"Extending" a native JavaScript "class"

reverse.js

<script>
(function(){
  
  // http://webreflection.blogspot.com/2008/10/subclassing-javascript-native-string.html

  function MyString(__value__) {
    this.length = (this.__value__ = __value__ || "").length;
  };
  with(MyString.prototype = new String)
      toString = valueOf = function() { return this.__value__ };
  MyString.prototype.reverse = function() {
    var r = "";
    for (i = this.__value__.length - 1; i >= 0; i--) {
      r = r + this.__value__[i];
    };
    return r;
  };

  window.$ = function(s) {
    return new MyString(s);
  };

})();
</script>

<script>
alert($("!desreveR").reverse());
</script>