// The base Class implementation (does nothing)

this.Class = function(){};

// Create a new Class that inherits from this class

Class.extend = function(prop) {

var _super = this.prototype;
// Instantiate a base class (but only create the instance,// don't run the init constructor)
initializing = true;
var prototype = new this();
initializing = false;

// Copy the properties over onto the new prototype
for (var name in prop) {
  // Check if we're overwriting an existing function
  prototype[name] = typeof prop[name] == "function" &&
    typeof _super[name] == "function" && fnTest.test(prop[name]) ?
    (function(name,fn){
      return function() {
        var tmp = this._super;

        // Add a new ._super() method that is the same method
        // but on the super-class
        this._super = _super[name];
        // this._super = function(){
        //   console.log('call super method');
        // }

        // The method only need to be bound temporarily,so we
        // remove it when we're done executing
        var ret = fn.apply(this,arguments);        
        this._super = tmp;

        return ret;
      };
    })(name,prop[name]) :
    prop[name];
}

// The dummy class constructor
function Class() {
  // All construction is actually done in the init method
  if ( !initializing && this.init )
    this.init.apply(this,arguments);
}

// Populate our constructed prototype object
Class.prototype = prototype;

// Enforce the constructor to be what we expect
Class.prototype.constructor = Class;

// And make this class extendable
Class.extend = arguments.callee;

return Class;
};

})();
var Person = Class.extend({

init: function(isDancing){

this.dancing = isDancing;

},dance: function(){

return this.dancing;

}

});
var Ninja = Person.extend({

init: function(){

this._super( false );

},dance: function(){

// Call the inherited version of dance()

return this._super();

},swingSword: function(){

return true;

}

});
var p = new Person(true);

p.dance(); // => true
var n = new Ninja();

n.dance(); // => false

n.swingSword(); // => true
// Should all be true

p instanceof Person && p instanceof Class &&

n instanceof Ninja && n instanceof Person && n instanceof Class