封裝原生promise函數

時間 2020-07-06

原文原文鏈接

阿里面試題：html

手動封裝promise函數面試

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    /*
    *Promise實現思路
    * 1.構造函數
    * 2.回調函數的參數 resolve reject
    * 3.鏈式調用.then .catch
    */

    function PromiseM(cb){
        //初始狀態
        this.status = "pending";
        this.msg = "";

        cb((data)=>{
            this.status = "resolve";
            this.msg = data;
        },()=>{
            this.status = "reject";
        })
        return this;
    }

    //鏈式調用.then
    PromiseM.prototype.then = function(){
        var cb = arguments;

        //輪詢實現異步
        timer = setInterval(()=>{
            if(this.status == "resolve"){
                //成功狀態的回調
                cb[0](this.msg);
                clearInterval(timer);
            }else if(this.status == "reject"){
                //失敗狀態的回調
                cb[1](this.msg);
                clearInterval(timer);
            }
        },3000)
    }

    new PromiseM(function (resolve,reject){
        setTimeout(function (){
            console.log(1111);
            resolve('11111');/*reject也就是失敗時對應的函數，因爲這個例子比較簡單*/
        },1000)
    }).then(function (data){
        console.log("接收的值爲"+data);
    })

</script>
</body>
</html>

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