JavaScript 模拟装饰者模式

/*** 抽象coffee父类，其实可以不用的*/
function Coffee () {}
Coffee.prototype.cost = function() {throw '实现这个方法';
};
/*** 黑咖啡，其实可以不用继承的；*/
function BlackCoffee () {}
// BlackCoffee.prototype = new Coffee();
// BlackCoffee.prototype.constructor = BlackCoffee;
BlackCoffee.prototype.cost = function() {return 1.99;
};
/*** 糖，其实可以不用继承的；*/
function Milk (coff) {this.coffee = coff;
}
// Milk.prototype = new Coffee();
// Milk.prototype.constructor = Milk;
Milk.prototype.cost = function() {return this.coffee.cost() + 0.2;
};
/*** 可以开店卖咖啡了；*/
var bc = new BlackCoffee();
var addMilk = new Milk(bc);
console.log(addMilk.cost());