside of the Unicode BMP. However, as of Unicode 6.1 no such code points are defined. In previous editions such - code points would not have been recognized as white space.

- -

21.2.5 In Edition 6, the RegExp prototype object is not a - RegExp instance. In previous editions it was a RegExp instance whose pattern is the empty string.

- -

21.2.5 In Edition 6, source, global, - ignoreCase, and multiline are accessor properties defined on the RegExp prototype object. In - previous editions they were data properties defined on RegExp instances.

- -

22.1.3 In Edition 6, the Array prototype object is not an Array - instance. In previous editions it was an Array instance with a length property whose value was +0.

-
- -
-

D.2 In the 5th Edition

- -

Clause references in this list refer to the clause numbers used in Edition 5 and 5.1.

- -

7.1: Unicode format control characters are no longer stripped from ECMAScript source text before processing. In Edition 5, - if such a character appears in a StringLiteral or RegularExpressionLiteral the - character will be incorporated into the literal where in Edition 3 the character would not be incorporated into the - literal.

- -

7.2: Unicode character <BOM> is now treated as whitespace and its presence in the middle of what appears to be an - identifier could result in a syntax error which would not have occurred in Edition 3

- -

7.3: Line terminator characters that are preceded by an escape sequence are now allowed within a string literal token. In - Edition 3 a syntax error would have been produced.

- -

7.8.5: Regular expression literals now return a unique object each time the literal is evaluated. This change is detectable - by any programs that test the object identity of such literal values or that are sensitive to the shared side effects.

- -

7.8.5: Edition 5 requires early reporting of any possible RegExp constructor errors that would be produced when converting - a RegularExpressionLiteral to a RegExp object. Prior to Edition 5 implementations were permitted to - defer the reporting of such errors until the actual execution time creation of the object.

- -

7.8.5: In Edition 5 unescaped “/” characters may appear as a CharacterClass in a - regular expression literal. In Edition 3 such a character would have been interpreted as the final character of the - literal.

- -

10.4.2: In Edition 5, indirect calls to the eval function use the - global environment as both the variable environment and lexical environment for - the eval code. In Edition 3, the variable and lexical environments of the caller of an indirect eval was used as - the environments for the eval code.

- -

15.4.3: In Edition 5 all methods of Array.prototype are intentionally generic. In Edition 3 - toString and toLocaleString were not generic and would throw a TypeError exception if - applied to objects that were not instances of Array.

- -

10.6: In Edition 5 the array indexed properties of argument objects that correspond to actual formal parameters are - enumerable. In Edition 3, such properties were not enumerable.

- -

10.6: In Edition 5 the value of the [[Class]] internal slot - of an arguments object is "Arguments". In Edition 3, it was "Object". This is observable if - toString is called as a method of an arguments object.

- -

12.6.4: for-in statements no longer throw a TypeError if the in expression evaluates to null or - undefined. Instead, the statement behaves as if the value of the expression was an object with no enumerable - properties.

- -

15: In Edition 5, the following new properties are defined on built-in objects that exist in Edition 3: Object.getPrototypeOf, Object.getOwnPropertyDescriptor, Object.getOwnPropertyNames, Object.create, Object.defineProperty, Object.defineProperties, Object.seal, Object.freeze, Object.preventExtensions, Object.isSealed, Object.isFrozen, - Object.isExtensible, Object.keys, Function.prototype.bind, Array.prototype.indexOf, Array.prototype.lastIndexOf, Array.prototype.every, Array.prototype.some, Array.prototype.forEach, Array.prototype.map, Array.prototype.filter, Array.prototype.reduce, Array.prototype.reduceRight, String.prototype.trim, Date.now, - Date.prototype.toISOString, Date.prototype.toJSON.

- -

15: Implementations are now required to ignore extra arguments to standard built-in methods unless otherwise explicitly - specified. In Edition 3 the handling of extra arguments was unspecified and implementations were explicitly allowed to throw a - TypeError exception.

