JavaScript设计模式之责任链模式

适用场景：一个完整的流程，中间分成多个环节，各个环节之间存在一定的顺序关系，同时中间的环节的个数不一定，可能添加环节，也可能减少环节，只要保证顺序关系就可以。

如下图：

1. ES5写法

   const Chain = function (fn) {
   this.fn = fn
   this.nextChain = null
   this.setNext = function (nextChain) {
   this.nextChain = nextChain
   return this.nextChain
   }
   this.run = function () {
   this.fn()
   this.nextChain && this.nextChain.run()
   }
   }
   //申请设备
   const applyDevice = function () {
   console.log(111)
   }
   const chainApplyDevice = new Chain(applyDevice);
   //选择收货地址
   const selectAddress = function () {
   console.log(222)
   }
   const chainSelectAddress = new Chain(selectAddress);
   //选择审核人
   const selectChecker = function () {
   console.log(333)
   }
   const chainSelectChecker = new Chain(selectChecker);

   chainApplyDevice.setNext(chainSelectAddress).setNext(chainSelectChecker);
   chainApplyDevice.run(); //最后执行结果为111-222-333

2. ES6写法

   class Chain {
   constructor(fn) {
   this.fn = fn
   this.nextChain = null
   }
   setNext (nextChain) {
   this.nextChain = nextChain
   return this.nextChain
   }
   run() {
   this.fn()
   this.nextChain && this.nextChain.run()
   }
   }
   //申请设备
   const applyDevice = function () {
   console.log(111)
   }
   const chainApplyDevice = new Chain(applyDevice);
   //选择收货地址
   const selectAddress = function () {
   console.log(222)
   }
   const chainSelectAddress = new Chain(selectAddress);
   //选择审核人
   const selectChecker = function () {
   console.log(333)
   }
   const chainSelectChecker = new Chain(selectChecker);

   chainApplyDevice.setNext(chainSelectAddress).setNext(chainSelectChecker);
   chainApplyDevice.run(); //最后执行结果为111-222-333