1. function MyPromise(fn){
    2.     // 保存this指向
    3.   that = this;
    4.   // 初始化状态
    5.   that.status = "pending";
    6.   // value 用来保存最后的结果的
    7.   that.value = null;
    8.   fn(resolve, reject);
    9.   resolve = function(value) {
    10.       if(that.status === "pending") {
    11.         that.statue = "resolve";
    12.       that.value = value;
    13.     }
    14.   }
    15.   reject = function(value) {
    16.       if(that.status === "pending"){
    17.         that.value = value;
    18.     }
    19.   }
    20. }
    22. MyPromise.prototype.then = function (fn){
    23.   if(this.status === "resolve") {
    24.     fn(this.value);
    25.   }
    26. }
    28. let p = new MyPromise( (resolve, reject) => {
    29.     let num = Math.random()*100;
    30.   if(num<100){
    31.       resolve(num);
    32.   }else {
    33.       reject(num);
    34.   }
    35. } )
    37. p.then( res => console.log(res));