Promise.all = (promises) => {
let results=[];
return new Promise((resolve,reject)=>{
let i=0;
while(i promises[i].then(res=>{ results.push(res); i++; if(i===promises.length){resolve(results);} }).catch(err=>{ reject(err); //只要有任何Promise出现reject，Promise.newAll就直接reject }); } }) } 如果想捕获promise.all的错误又想返回怎么办 手写Promise.All，并且在这个All中加一个超时时间 1、使用setTimeout方式，在一个promise.all中设置。 2、将setTimeout封装成promise，然后使用promise.race来输出最快的promise 实现Promise.race Promise.race = function(promises){ return new Promise((resolve,reject) => { let i=0; while(i promises[i].then(res=>{ resolve(res); //出现第一个被resolve的直接resolve }).catch(err=>{ reject(err); //出现第一个被reject的直接reject }); i++; } }) } js实现并发多个请求，返回先得到response的，类似Promise.race的实现 要求1：按以下要求输出 human('Jack').eat().sleep(5).go().rest(10); // I am Jack // Eat // 等 5 秒 // Sleep 5s // Go // 等 10 秒 // Rest 10s 要求2：eat/sleep/go/rest可以改变任意顺序human('Jack').sleep(5).eat().rest(10).go(); function human(name){ return new Human(name) } function Human(name）{ this.name=name this.sayHello() this.queue=Promise.resolve() } Human.prototype.sayHello=function(){ console.log(`I am ${this.name}`) } Human.prototype.eat=function(){ this.queue = this.queue.then(()=>{ return new Promise((resolve)=>{ console.log('Eat') resolve()}) }) return this } Human.prototype.sleep=function(time){ this.queue=this.queue.then(()=>{ return new Promise((resolve)=>{ setTimeout(()=>{ console.log(`Sleep ${time}s`) resolve()},time*1000) }) }) return this } Human.prototype.go=function(){ this.queue=this.queue.then(()=>{ return new Promise((resolve)=>{ console.log('Go') resolve() }) }) return this } Human.prototype.rest=function(time){ this.queue=this.queue.then(()=>{ return new Promise((resolve)=>{ setTimeout(()=>{ console.log(`Rest ${time}s`); resolve()},time*1000) }) }) return this } human('Jack').eat().sleep(5).go().rest(10); function cancelableXHR(URL){ var req=newXMLHttpRequest(); var promise=new Promise((resolve,reject)=>{ req.open('GET',URL,true); req.onload=function(){ if(req.status===200){resolve(req.responseText);} else{reject(new Error(req.statusText));} }; req.onerror=function(){reject(new Error(req.statusText));}; req.onabort=function(){reject(new Error('abort this request'));}; req.send(); }); var abort=function(){ if(req.readyState!==XMLHttpRequest.UNSENT){req.abort();} }; return{ promise:promise, abort:abort }; }