- -

15.1.1: The value properties NaN, Infinity, and undefined of the Global Object have been changed to be - read-only properties.

- -

15.1.2.1. Implementations are no longer permitted to restrict the use of eval in ways that are not a direct call. In - addition, any invocation of eval that is not a direct call uses the global - environment as its variable environment rather than the caller’s variable environment.

- -

15.1.2.2: The specification of the function parseInt no longer allows implementations to treat Strings - beginning with a 0 character as octal values.

- -

15.3.3.3: In Edition 3, a TypeError is thrown if the second argument passed to Function.prototype.apply is neither an array object nor an arguments object. - In Edition 5, the second argument may be any kind of generic array-like object that has a valid length - property.

- -

15.3.3.3, 15.3.3.4: In Edition 3 passing undefined or null as the first argument to either Function.prototype.apply or Function.prototype.call causes the global object to be passed to the indirectly - invoked target function as the this value. If the first argument is a primitive value the result of calling ToObject on the primitive value is passed as the this value. In Edition 5, these - transformations are not performed and the actual first argument value is passed as the this value. This difference will - normally be unobservable to existing ECMAScript Edition 3 code because a corresponding transformation takes place upon - activation of the target function. However, depending upon the implementation, this difference may be observable by host - object functions called using apply or call. In addition, invoking a standard built-in function in - this manner with null or undefined passed as the this value will in many cases cause behaviour in Edition - 5 implementations that differ from Edition 3 behaviour. In particular, in Edition 5 built-in functions that are specified to - actually use the passed this value as an object typically throw a TypeError exception if passed null or - undefined as the this value.

- -

15.3.4.2: In Edition 5, the prototype property of Function instances is not enumerable. In Edition 3, this - property was enumerable.

- -

15.5.5.2: In Edition 5, the individual characters of a String object’s [[StringData]] may be accessed as array - indexed properties of the String object. These properties are non-writable and non-configurable and shadow any inherited - properties with the same names. In Edition 3, these properties did not exist and ECMAScript code could dynamically add and - remove writable properties with such names and could access inherited properties with such names.

- -

15.9.4.2: Date.parse is now required to first attempt to parse its argument as - an ISO format string. Programs that use this format but depended upon implementation specific behaviour (including failure) - may behave differently.

- -

15.10.2.12: In Edition 5, \s now additionally matches <BOM>.

- -

15.10.4.1: In Edition 3, the exact form of the String value of the source property of an object created by the - RegExp constructor is implementation defined. In Edition 5, the String must conform to certain specified - requirements and hence may be different from that produced by an Edition 3 implementation.

- -

15.10.6.4: In Edition 3, the result of RegExp.prototype.toString - need not be derived from the value of the RegExp object’s source property. In Edition 5 the result must be - derived from the source property in a specified manner and hence may be different from the result produced by an - Edition 3 implementation.

- -

15.11.2.1, 15.11.4.3: In Edition 5, if an initial value for the message property of an Error object is not - specified via the Error constructor the initial value of the property is the empty String. In Edition 3, such an - initial value is implementation defined.

- -

15.11.4.4: In Edition 3, the result of Error.prototype.toString - is implementation defined. In Edition 5, the result is fully specified and hence may differ from some Edition 3 - implementations.

- -

15.12: In Edition 5, the name JSON is defined in the global - environment. In Edition 3, testing for the presence of that name will show it to be undefined unless it is defined - by the program or implementation.

-
-
- -
-
-

Annex E (informative) Additions and - Changes that Introduce Incompatibilities with Prior Editions

-
- -
-

E.1 In the 6th Edition

- -

9: In Edition 6, Function calls are not allowed to return a Reference - value.

- -

13.6: In Edition 6, a terminating semi-colon is no longer required at the end of a - do-while statement.

- -

13.6: Prior to Edition 6, an initialization expression could appear as part of the - VariableDeclaration that precedes the in keyword. The value of that expression was always discarded. In - Edition 6, the ForBind in that same position does not allow the occurrence of such an initializer.

