Extends a function object used as a class Constructor

extend.js

var extend = function(obj) {
    var args = Array.prototype.slice.call(arguments, 1);

    for (var i = 0, len = args.length; i < len; i++) {
      for (var prop in args[i]) {
        obj[prop] = args[i][prop];
      }
    }
};

NAMESPACE.extend = function(protoProperties) {
    var parent = this;
    var child = function(){ return parent.apply(this, arguments); };
    
    // Extend static properties to the constructor function
    extend(child, parent);

    // Set the prototype chain to inherit from `parent`, without calling
    // `parent`'s constructor function.
    var Dummy = function(){ this.constructor = child; };
    Dummy.prototype = parent.prototype;
    child.prototype = new Dummy();

    // Extend the child's prototype
    extend(child.prototype, protoProperties);

    // Set a property to point to the parent's prototype
    child.__super__ = parent.prototype;

    return child;
  };