SOURCE

 class LazyMan {
     constructor(attr){
         console.log(`I am ${attr}`)
         this.cb = [] // 用于存放回调函数
         setTimeout(() => {
             this.runCb()
         },0)
     }
     sleep(num){
         let that = this
         let fn = (function(n){
             return function(){
                 setTimeout(() => {
                    console.log(`等了${n}秒`)
                    that.runCb()
                },n)
             }
         })(num)
         this.cb.push(fn)
         return this
     }
     sleepFirst(num){
         let that = this
         let fn = (function(n){
             return function(){
                 setTimeout(() => {
                     console.log(`wating ${n} 秒`)
                     that.runCb()
                 },n)
             }
         })(num)

         this.cb.unshift(fn)
         return this
     }
     runCb(){
         let fn = this.cb.shift()
         fn && fn()
     }
     eat(attr){
         let that = this
         let fn = (function(str){
             return function(){
                 console.log(`I am eating ${str}`)
                 that.runCb()
             }
         })(attr)
         this.cb.push(fn)
         return this
     }

 }

new LazyMan('Tom').eat('brunch').eat('tea').sleepFirst(2000)