text: export default class Schedule{
    constructor(){
      this._delay=0
      this.p = null
    }
    timer(task,ms){
      return new Promise((resolve,reject)=>{
        setTimeout(()=>{
          task && task()
          resolve()
        },ms)
      })
    }
    task(task){
      const {_delay:delay,timer,p}=this
      this.p = p ?p.then(()=>timer(task,delay)) :timer(task,delay)
      return this
    }
    delay(_delay){
      this._delay = _delay
      return this
    }
  }