Optimize JSON stringify by allowing QuoteJSONString to prefix with a comma.

src/json.js

 // Copyright 2009 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 175 matching lines @@
   }
   if (!%PushIfAbsent(stack, value)) {
     throw MakeTypeError('circular_structure', []);
   }
   builder.push("[");
   var val = value[0];
   if (IS_STRING(val)) {
     // First entry is a string. Remaining entries are likely to be strings too.
     builder.push(%QuoteJSONString(val));
     for (var i = 1; i < len; i++) {
-      builder.push(",");
       val = value[i];
       if (IS_STRING(val)) {
-        builder.push(%QuoteJSONString(val));
+        builder.push(%QuoteJSONStringComma(val));
       } else {
+        builder.push(",");
         var before = builder.length;
         BasicJSONSerialize(i, value[i], stack, builder);
-        if (before == builder.length) builder.push("null");
+        if (before == builder.length) builder[before - 1] = ",null";
       }
     }
   } else if (IS_NUMBER(val)) {
     // First entry is a number. Remaining entries are likely to be numbers too.
     builder.push(NUMBER_IS_FINITE(val) ? %_NumberToString(val) : "null");
     for (var i = 1; i < len; i++) {
       builder.push(",");
       val = value[i];
       if (IS_NUMBER(val)) {
         builder.push(NUMBER_IS_FINITE(val) 
                      ? %_NumberToString(val) 
                      : "null");
       } else {
         var before = builder.length;
         BasicJSONSerialize(i, value[i], stack, builder);
-        if (before == builder.length) builder.push("null");
+        if (before == builder.length) builder[before - 1] = ",null";
       }
     }
   } else {
     var before = builder.length;
     BasicJSONSerialize(0, val, stack, builder);
     if (before == builder.length) builder.push("null");
     for (var i = 1; i < len; i++) {
       builder.push(",");
       before = builder.length;
       val = value[i];
       BasicJSONSerialize(i, val, stack, builder);
-      if (before == builder.length) builder.push("null");
+      if (before == builder.length) builder[before - 1] = ",null";
     }
   }
   stack.pop();
   builder.push("]"); 
 }
 
 
 function BasicSerializeObject(value, stack, builder) {
   if (!%PushIfAbsent(stack, value)) {
     throw MakeTypeError('circular_structure', []);
   }
   builder.push("{");
+  var not_first = false;

[Erik Corry, 2011/01/14 14:42:57]

This variable should be called first and the boolean values should be inverted.

[sandholm, 2011/01/16 21:08:43]

Done.

   for (var p in value) {
     if (%HasLocalProperty(value, p)) {
-      builder.push(%QuoteJSONString(p));
+      if (not_first) builder.push(%QuoteJSONStringComma(p));

[Erik Corry, 2011/01/14 14:42:57]

multi-line if statements should use {}

[sandholm, 2011/01/16 21:08:43]

Done.

+      else builder.push(%QuoteJSONString(p));
       builder.push(":");
       var before = builder.length;
       BasicJSONSerialize(p, value[p], stack, builder);
       if (before == builder.length) {
         builder.pop();
         builder.pop();
       } else {
-        builder.push(",");
+        not_first = true;
       }
     }
   }
   stack.pop();
-  if (builder.pop() != ",") {
-    builder.push("{}");  // Object has no own properties. Push "{" back on.
-  } else {
-    builder.push("}");
-  }
+  builder.push("}");
 }
 
 
 function BasicJSONSerialize(key, value, stack, builder) {
   if (IS_SPEC_OBJECT(value)) {
     var toJSON = value.toJSON;
     if (IS_FUNCTION(toJSON)) {
       value = %_CallFunction(value, ToString(key), toJSON);
     }
   }
@@ skipping 58 matching lines @@
 }
 
 function SetupJSON() {
   InstallFunctions($JSON, DONT_ENUM, $Array(
     "parse", JSONParse,
     "stringify", JSONStringify
   ));
 }
 
 SetupJSON();