SOURCE

class _LazyMan {
    constructor(name){
      let that = this
      this.tasks = [],
      this.fn = ((n)=>{
            return ()=>{
              console.log("this is "+ n +"!(By Class)")
              that.next()
            }
          })(name)
      this.tasks.push(this.fn)
      setTimeout(() => {
        that.next()
      }, 0);
      return this
    }
  
    next(){
      var fn = this.tasks.shift()
      fn && fn()
    }
    
    eat(food){
      let fn = ((f)=>{
          return ()=>{
              console.log('eat '+ f)
              this.next()
          }
      })(food)
      this.tasks.push(fn);
      return this
    }

    sleep(delay,immedia = false){
        let that = this
        let fn = ((d,i)=>{
            return ()=>{
                setTimeout(()=>{
                    console.log(`${i ? 'sleepFisrt ' : 'sleep '}` + (d/1000) + 's')
                    that.next()
                },d)

            }
        })(delay,immedia)
        immedia ? this.tasks.unshift(fn) : this.tasks.push(fn);
        return this
    }

    sleepFirst(delay){
        return this.sleep(delay,true)
    }
}
  
let LazyMan = function (name){
    return new _LazyMan(name)
}
LazyMan('').eat('fish').sleepFirst(1000).sleep(2000)