gistfile1.js

var Animal, Horse, Snake, sam, tom;
var __extends = function(child, parent) {
  var ctor = function(){ };
  ctor.prototype = parent.prototype;
  child.__superClass__ = parent.prototype;
  child.prototype = new ctor();
  child.prototype.constructor = child;
};
Animal = function() {
};
Animal.prototype.move = function(meters) {
  return console.log(this.name + " moved " + meters + "m.");
};
Animal.Mixin = function(self){
	var sex = "male";
	
	self.getSex = function(){
		return sex;
	}
	
	self.thinkThenMove = function(){
		console.log("thinking...");
		self.move();
	}
}

Snake = function(name) {
	new Animal.Mixin(this);
  this.name = name;
  return this;
};
__extends(Snake, Animal);
Snake.prototype.move = function() {
  console.log("Slithering...");
  return Snake.__superClass__.move.call(this, 5);
};

sam = new Snake("Sammy the snake");

// sam.sex => undefined
// sam.getSex => 'male'
// sam instanceof Animal => true
// sam instanceof Snake => true
// sam.thinkThenMove() => slithering...