1，最大并行请求数固定，比如2个，方案是记录当前并行的数量curcount，利用递归持续发出请求
1 class asyncPromise { 2 constructor() { 3 this.maxcount = 2 // 最大数 4 this.curcont = 0 // 当前请求数 5 this.promiseArr = [] 6 } 7 8 taskStart() { 9 if (!this.promiseArr.length) { 10 return false 11 } 12 for (let i = 0; i < this.maxcount; i++) { 13 this.start() 14 } 15 } 16 17 start() { 18 if (this.curcont > this.maxcount) { 19 return false 20 } 21 console.log(this.curcont, ‘322‘) 22 this.curcont++; 23 let p = this.promiseArr.pop() 24 p && p.then((res) => { 25 this.curcont-- 26 this.start() // 递归 27 }) 28 } 29 30 addPromise(p) { 31 this.promiseArr.push(p) 32 } 33 }
1 const synchronousFile = function (id) { 2 console.log(id) 3 } 4 const proxySynchronousFile = (function () { 5 let cache = [], 6 timer = null 7 return function (id) { 8 cache.push(id) 9 if (timer) { 10 return false 11 } 12 timer = setTimeout(() => { 13 synchronousFile(cache.join(‘,‘)) 14 clearTimeout(timer) 15 timer = null 16 cache = [] 17 }, 2000) 18 } 19 })();
// 方案1
1 Promise.allSettled = function (promiseArr) { 2 return new Promise((resolve, reject) => { 3 const len = promiseArr.length, 4 resArr = [] 5 for (let i = 0; i < len; i++) { 6 promiseArr[i].then((res) => { 7 resArr.push(res) 8 console.log(i, ‘ddddddd‘) 9 }).catch((err) => { 10 resArr.push(err) 11 }).finally(() => { 12 if (len === i + 1) { 13 resolve(resArr) 14 } 15 }) 16 } 17 }) 18 }
方案二是利用Promise.all，将Promise.all的运行的promise包一层，将其全部返回正确的onFulfilled状态
1 const rejectHandler = reason => ({ 2 status: "rejected", 3 reason 4 }) 5 const resolveHandler = value => ({ 6 status: "fulfilled", 7 value 8 }) 9 Promise.allSettled = promises => 10 Promise.all( 11 promises.map((promise) =>{ 12 return promise.then(resolveHandler, rejectHandler) 13 }) 14 // 每个 promise 需要用 Promise.resolve 包裹下 15 // 以防传递非 promise 16 );
1 function ajax (name) { 2 return new Promise((resolve, reject) =>{ 3 setTimeout(() => { 4 resolve({name: name, age: ‘27‘}) 5 }, 2000) 6 }) 7 } 8 function query (name) { 9 const cache = query.cache || (query.cache = new Map()) 10 if (cache.has(name)) { 11 console.log(‘走缓存了‘) 12 return Promise.resolve(cache.get(name)) 13 } 14 return ajax(name).then((res) => { 15 cache.set(name, res) 16 console.log(cache) 17 return res 18 }) 19 } 20 query (‘wayke‘).then((res) => { 21 console.log(res) 22 })
原文：https://www.cnblogs.com/zhensg123/p/14802059.html