装饰器模式

向预定义对象中添加功能，从而在运行时可以调整对象。

实现方式：

1. 原型链

    function Sale(price) {
        this.price = price || 100;
    }
    Sale.prototype.getPrice = function () {
        return this.price;
    };
    Sale.prototype.decorate = function(decorate){
        var F = function(){}, overrides = this.constructor.decorators[decorate], i,newobj;
        F.prototype = this;
        newobj = new F();
        newobj.uber = F.prototype;
        for(i in overrides){
            if (overrides.hasOwnProperty(i)){
                newobj[i] = overrides[i];
            }
        }
        return newobj;
    };
   
    Sale.decorators = {};
   
    Sale.decorators.fedtax = {
        getPrice: function () {
            var price = this.uber.getPrice();
            price += price * 5 / 100;
            return price;
        }
    };
   
    Sale.decorators.quebec = {
        getPrice: function () {
            var price = this.uber.getPrice();
            price += price * 7.5 / 100;
            return price;
        }
    };
   
    Sale.decorators.money = {
        getPrice: function () {
            return '$' + this.uber.getPrice().toFixed(2);
        }
    };
   
    Sale.decorators.cdn = {
        getPrice: function () {
            return 'CDN$' + this.uber.getPrice().toFixed(2);
        }
    };
   
    // usage
    var sale = new Sale(100);
    sale = sale.decorate('fedtax');
    sale = sale.decorate('quebec');
    sale = sale.decorate('money');
    console.log(sale.getPrice());
   

1. 列表（将前一个方法的结果传递到下一个方法里）

    function Sale(price) {
        this.price = price || 100;
        this.decorators_list = [];
    }
   
    Sale.decorators = {};
   
    Sale.decorators.fedtax = {
        getPrice: function (price) {
            price += price * 5 / 100;
            return price;
        }
    };
   
    Sale.decorators.quebec = {
        getPrice: function (price) {
            price += price * 7.5 / 100;
            return price;
        }
    };
   
    Sale.decorators.money = {
        getPrice: function (price) {
            return '$' + price.toFixed(2);
        }
    };
   
    Sale.prototype.decorate = function (decorator) {
        this.decorators_list.push(decorator);
    };
   
    Sale.prototype.getPrice = function () {
        var price = this.price, i, max = this.decorators_list.length, name;
        for (i = 0; i < max; i++) {
            name = this.decorators_list[i];
            price = Sale.decorators[name].getPrice(price);
        }
        return price;
    };
   
    // usage
    var sale = new Sale(100);
    sale.decorate('fedtax');
    sale.decorate('quebec');
    sale.decorate('money');
    console.log(sale.getPrice());