1. function myPromise(constructor) {
    2.     let self = this;
    3.     self.status = "pending"; //定义状态改变前的初始状态
    4.     self.value = undefined; //定义状态为resolve的时候
    5.     self.reason = undefined; //定义状态为reject的时候
    7.     function resolve(value) {
    8.         if (self.status === "pending") {
    9.             self.value = value;
    10.             self.status === "resolved";
    11.         }
    12.     }
    14.     function reject(reason) {
    15.         if (self.status === "pending") {
    16.             self.reason = reason;
    17.             self.status === "rejected";
    18.         }
    19.     }
    21.     //捕获构造异常
    22.     try {
    23.         constructor(resolve, reject)
    24.     } catch (e) {
    25.         reject(e);
    26.     }
    27. }
    29. myPromise.prototype.then = function (onFullfilled, onRejected) {
    30.     let self = this;
    31.     switch (self.status) {
    32.         case "resolved":
    33.             onFullfilled(self.value);
    34.             break;
    35.         case "rejected":
    36.             onRejected(self.reason);
    37.             break;
    38.         default:
    39.     }
    40. }
    42. // // 测试代码
    43. // var p=new myPromise(function(resolve,reject){resolve(1)});
    44. // p.then(function(x){console.log(x)})
    45. // //输出1