x
 
<html>
<body>
<script type="text/javascript">
Array.prototype.indexOf = function (vItem) {
  for (var i=0; i < this.length; i++) {
    if (vItem == this[i]) {
      return i;
    }
  }
  return -1;
}
var aColors = new Array("red", "green", "blue");
document.write(aColors.indexOf("green"));
</script>
</body>
</html>