JavaScript 数组索引 indexof 方法

JavaScript 数组索引 indexof 方法

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

   <body>

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

               var from = Number(arguments[1]) || 0;
               from = (from < 0)
               ? Math.ceil(from)
               : Math.floor(from);

               if (from < 0)
               from += len;

               for (; from < len; from++) {
                  if (from in this &&
                  this[from] === elt)
                  return from;
               }
               return -1;
            };
         }

         var index = [12, 5, 8, 130, 44].indexOf(8);
         document.write("index is : " + index );

         var index = [12, 5, 8, 130, 44].indexOf(13);
         document.write("<br />index is : " + index );
      </script>

   </body>
</html>