Chain Of Responsibility Design Pattern (javascript)

Posted at 2016-04-15 Chain Of Responsibility design pattern 

使用情境

Chain Of Responsibility 主要用在順序可能會變換，甚至不確定要執行全部的步驟或只有部分的步驟。你會非常常見到它或許名稱不同，pipeline 或 middleware，都具有到這樣的概念。

案例

在這個例子，主要是針對具有很多種類的促銷方案，你同時有多種折扣，你希望它的計算順序可以很輕易的更變。

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var DiscountService = {
	order: null,
  init:function (order) {
    this.order = order;
		return this;
	},
  // 特定分類折扣
	dptDiscount:function () {
    this.order.price = Math.round(this.order.price * 0.9);
    return this;
	},
  // 滿額折扣
	bigOrderDiscount:function () {
    if(this.order.price > 6000){
      this.order.price -= 100;
    }
		return this;
	},
  // VIP 折扣
	vip:function () {
    if(this.order.isVip){
      this.order.price = Math.round(this.order.price * 0.95);
    }
		return this;
	}
};

module.exports = DiscountService;

進入點

main.js

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var DiscountService = require('./DiscountService.js');

var order = {
  isVip: true,
  price: 1000
}

var result = DiscountService.init(order).dptDiscount().bigOrderDiscount().vip();
console.log('price is $', result.order.price);

var order2 = {
  isVip: true,
  price: 6600
}

var result2 = DiscountService.init(order2).dptDiscount().bigOrderDiscount().vip();
console.log('price is $', result2.order.price);

var result3 = DiscountService.init(order2).dptDiscount().vip().bigOrderDiscount();
console.log('price is $', result3.order.price);


var result4 = DiscountService.init(order2).dptDiscount().vip();
console.log('price is $', result4.order.price);