- -

13.14: In Edition 6, it is an early error for a Catch clause to - contain a var declaration for the same Identifier that appears as the Catch clause parameter. In previous editions, such a variable declaration would be instantiated in the - enclosing variable environment but the declaration’s Initializer value would be assigned to the - Catch parameter.

- -

14.3 In Edition 6, the function objects that are created as the values of the [[Get]] - or [[Set]] attribute of accessor properties in an ObjectLiteral are not constructor functions. In - Edition 5, they were constructors.

- -

0 and 19.1.2.3: In Edition 6, all property additions and changes are processed, - even if one of them throws an exception. If an exception occurs during such processing, the first such exception is thrown - after all properties are processed. In Edition 5, processing of property additions and changes immediately terminated when the - first exception occurred.

- -

19.1.2.5: In Edition 6, if the argument to Object.freeze is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.6: In Edition 6, if the argument to Object.getOwnPropertyDescriptor is not an object an attempt is made to - coerce the argument using ToObject. If the coerecion is successful the result is used in place of - the original argument value. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.7: In Edition 6, if the argument to Object.getOwnPropertyNames is not an object an attempt is made to coerce the - argument using ToObject. If the coercion is successful the result is used in place of the - original argument value. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.9: In Edition 6, if the argument to Object.getPrototypeOf is not an object an attempt is made to coerce the argument - using ToObject. If the coercion is successful the result is used in place of the original - argument value. In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.11: In Edition 6, if the argument to Object.isExtensible is not an object it is treated as if it was a non-extensible - ordinary object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be thrown.

- -

19.1.2.12: In Edition 6, if the argument to Object.isFrozen is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

- -

19.1.2.13: In Edition 6, if the argument to Object.isSealed is not an object it is treated as if it was a non-extensible ordinary - object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

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19.1.2.14: In Edition 6, if the argument to Object.keys is not an object an attempt is make to coerce the argument using ToObject. If the coerecion is successful the result is used in place of the original argument value. - In Edition 5, a non-object argument always causes a TypeError to be thrown.

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19.1.2.15: In Edition 6, if the argument to Object.preventExtensions is not an object it is treated as if it was a - non-extensible ordinary object with no own properties. In Edition 5, a non-object argument always causes a TypeError to be thrown.

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19.1.2.17: In Edition 6, if the argument to Object.seal is not an object it is treated as if it was a non-extensible ordinary object - with no own properties. In Edition 5, a non-object argument always causes a TypeError to be - thrown.

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19.2.4.1: In Edition 6, the length property of function instances - is configurable. In previous editions it was non-configurable.

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19.3.3 In Edition 6, the Boolean prototype object is not a - Boolean instance. In previous editions it was a Boolean instance whose Boolean value was false.

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20.1.3 In Edition 6, the Number prototype object is not a - Number instance. In previous editions it was a Number instance whose number value was +0.

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20.3.4 In Edition 6, the Date prototype object is not a Date - instance. In previous editions it was a Date instance whose TimeValue was NaN.

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22.1.3 In Edition 6, the Array prototype object is not an Array - instance. In previous editions it was an Array instance with a length property whose value was +0.

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21.1.3 In Edition 6, the String prototype object is not a - String instance. In previous editions it was a String instance whose String value was the empty string.

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21.1.3.22 and 21.1.3.24 In - Edition 6, lowercase/upper conversion processing operates on code points. In previous editions such the conversion processing - was only applied to individual code units. The only affected code points are those in the Deseret block of Unicode

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21.1.3.25 In Edition 6, the String.prototype.trim method is defined to recognize white space code points that - may exists outside of the Unicode BMP. However, as of Unicode 6.1 no such code points are defined. In previous editions such - code points would not have been recognized as white space.

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21.2.5 In Edition 6, the RegExp prototype object is not a - RegExp instance. In previous editions it was a RegExp instance whose pattern is the empty string.

