Optimize JSON stringify for arrays.

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 166 matching lines @@
   return void 0;
 }
 
 
 function BasicSerializeArray(value, stack, builder) {
   if (!%PushIfAbsent(stack, value)) {
     throw MakeTypeError('circular_structure', []);
   }
   builder.push("[");
   var len = value.length;
-  for (var i = 0; i < len; i++) {
-    var before = builder.length;
-    BasicJSONSerialize(i, value, stack, builder);
-    if (before == builder.length) builder.push("null");
-    builder.push(",");
+  var val = value[0];

[Erik Corry, 2011/01/12 12:44:41]

what if len is 0 and value has an accessor on "0"?

[sandholm, 2011/01/12 13:36:20]

Good point. Fix uploaded. Could you have another look?

+  if (IS_STRING(val)) {
+    // First entry is a string. Remaining entries are likely to be strings too.
+    for (var i = 0; i < len; i++) {
+      val = value[i];
+      if (IS_STRING(val)) {
+        builder.push(%QuoteJSONString(val));
+      } else {
+        var before = builder.length;
+        BasicJSONSerialize(i, value, stack, builder);
+        if (before == builder.length) builder.push("null");
+      }
+      builder.push(",");
+    }
+  } else if (IS_NUMBER(val)) {
+    // First entry is a number. Remaining entries are likely to be numbers too.
+    for (var i = 0; i < len; i++) {
+      val = value[i];
+      if (IS_NUMBER(val)) {
+        builder.push(NUMBER_IS_FINITE(val) 
+                     ? %_NumberToString(val) 
+                     : "null");
+      } else {
+        var before = builder.length;
+        BasicJSONSerialize(i, value, stack, builder);
+        if (before == builder.length) builder.push("null");
+      }
+      builder.push(",");
+    }
+  } else {
+    for (var i = 0; i < len; i++) {
+      var before = builder.length;
+      BasicJSONSerialize(i, value, stack, builder);
+      if (before == builder.length) builder.push("null");
+      builder.push(",");
+    }
   }
   stack.pop();
   if (builder.pop() != ",") {
     builder.push("[]");  // Zero length array. Push "[" back on.
   } else {
     builder.push("]");
   }
 
 }
 
@@ skipping 95 matching lines @@
 }
 
 function SetupJSON() {
   InstallFunctions($JSON, DONT_ENUM, $Array(
     "parse", JSONParse,
     "stringify", JSONStringify
   ));
 }
 
 SetupJSON();