阿里面试题：
手动封装promise函数
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> </head> <body> <script> /* *Promise实现思路 * 1.构造函数 * 2.回调函数的参数 resolve reject * 3.链式调用.then .catch */ function PromiseM(cb){ //初始状态 this.status = "pending"; this.msg = ""; cb((data)=>{ this.status = "resolve"; this.msg = data; },()=>{ this.status = "reject"; }) return this; } //链式调用.then PromiseM.prototype.then = function(){ var cb = arguments; //轮询实现异步 timer = setInterval(()=>{ if(this.status == "resolve"){ //成功状态的回调 cb[0](this.msg); clearInterval(timer); }else if(this.status == "reject"){ //失败状态的回调 cb[1](this.msg); clearInterval(timer); } },3000) } new PromiseM(function (resolve,reject){ setTimeout(function (){ console.log(1111); resolve('11111');/*reject也就是失败时对应的函数，由于这个例子比较简单*/ },1000) }).then(function (data){ console.log("接收的值为"+data); }) </script> </body> </html>