简单封装Promise，Promise.all，Promise.race

最新推荐文章于 2024-04-08 20:15:46 发布

jack wang666

最新推荐文章于 2024-04-08 20:15:46 发布

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本文链接：https://blog.youkuaiyun.com/qq_43487823/article/details/114851114

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简单封装Promise，Promise.all，Promise.race

1.封装Promise

class MyPromise {
    constructor(fn){

        //在未调用resolve活着reject之前使用then
        this.resolvedCallbacks = [];
        this.rejectedCallbacks = [];

        this.state = 'PENDING';//等待状态
        this.value = '';

        fn(this.resolve.bind(this),this.reject.bind(this));
    }
    resolve(value){
        if(this.state === 'PENDING'){
            this.state = 'RESOLVED';//解决状态
            this.value = value;

            this.resolvedCallbacks.map(cb => cb(value));
        }

    }
    reject(value){
        if(this.state === 'PENDING'){
            this.state = 'REJECTED';//拒绝状态
            this.value = value;

            this.rejectedCallbacks.map(cb => cb(value));
        }
    }
    then(onFullfilled,onRejected){
        if(this.state === 'PENDING'){
            this.resolvedCallbacks.push(onFullfilled);
            this.rejectedCallbacks.push(onRejected);
        }
        else if(this.state === 'RESOLVED'){
            onFullfilled(this.value);
        }
        else if(this.state === 'REJECTED'){
            onRejected(this.value);
        }
    }
}

2.封装Promise.all

function PromiseAll(promises){
    if(!Array.isArray(promises)){
        throw new Error('promises must be an array');
    }
    return new Promise((resolve,reject)=>{
        let promiseNum = promises.length;
        let resolvedCount = 0; //记录解决的数量
        let resolvedValues = new Array(promiseNum);
        for(let i=0; i<promiseNum; i++){
            Promise.resolve(promises[i]).then(function(value) {
                resolvedValues[i] = value;
                resolvedCount++;
                if(resolvedCount === promiseNum){
                    return resolve(resolvedValues);
                }
            }, function(reason){
                return reject(reason);
            })
        }
    })
}

3.封装Promise.race

function PromiseRace(promises){
    if(!Array.isArray(promises)){
        throw new Error('promises must be an Array');
    }
    return new Promise((resolve,reject)=>{
        promises.forEach(p => {
            Promise.resolve(p).then(function(value){
                resolve(value);
            }, function(reason){
                reject(reason);
            })
        })
    })
}