创建一个异步的类

当任务函数执行next的时候，跳转到下一个任务函数
class Task {
  constructor() {
    this.taskIndex = 0
    this.taskList = []
    this.stopRun = false
  }
  add(fn,context, ...args) {
    const next = () => {
      this.taskIndex++
      if (!this.stopRun && this.taskList[this.taskIndex]) {
        this.run()
      }
    }
    this.taskList.push(fn.bind(context, next, ...args))
    return this
  }
  run() {
    this.taskList[this.taskIndex]()
  }
  stop() {
    this.stopRun = true
  }
}

function task1(next) {
  setTimeout(() => {
    console.log(1)
    next()
  },1000)
}

function task2(next,b) {
  setTimeout(() => {
    console.log(b)
    next()
  },1000)
}

let task = new Task()
task.add(task1).add(task2,null,3)
task.run()