设计模式-javascript实现【职责链模式】

定义：使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系，将这些对象连成
一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

1. 实现职责链

// 定义职责链
class Chain {
  constructor(fn){
    this.fn = fn;
    this.successor = null;
  }
  // 设置下一个节点
  setNextSuccessor(successor){
    return this.successor = successor;
  }
  // 传递或者执行请求
  passRequest(){
    const ret = this.fn.apply(this, arguments);
    if(ret === 'nextSuccessor'){
      return this.successor && this.successor.passRequest.apply(this.successor, arguments);
    }
    return ret;
  }
  // 异步职责链可以直接调用next方法
  next(){
    return this.successor && this.successor.passRequest.apply(this.successor, arguments);
  }
}

// 定义职责链上的节点
const order500 = function(orderType, pay, stock){
  if(orderType === 1 && pay === true){
    console.log('500元定金预购，得到100元优惠券');
  }
  else {
    return 'nextSuccessor';
  }
}

const order200 = function(orderType, pay, stock){
  if(orderType === 2 && pay === true){
    console.log('200元定金预购，得到50元优惠券');
  }
  else {
    return 'nextSuccessor';
  }
}

const orderNormal = function(orderType, pay, stock){
  if(stock > 0) {
    console.log('普通购买');
  }
  else {
    console.log('手机库存不足');
  }
}
// 职责链设置和调用
const chainOrder500 = new Chain(order500);
const chainOrder200 = new Chain(order200);
const chainOrderNormal = new Chain(orderNormal)
chainOrder500.setNextSuccessor(chainOrder200).setNextSuccessor(chainOrderNormal);
chainOrder500.passRequest(3, true, 500);

/** 异步职责调用 **/
const fn1 = new Chain(function(){
  console.log(1);
  return 'nextSuccessor';
});
const fn2 = new Chain(function(){
  console.log(2);
  const self = this;
  setTimeout(function(){
    self.next();
  }, 1000);
});
const fn3 = new Chain(function(){
  console.log(3);
});
fn1.setNextSuccessor(fn2).setNextSuccessor(fn3);
fn1.passRequest();

2. 用AOP实现职责链

// 定义函数链
Function.prototype.after = function(fn){
  const self = this;
  return function(){
    const ret = self.apply(this, arguments);
    if(ret === 'nextSuccessor'){
      return fn.apply(this, arguments);
    }
    return ret;
  };
}

// 定义函数节点
const order500 = function(orderType, pay, stock){
  if(orderType === 1 && pay === true){
    console.log('500元定金预购，得到100元优惠券');
  }
  else {
    return 'nextSuccessor';
  }
}

const order200 = function(orderType, pay, stock){
  if(orderType === 2 && pay === true){
    console.log('200元定金预购，得到50元优惠券');
  }
  else {
    return 'nextSuccessor';
  }
}

const orderNormal = function(orderType, pay, stock){
  if(stock > 0) {
    console.log('普通购买');
  }
  else {
    console.log('手机库存不足');
  }
}
const order = order500.after(order200).after(orderNormal);
order(2, true, 500);