简单中间件的实现

简易版实现中几点必须的操作：

• 一个array middleList 来存储中间件
• 执行中间件的操作，循环 middleList 将每一项执行，或者使用shift 将切出的每一项执行
• 有next 、 done 函数
• 初始执行next

class MiddleWare {
  constructor(data) {
    this.data = data;
    this.middleList = [];
    this.next = this.next.bind(this)
    this.done = this.done.bind(this)
  }
  use(middle) {
    if (typeof middle !== 'function') {
      throw 'middle is not a function'
      return;
    }
    this.middleList.push(middle)
  }
  next() {
    if (this.middleList.length > 0) {
      let cur = this.middleList.shift();
      cur(this.data, this.next, this.done)
    } else {
      this.done()
    }
  }
  done() {
    this.middleList = [];
    console.log('全部执行完毕');
  }
}


const fn1 = (data, next, done) => {
  console.log('this is fn1', data);
  setTimeout(() => {
    next();
  }, 2000);
}
const fn2 = (data, next, done) => {
  console.log('this is fn2', data);
  // done()
  next();
}
const fn3 = (data, next, done) => {
  console.log('this is fn3', data);
  next();
}

const data = '123'
// 传入参数
let list = new MiddleWare(data);
list.use(fn1)
list.use(fn2)
list.use(fn3)
list.next()