JavaScript 数组映射 map

JavaScript 数组映射 map

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

   <body>

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

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

               var res = new Array(len);
               var thisp = arguments[1];

               for (var i = 0; i < len; i++) {
                  if (i in this)
                  res[i] = fun.call(thisp, this[i], i, this);
               }
               return res;
            };
         }

         var numbers = [1, 4, 9];
         var roots = numbers.map(Math.sqrt);
         document.write("roots is : " + roots );
      </script>

   </body>
</html>