extend.js

var  __hasProp = {}.hasOwnProperty,
    __extends = function(child, parent) {
      for (var key in parent) {
           if (__hasProp.call(parent, key))
                child[key] = parent[key];
      }

      function ctor() {
           this.constructor = child;
      }
      ctor.prototype = parent.prototype;
      child.prototype = new ctor();
      child.__super__ = parent.prototype;
      return child;
};

Animal = (function() {

 function Animal(name) {
   this.name = name;
 }

 Animal.prototype.move = function(meters) {
   console.log(this.name + (" moved " + meters + "m."));
 };

 return Animal;

})();

Snake = (function(_super) {

 __extends(Snake, _super);

 function Snake() {
   return Snake.__super__.constructor.apply(this, arguments);
 }

 Snake.prototype.move = function() {
   console.log("Slithering...");
   return Snake.__super__.move.call(this, 5);
 };

 return Snake;

})(Animal);


Horse = (function(_super) {

 __extends(Horse, _super);

 function Horse() {
   return Horse.__super__.constructor.apply(this, arguments);
 }

 Horse.prototype.move = function() {
   console.log("Galloping...");
   return Horse.__super__.move.call(this, 45);
 };

 return Horse;

})(Animal);

new Snake("snake").move();
new Horse("horse").move()