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21.2.5 In Edition 6, source, global, - ignoreCase, and multiline are accessor properties defined on the RegExp prototype object. In - previous editions they were data properties defined on RegExp instances.

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22.1.3 In Edition 6, the Array prototype object is not an Array - instance. In previous editions it was an Array instance with a length property whose value was +0.

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E.2 In the 5th Edition

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Clause references in this list refer to the clause numbers used in Edition 5 and 5.1.

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7.1: Unicode format control characters are no longer stripped from ECMAScript source text before processing. In Edition 5, - if such a character appears in a StringLiteral or RegularExpressionLiteral the - character will be incorporated into the literal where in Edition 3 the character would not be incorporated into the - literal.

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7.2: Unicode character <BOM> is now treated as whitespace and its presence in the middle of what appears to be an - identifier could result in a syntax error which would not have occurred in Edition 3

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7.3: Line terminator characters that are preceded by an escape sequence are now allowed within a string literal token. In - Edition 3 a syntax error would have been produced.

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7.8.5: Regular expression literals now return a unique object each time the literal is evaluated. This change is detectable - by any programs that test the object identity of such literal values or that are sensitive to the shared side effects.

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7.8.5: Edition 5 requires early reporting of any possible RegExp constructor errors that would be produced when converting - a RegularExpressionLiteral to a RegExp object. Prior to Edition 5 implementations were permitted to - defer the reporting of such errors until the actual execution time creation of the object.

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7.8.5: In Edition 5 unescaped “/” characters may appear as a CharacterClass in a - regular expression literal. In Edition 3 such a character would have been interpreted as the final character of the - literal.

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10.4.2: In Edition 5, indirect calls to the eval function use the - global environment as both the variable environment and lexical environment for - the eval code. In Edition 3, the variable and lexical environments of the caller of an indirect eval were used - as the environments for the eval code.

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15.4.3: In Edition 5 all methods of Array.prototype are intentionally generic. In Edition 3 - toString and toLocaleString were not generic and would throw a TypeError exception if - applied to objects that were not instances of Array.

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10.6: In Edition 5 the array indexed properties of argument objects that correspond to actual formal parameters are - enumerable. In Edition 3, such properties were not enumerable.

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10.6: In Edition 5 the value of the [[Class]] internal slot - of an arguments object is "Arguments". In Edition 3, it was "Object". This is observable if - toString is called as a method of an arguments object.

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12.6.4: for-in statements no longer throw a TypeError if the in expression evaluates to null or - undefined. Instead, the statement behaves as if the value of the expression was an object with no enumerable - properties.

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15: In Edition 5, the following new properties are defined on built-in objects that exist in Edition 3: Object.getPrototypeOf, Object.getOwnPropertyDescriptor, Object.getOwnPropertyNames, Object.create, Object.defineProperty, Object.defineProperties, Object.seal, Object.freeze, Object.preventExtensions, Object.isSealed, Object.isFrozen, - Object.isExtensible, Object.keys, Function.prototype.bind, Array.prototype.indexOf, Array.prototype.lastIndexOf, Array.prototype.every, Array.prototype.some, Array.prototype.forEach, Array.prototype.map, Array.prototype.filter, Array.prototype.reduce, Array.prototype.reduceRight, String.prototype.trim, Date.now, - Date.prototype.toISOString, Date.prototype.toJSON.

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15: Implementations are now required to ignore extra arguments to standard built-in methods unless otherwise explicitly - specified. In Edition 3 the handling of extra arguments was unspecified and implementations were explicitly allowed to throw a - TypeError exception.

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15.1.1: The value properties NaN, Infinity, and undefined of the Global Object have been changed to be - read-only properties.

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15.1.2.1. Implementations are no longer permitted to restrict the use of eval in ways that are not a direct call. In - addition, any invocation of eval that is not a direct call uses the global - environment as its variable environment rather than the caller’s variable environment.

