js18_reduce_for_prototype.js

/* 
 * (c) 2009 Takuto Wada; MIT License
 * JavaScript 1.8 compliant Array#reduce that also works with old prototype.js
 * usage: load this AFTER prototype.js
 */
(function () {

     // prototype.js's Array#reduce is removed since 1.6.1_rc2
     // see: http://github.com/sstephenson/prototype/commit/b34355653e1a663764fd8f69b4915f966c58cf55
     if (typeof Prototype !== 'undefined' && /^1\.(?:[0-5]\.\S+|6\.(?:0(?:\.\d)?|1_rc1))$/.test(Prototype.Version)) {

         var prototypeJsReduce = Array.prototype.reduce;

         // using Firefox's reduce implementation.
         // see: https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Objects/Array/reduce
         Array.prototype.reduce = function(fun /*, initial*/) {

             // modification: call prototype.js's Array#reduce if no arguments given
             if (arguments.length == 0)
                 return prototypeJsReduce.call(this);

             var len = this.length >>> 0;
             if (typeof fun != "function")
                 throw new TypeError();

             // no value to return if no initial value and an empty array
             if (len == 0 && arguments.length == 1)
                 throw new TypeError();

             var i = 0;
             var rv;
             if (arguments.length >= 2) {
                 rv = arguments[1];
             } else {
                 do {
                     if (i in this) {
                         rv = this[i++];
                         break;
                     }

                     // if array contains no values, no initial value to return
                     if (++i >= len)
                         throw new TypeError();
                 } while (true);
             }

             for (; i < len; i++) {
                 if (i in this)
                     rv = fun.call(null, rv, this[i], i, this);
             }

             return rv;
         };
     }
 })();