实现洋葱模型

[Inchill]

// 写一个 Task 类
 
class Task {
  constructor() {
    // coding here
    this.queue = []
    this.flag = false
  }

  add(fn, context, ...args) {
    // coding here
    let task = {
      fn,
      context,
      args: [...args]
    }
    this.queue.push(task)
    return this
  }

  run() {
    // coding here
    let len = this.queue.length

    const func = (index = 0) => {
      if (this.flag) return Promise.reject(new Error('Follow-up tasks are stopped.'))
      if (index === len) return Promise.resolve()

      const task = this.queue[index]
      return Promise.resolve(task.fn.apply(task.context, [() => func(++index), ...task.args]))
    }

    return func()
  }

  stop() {
    // coding here
    // this.queue = []
    this.flag = true
  }
}


// 满足

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

function task2(next, a) {
  // this.stop()
  console.log(this.queue)
  setTimeout(() => {
    console.log(a)
    next()
  }, 1000)
}

function task3(next, b, c) {
  setTimeout(() => {
    console.log(b)
    console.log(c)
    next()
  }, 1000)
}

const task = new Task()
task.add(task1).add(task2, task, 2).add(task3, task, 3, 4)
task.run()


// 备注：当任务函数执行 next 的时候，会跳转到下一个任务函数执行