Promise 面试常考手写方法汇总

前言

列举面试常考的Promise静态方法

1.Promise.all
2.Promise.allSettled
3.Promise.race
4.Promise.resolve
5.Promise.finally
6.Promise.catch

没涉及到的可评论补充，我更新文章

Promise.all

所有(异步/非异步)任务执行完，必须所有都成功

Promise.prototype.myAll = (array) => {let result = []let index = 0// 返回promise为了链式调用 return new Promise((resolve, reject) => {// 归纳数据方法function addData(key, value) {result[key] = valueif (++index === array.length) {resolve(result)}}// 遍历数组参数执行异步任务for(let i = 0; i < array.length; i++){let current = array[i]if (current instanceof Promise) {// promise 对象current.then(value => addData(i, value), reason => reject(reason))} else {// 普通值addData(i, array[i])}}})
} 
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Promise.allSettled

所有(异步/非异步)任务执行完，不管成功失败都输出，并且附带状态

Promise.prototype.myAllSettled = (array) => {let result = []let index = 0// 返回promise为了链式调用 return new Promise((resolve, reject) => {// 归纳数据方法function addData(key, status, value) {result[key] = {status, value}if (++index === array.length) {resolve(result)}}// 遍历数组参数执行异步任务for(let i = 0; i < array.length; i++){let current = array[i]if (current instanceof Promise) {// promise 对象current.then(value => {addData(i, 'fulfilled', value)}, reason => {addData(i, 'rejected', reason)})} else {// 普通值addData(i, 'fulfilled', array[i])}}})
} 
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Promise.race

输出(异步/非异步)任务执行最快的一个

Promise.prototype.myRace = (array) => {// 返回promise为了链式调用 return new Promise((resolve, reject) => {// 遍历数组参数执行异步任务for(let i = 0; i < array.length; i++){let current = array[i]if (current instanceof Promise) {// promise 对象current.then(value => resolve(value), reason => reject(reason))} else {// 普通值resolve(current)}}})
} 
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Promise.resolve

将给定的值转换为promise对象

Promise.prototype.myResolve = (value) => {if (value instanceof Promise) { return value;}return new Promise(reslove => reslove(value))
} 
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Promise.finally

不管promise成功还是失败，finally方法都会被调用借用then方法拿到promise链式调用结果

finally(callback) {return this.then(value => {return Promise.resolve(callback()).then(() => value)}, reason => {return Promise.resolve(callback()).then(() => { throw reason })})
} 
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Promise.catch

只需要借助then的失败回调

catch(failCallback){return this.then(undefined, failCallback)
} 
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…

基本覆盖常考点，大家需要可继续补充，求点一个赞！