JavaScript 数组 reduce 方法

JavaScript 数组 reduce 方法

<html>
   <head>
      <title>JavaScript Array reduce Method</title>
   </head>

   <body>

      <script type = "text/javascript">
         if (!Array.prototype.reduce) {
            Array.prototype.reduce = function(fun /*, initial*/) {
               var len = this.length;

               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;
               if (arguments.length >= 2) {
                  var 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;
            };
         }

         var total = [0, 1, 2, 3].reduce(function(a, b){ return a + b; });
         document.write("total is : " + total );
      </script>

   </body>
</html>