在網(wǎng)上看到這么一道題：

這道題跟魚頭這篇記錄『什么是時間分片（Time Slicing）？ 』有點相似，但不同的是這次是限制異步并發(fā)的數(shù)量。

所以話不多說，我們先來康康實現(xiàn)

首先我們來實現(xiàn)一個分割數(shù)組的函數(shù)~

const group = (list = [], max = 0) => { if (!list.length) { return list } let results = [] for (let i = 0, len = list.length; i < len; i += max) { results.push(list.slice(i, i + max)) } return results}

這里就是根據(jù)指定的并發(fā)數(shù)量來分割數(shù)組。主要就是 for + slice ，這沒啥好說的

接下來我們再來一個用 async + await 實現(xiàn)的請求集合封裝。

我們通過 for...of 去遍歷每一個異步函數(shù)，然后用 async + await 確保函數(shù)的執(zhí)行順序，再用 try...catch 來保證即使 reject 報錯也不會導(dǎo)致無法繼續(xù)執(zhí)行任務(wù)。

const requestHandler = async ( groupedUrl = [], callback = () => { }) => { if (!groupedUrl.length) { callback() return groupedUrl } const newGroupedUrl = groupedUrl.map(fn => fn()) const resultsMapper = (results) => results.map(callback) const data = await Promise.allSettled(newGroupedUrl).then(resultsMapper) return data;}

接下來就是主函數(shù)

const sendRequest = async ( urls = [], max = 0, callback = () => { }) => { if (!urls.length) { return urls } const groupedUrls = group(urls, max) const results = [] console.log(’start !’) for (let groupedUrl of groupedUrls) { try { const result = await requestHandler(groupedUrl, callback) results.push(result) console.log(’go’) } catch { } } console.log(’done !’) return results}

這里就是利用了 for + async + await 來限制并發(fā)。等每次并發(fā)任務(wù)結(jié)果出來之后再執(zhí)行下一次的任務(wù)。

我們執(zhí)行下栗子：

const p1 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, ’p1’))const p2 = () => Promise.resolve(2)const p3 = () => new Promise((resolve, reject) => setTimeout(resolve, 2000, ’p3’))const p4 = () => Promise.resolve(4)const p5 = () => new Promise((resolve, reject) => setTimeout(reject, 2000, ’p5’))const p6 = () => Promise.resolve(6)const p7 = () => new Promise((resolve, reject) => setTimeout(resolve, 1000, ’p7’))const p8 = () => Promise.resolve(8)const p9 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, ’p9’))const p10 = () => Promise.resolve(10)const p11 = () => new Promise((resolve, reject) => setTimeout(resolve, 2000, ’p10’))const p12 = () => Promise.resolve(12)const p13 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, ’p11’))const p14 = () => Promise.resolve(14)const ps = [p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12, p13, p14]sendRequest(ps, 3, ({reason, value}) => { console.log(reason || value)})

OK，我們看到結(jié)果是如我們所愿的

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