Some string optimizations:

src/runtime.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 511 matching lines @@
 
 // ECMA-262, section 9.8, page 35.
 function ToString(x) {
   if (IS_STRING(x)) return x;
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   if (IS_UNDEFINED(x)) return 'undefined';
   return (IS_NULL(x)) ? 'null' : %ToString(%DefaultString(x));
 }
 
+function NonStringToString(x) {
+  if (IS_NUMBER(x)) return %NumberToString(x);
+  if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
+  if (IS_UNDEFINED(x)) return 'undefined';
+  return (IS_NULL(x)) ? 'null' : %ToString(%DefaultString(x));
+}
+
 
 // ECMA-262, section 9.9, page 36.
 function ToObject(x) {
   if (IS_STRING(x)) return new $String(x);
   if (IS_NUMBER(x)) return new $Number(x);
   if (IS_BOOLEAN(x)) return new $Boolean(x);
   if (IS_NULL_OR_UNDEFINED(x) && !IS_UNDETECTABLE(x)) {
     throw %MakeTypeError('null_to_object', []);
   }
   return x;
@@ skipping 90 matching lines @@
   throw %MakeTypeError('cannot_convert_to_primitive', []);
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essiential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));