1. es5 实现
    1. function log1() {
    2.     console.log("message 1")
    3. }
    4. function log2() {
    5.     console.log("message 2")
    6. }
    7. function log1() {
    8.     console.log("message 3")
    9. }
    11. function delay(fn, ms) {
    12.     var timer, self;
    13.   var queue
    14.   function schedule(fn, ms) {
    15.       timer = setTimeout(function() {
    16.         timer = null
    17.       fn()
    18.       if (queue.length) {
    19.           var item = queue.shift(item)
    20.         schedule(item.fn, item.ms)
    21.       } 
    22.     }, ms)
    23.   }
    25.   self = {
    26.       delay: function(fn, ms) {
    27.         if (queue,length || timer) {
    28.                queue.push({fn, ms})
    29.       } else {
    30.           schedule(fn, ms)
    31.       }
    32.       return self;
    33.     },
    34.     cancel: function() {
    35.         clearTimeout(timer)
    36.       queue = []
    37.     }
    38.   }
    39.     return self.delay(fn, ms)
    40. }
    42. var d = dalay(log1, 500).delay(log2, 1000).delay(log3, 2000)
    1. es6 实现
    1. function log1() {
    2.     console.log("message 1")
    3. }
    4. function log2() {
    5.     console.log("message 2")
    6. }
    7. function log1() {
    8.     console.log("message 3")
    9. }
    11. function delay(fn, ms) {
    12.     return new Promise(resolve => setTimeout(resolve, ms))
    13. }
    15. Promise.delay = function(fn, ms) {
    16.     // fn is optional
    17.   if (!ms) {
    18.       ms = fn
    19.     fn = function() {}
    20.   }
    22.   return delay(fn, ms).then(fn)
    23. }
    25. Promise.prototype.delay = function (fn, ms) {
    26.     return this.then(() => {
    27.       return Promise.delay(fn, ms)
    28.   })
    29. }
    31. Promise.delay(log1, 500).delay(log2, 2000).delay(log3, 3000);
    33. // 使用async/await 优化
    34. async queueTask() {
    35.     await Promise.delay(log1, 500)
    36.   await Promise.delay(log2, 1500)
    37.   await Promise.delay(log3, 2500)
    38. }
    39. queueTask()