封装原生promise函数

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>