JavaScript 数组 reduceRight 方法

JavaScript 数组 reduceRight 方法

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

   <body>

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

               if (typeof fun != "function")
               throw new TypeError();

               // no value to return if no initial value, empty array
               if (len == 0 && arguments.length == 1)
               throw new TypeError();
               var i = len - 1;

               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 < 0)
                     throw new TypeError();
                  }
                  while (true);
               }
               for (; i >= 0; i--) {
                  if (i in this)
                  rv = fun.call(null, rv, this[i], i, this);
               }
               return rv;
            };
         }

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

   </body>
</html>