Improved JSON stringify.

src/array.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 130 matching lines @@
       elements = new $Array(length << 1);
       for (var i = 0; i < length; i++) {
         var e = array[i];
         if (i != 0) elements[elements_length++] = separator;
         if (!IS_UNDEFINED(e) || (i in array)) {
           if (!IS_STRING(e)) e = convert(e);
           elements[elements_length++] = e;
         }
       }
     }
+    elements.length = elements_length;
+    var result = %_FastAsciiArrayJoin(elements, "");
+    if (!IS_UNDEFINED(result)) return result;
     return %StringBuilderConcat(elements, elements_length, '');
   } finally {
     // Make sure to pop the visited array no matter what happens.
     if (is_array) visited_arrays.pop();
   }
 }
 
 
 function ConvertToString(e) {
   if (e == null) return '';
@@ skipping 198 matching lines @@
 
 
 function ArrayJoin(separator) {
   if (IS_UNDEFINED(separator)) {
     separator = ',';
   } else if (!IS_STRING(separator)) {
     separator = ToString(separator);
   }
 
   var result = %_FastAsciiArrayJoin(this, separator);
-  if (typeof result != "undefined") return result;
+  if (!IS_UNDEFINED(result)) return result;
 
   var length = TO_UINT32(this.length);
   return Join(this, length, separator, ConvertToString);
 }
 
 
 // Removes the last element from the array and returns it. See
 // ECMA-262, section 15.4.4.6.
 function ArrayPop() {
   var n = TO_UINT32(this.length);
@@ skipping 788 matching lines @@
     "lastIndexOf", getFunction("lastIndexOf", ArrayLastIndexOf, 1),
     "reduce", getFunction("reduce", ArrayReduce, 1),
     "reduceRight", getFunction("reduceRight", ArrayReduceRight, 1)
   ));
 
   %FinishArrayPrototypeSetup($Array.prototype);
 }
 
 
 SetupArray();