promise实现方法 promise all

promise实现方法

function Promise(fn) {
    var value = null, succallbacks = [], failcallbacks = [];//成功执行方法集合  失败执行方法集合
    var status = "pending"; // 加入promise  3种状态
    this.then = function (fulfilled, rejected) {
        return new Promise(function(resolve,reject) {    //返回一个新的promise
            function suc(value) {   //成功
                var ret = typeof fulfilled === 'function' && fulfilled(value) || value;
                if( ret && typeof ret ['then'] == 'function'){    //判断 then中的 返回的是否是promise对象，如果是注册then方法
                    ret.then(function(value){
                        resolve(value);
                    });
                } else {
                    resolve(ret);
                }
            }
            function errback(reason) {  //失败
                reason = typeof rejected === 'function'  && rejected(reason) || reason;
                reject(reason);
            }

            if (status === 'pending') {
                succallbacks.push(suc);
                failcallbacks.push(errback);
            } else if(status === 'fulfilled'){
                suc(data);
            } else {
                errback(reason);
            }
        })

    }

    function resolve(value) {
        setTimeout(function () {   //加入延时
            status = "fulfilled";
            data = value;
            succallbacks.forEach((callback) => {
                callback(value);
            })
        }, 0)
    }

    function reject(value) {
        setTimeout(function () {
            status = "rejected";
            reason = value;
            failcallbacks.forEach((callback) => {
                callback(value);
            })

        }, 0)
    }

    fn(resolve, reject);
}

function fn(num) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve(num); //1   去掉time 则不会执行
        }, 1000)
    })
}

fn(1).then(data => {
        console.log(data);
        return 3 
        // new Promise((resolve,reject) => {    //then 方法返回的是一个promise对象，故执行 promise中的then注册该结果，在resolve
        //        setTimeout(() => { resolve(2);},1000)})
    }
).then(data=>{
    console.log(data);
});

promiseAll

function promiseAll(promises){
    return new Promise(function(resolve,reject){
        if(!Array.isArray(promises)){
            return reject(new TypeError("argument must be anarray"))
        }
        var countNum=0;
        var promiseNum=promises.length;
        var resolvedvalue=new Array(promiseNum);
        for(var i=0;i