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15.1.2.2: The specification of the function parseInt no longer allows implementations to treat Strings - beginning with a 0 character as octal values.

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15.3.3.3: In Edition 3, a TypeError is thrown if the second argument passed to Function.prototype.apply is neither an array object nor an arguments object. - In Edition 5, the second argument may be any kind of generic array-like object that has a valid length - property.

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15.3.3.3, 15.3.3.4: In Edition 3 passing undefined or null as the first argument to either Function.prototype.apply or Function.prototype.call causes the global object to be passed to the indirectly - invoked target function as the this value. If the first argument is a primitive value the result of calling ToObject on the primitive value is passed as the this value. In Edition 5, these - transformations are not performed and the actual first argument value is passed as the this value. This difference will - normally be unobservable to existing ECMAScript Edition 3 code because a corresponding transformation takes place upon - activation of the target function. However, depending upon the implementation, this difference may be observable by host - object functions called using apply or call. In addition, invoking a standard built-in function in - this manner with null or undefined passed as the this value will in many cases cause behaviour in Edition - 5 implementations that differ from Edition 3 behaviour. In particular, in Edition 5 built-in functions that are specified to - actually use the passed this value as an object typically throw a TypeError exception if passed null or - undefined as the this value.

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15.3.4.2: In Edition 5, the prototype property of Function instances is not enumerable. In Edition 3, this - property was enumerable.

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15.5.5.2: In Edition 5, the individual characters of a String object’s [[StringData]] may be accessed as array - indexed properties of the String object. These properties are non-writable and non-configurable and shadow any inherited - properties with the same names. In Edition 3, these properties did not exist and ECMAScript code could dynamically add and - remove writable properties with such names and could access inherited properties with such names.

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15.9.4.2: Date.parse is now required to first attempt to parse its argument as - an ISO format string. Programs that use this format but depended upon implementation specific behaviour (including failure) - may behave differently.

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15.10.2.12: In Edition 5, \s now additionally matches <BOM>.

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15.10.4.1: In Edition 3, the exact form of the String value of the source property of an object created by the - RegExp constructor is implementation defined. In Edition 5, the String must conform to certain specified - requirements and hence may be different from that produced by an Edition 3 implementation.

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15.10.6.4: In Edition 3, the result of RegExp.prototype.toString - need not be derived from the value of the RegExp object’s source property. In Edition 5 the result must be - derived from the source property in a specified manner and hence may be different from the result produced by an - Edition 3 implementation.

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15.11.2.1, 15.11.4.3: In Edition 5, if an initial value for the message property of an Error object is not - specified via the Error constructor the initial value of the property is the empty String. In Edition 3, such an - initial value is implementation defined.

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15.11.4.4: In Edition 3, the result of Error.prototype.toString - is implementation defined. In Edition 5, the result is fully specified and hence may differ from some Edition 3 - implementations.

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15.12: In Edition 5, the name JSON is defined in the global - environment. In Edition 3, testing for the presence of that name will show it to be undefined unless it is defined - by the program or implementation.

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Bibliography

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[1] ISO 8601:2004(E) Data elements and interchange formats – Information - interchange — Representation of dates and times

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[2] RFC 1738 “Uniform Resource Locators (URL)”, available at - <http://tools.ietf.org/html/rfc1738>

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[3] RFC 2396 “Uniform Resource Identifiers (URI): Generic Syntax”, available at - <http://tools.ietf.org/html/rfc2396>

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[4] RFC 3629 “UTF-8, a transformation format of ISO 10646”, available at - <http://tools.ietf.org/html/rfc3629>

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[5] RFC 4627 “The application/json Media Type for JavaScript Object Notation - (JSON)” , available at <http://tools.ietf.org/html/rfc4627>

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[6] Unicode Inc. (2010), Unicode Technical Report #15: “Unicode Normalization - Forms”, available at <http://www.unicode.org/reports/tr15/tr15-29.html>

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