From 522566ea80011dc1674ca7f10a5666a24f24ac27 Mon Sep 17 00:00:00 2001
From: Richard Gibson <richard.gibson@gmail.com>
Date: Wed, 23 Jan 2013 23:52:04 -0500
Subject: [PATCH] Fix #105: property comparison to undefined is not always safe

---
 lib/compress.js            |  3 ++-
 test/compress/issue-105.js | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 test/compress/issue-105.js

diff --git a/lib/compress.js b/lib/compress.js
index 982b2b19..bc0b9ee5 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1739,7 +1739,8 @@ merge(Compressor.prototype, {
             if (self.left instanceof AST_String
                 && self.left.value == "undefined"
                 && self.right instanceof AST_UnaryPrefix
-                && self.right.operator == "typeof") {
+                && self.right.operator == "typeof"
+                && compressor.option("unsafe")) {
                 if (!(self.right.expression instanceof AST_SymbolRef)
                     || !self.right.expression.undeclared()) {
                     self.left = self.right.expression;
diff --git a/test/compress/issue-105.js b/test/compress/issue-105.js
new file mode 100644
index 00000000..349d732d
--- /dev/null
+++ b/test/compress/issue-105.js
@@ -0,0 +1,17 @@
+typeof_eq_undefined: {
+    options = {
+        comparisons: true,
+        unsafe: false
+    };
+    input: { a = typeof b.c != "undefined" }
+    expect: { a = "undefined" != typeof b.c }
+}
+
+typeof_eq_undefined_unsafe: {
+    options = {
+        comparisons: true,
+        unsafe: true
+    };
+    input: { a = typeof b.c != "undefined" }
+    expect: { a = b.c !== void 0 }
+}
-- 
2.34.1