本篇文章和大家看看JavaScript如何處理并行請(qǐng)求？介紹一下JS處理并行請(qǐng)求的四種方式，希望對(duì)大家有所幫助！

需求

兩個(gè)異步請(qǐng)求同時(shí)發(fā)出，兩個(gè)請(qǐng)求都返回時(shí)再做處理

實(shí)現(xiàn)

這里的方法僅提供思路，只做請(qǐng)求成功處理

方法一

使用Promise.all

const startTime = new Date().getTime() function request(time) {   return new Promise(resolve => {     setTimeout(() => {       resolve(time)     }, time)   }) } let request1 = request(3000) let request2 = request(2000) Promise.all([request1, request2]).then(res => {   console.log(res, new Date() - startTime)	// [ 3000, 2000 ] 3001 })

方法二

自定義狀態(tài)，在回調(diào)中判斷返回狀態(tài)，待2個(gè)請(qǐng)求都有返回值時(shí)再做處理

const startTime = new Date().getTime() function request(time) {   return new Promise(resolve => {     setTimeout(() => {       resolve(time)     }, time)   }) } let state = [undefined, undefined] let request1 = request(3000) let request2 = request(2000) request1.then(res => {   state[0] = res   process() }) request2.then(res => {   state[1] = res   process() }) function process() {   if (state[0] && state[1]) {     console.log(state, new Date() - startTime) // [ 3000, 2000 ] 3001   } }

方法三

generator，yield

const startTime = new Date().getTime() function ajax(time, cb) {   setTimeout(() => cb(time), time) } function request(time) {   ajax(time, data => {     it.next(data);   }) } function* main() {   let request1 = request(3000);   let request2 = request(2000);   let res1 = yield request1   let res2 = yield request2   console.log(res1, res2, new Date() - startTime) // 2000 3000 3001 } let it = main(); it.next();

這個(gè)地方有點(diǎn)問題，因?yàn)閞equest2耗時(shí)較短，會(huì)先返回，也就是先執(zhí)行it.next(2000)，導(dǎo)致res1獲得了request2的返回值若使用co函數(shù)，則不會(huì)存在這個(gè)問題，因?yàn)閏o是在promise.then函數(shù)中才執(zhí)行it.next()，相當(dāng)于it.next()是鏈?zhǔn)秸{(diào)用

generator使用co函數(shù)

const co = require('co') const startTime = new Date().getTime() function request (time) {   return new Promise(resolve => {     setTimeout(() => {       resolve(time)     }, time)   }) } co(function* () {   let request1 = request(3000);   let request2 = request(2000);   let res1 = yield request1   let res2 = yield request2   console.log(res1, res2, new Date() - startTime) // 3000 2000 3001 })

有了co函數(shù)，就不需要生成it和執(zhí)行next方法了； co的原理其實(shí)也簡(jiǎn)單，就是遞歸執(zhí)行next，直到done為true； 如果next返回的value是Promise，則在then函數(shù)中執(zhí)行next，若不是Promise，直接執(zhí)行next函數(shù) 下面是co函數(shù)的簡(jiǎn)版手寫實(shí)現(xiàn)

function co(func) {   let it = func()   let t = it.next()   next()      function next() {     if (t.done) return     if (t.value instanceof Promise) {       t.value.then(res => {         t = it.next(res)         next()       })     } else {       t = it.next(t.value)       next()     }   } }

方法四

有了generator，很容易想到async/await，畢竟async/await就是由generator實(shí)現(xiàn)的

// setTimeout模擬異步請(qǐng)求，time為請(qǐng)求耗時(shí) const startTime = new Date().getTime() function request (time) {   return new Promise(resolve => {     setTimeout(() => {       resolve(time)     }, time)   }) } (async function () {   let request1 = request(3000)   let request2 = request(2000)   let res1 = await request1   console.log(res1, new Date() - startTime)	// 3000 3001   let res2 = await request2   console.log(res2, new Date() - startTime) // 2000 3005 })()