欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

模仿ES6的promise手写一个自己的promise

程序员文章站 2022-06-30 19:13:06
...

最近看了很多promise的特性和使用技巧,觉得挺好玩的;但是还是有些原理不清晰;
索性手写源码一下;看清原理

class Mypromise {
    constructor(handle) {
        this.status = 'pedding';//状态
        this.value = undefined;//结果
        this.resolveFn = [];
        this.rejectFn = [];
        handle(this._resolve.bind(this), this._reject.bind(this))
    }
    _resolve(val) {
        this.status = 'fulfilled';
        this.value = val;
        const run = () => {
            let cb;
            while (cb = this.resolveFn.shift()) {
                cb && cb(val)
            }
        }
        setTimeout(run);
    }
    _reject(val) {
        this.status = 'rejected';
        this.value = val;
        const run = () => {
            let cb;
            while (cb = this.rejectFn.shift()) {
                cb && cb(val)
            }
        }
        setTimeout(run);
    }
    then(onResolve, onReject) {
        return new Mypromise((resolve, reject) => {
            this.resolveFn.push(val => {
                let res = onResolve && onResolve(val)
                if (res instanceof Mypromise) {//如果是promise返回promise
                    return res.then(res => {
                        resolve(res)
                    })
                }
                resolve(res)
            })
            this.rejectFn.push(val => {
                let res =onReject && onReject(val)
                reject(res)
            })
        })
    }
    catch(onrejeted) {//catch方法
        this.then(undefined, onrejeted)
    }
    static resolve(val) {//promise.resolve()
        return new Mypromise(resolve => {
            resolve(val)
        })
    }
    static reject(val) {//promise.reject()
        return new Mypromise((resolve, reject) => {
            reject(val)
        })
    }
    static all(lists) {//promise.all()所有执行完成之后返回数组
        let arr=[]
        return new Mypromise((resolve, reject) => {
            lists.forEach(item => {
                item.then(res=>{
                    arr.push(res)
                    if(arr.length===lists.length){
                        resolve(arr)
                    }
                })
            });
        })
    }
    static arace(lists) {//promise.race()有一个执行完就返回
        return new Mypromise((resolve, reject) => {
            lists.forEach(item => {
                item.then(res=>{
                    resolve(res)
                },err=>{
                    reject(err)
                })
            });
        })
    }
    finally(cb) {//promise.finally()最后默认执行
        return this.then(res=>{
            cb()
        },err=>{
            cb()
        })
    }
}