Array.join() is really slow and has array memory allocation overhead... inste...

src/string.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 70 matching lines @@
   }
   var subject = ToString(this);
   var index = TO_INTEGER(pos);
   return %StringCharCodeAt(subject, index);
 }
 
 
 // ECMA-262, section 15.5.4.6
 function StringConcat() {
   var len = %_ArgumentsLength();
-  var parts = new $Array(len + 1);
-  parts[0] = ToString(this);
-  for (var i = 0; i < len; i++)
-    parts[i + 1] = ToString(%_Arguments(i));
-  return parts.join('');
+  var this_string = ToString(this);

[Christian Plesner Hansen, 2009/10/02 05:47:12]

I would suggest using %StringAdd if len == 1 and using a StringBuilder (se
string.js) if there are more arguments.  That way the result becomes a flat
string rather than a chain of conses which we will have to flatten later.

+  for (var i = 0; i < len; i++) {
+    this_string = %StringAdd(this_string, ToString(%_Arguments(i)));
+  }
+  return this_string;
 }
 
 // Match ES3 and Safari
 %FunctionSetLength(StringConcat, 1);
 
 
 // ECMA-262 section 15.5.4.7
 function StringIndexOf(searchString /* position */) {  // length == 1
   var subject_str = ToString(this);
   var pattern_str = ToString(searchString);
@@ skipping 761 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();