Ninja.js

var Ninja = new Class({ 
  Extends: Human, 
  Implements: [Warrior], 
  initialize: function(side, name, age){
    this.side = side; 
    this.parent(name, age);
  } 
});

var blackNinja = new Ninja('evil', 'Nin Tendo', 'unknown');
blackNinja.eat(); // inherited from Human
blackNinja.attack(bob); // copied from Warrior
bob.isAlive; // false, bob never had a chance
blackNinja.kills; // 1, from Warrior