如果上一个then()中的返回值不是Promise对象,则将该返回值直接传递给下一个then() 如果上一个then()中的返回值是Promise对象,则将Promise对象中resolve返回值传给下一个then() //定义3个函数,分别返回promise对象functionfn1(n){returnnewPromise(resolve =>{ setTimeout( ()=> resolve(n + 1),1000) })...
functionimgLoad(url){// Create new promise with the Promise() constructor;// This has as its argument a function// with two parameters, resolve and rejectreturnnewPromise(function(resolve,reject){// Standard XHR to load an imagevarrequest=newXMLHttpRequest();request.open('GET',url);request....
1000);});promise1.then(result1=>{console.log(result1);// 输出: "Result from Promise 1"varpromise2=newPromise((resolve,reject)=>{setTimeout(()=>{resolve('ResultfromPromise2');},500);});// 返回第二个Promise实例给下一个.then()returnpromise2;}).then(result2=>{console.log...
_this.status='pending';// 每层Promise的待定状态,只有当前Promise处于pending的时候,才会执行异步函数_this.params=null;// 传递的参数_this.tempResolveList=newArray()// 储存链式调用then中的函数队列functionresolve(params) {// 异步操作之后才会执行该方法,执行前一直等待if(params &&typeofparams ==='funct...
functiongetUserName(name){if(!name)thrownewError('用户名无效');returnname;}getUserName() Promise 的异常处理,Promise执行中,本身自带try...catch的异常处理,出错时,将错误Rejact函数。 代码语言:javascript 复制 newPromise((resolve,reject)=>{thrownewError('error!');}).catch(alert); ...
// Create a basic promise functionfunctionpromiseFunction(){returnnewPromise((resolve, reject) =>{// do somethingif(error) {// indicate successreject(error); }else{// indicate errorresolve(data); } }); }// Call a basic promise functionpromiseFunction() ...
2、Promise Promise作为典型的微任务之一,它的出现可以使JS达到异步执行的效果。 一个Promise函数的结构如下列代码如下: const promise = new Promise((resolve, reject) => { resolve('a'); }); promise .then((arg) => { console.log(`执行resolve,参数是${arg}`) }) ...
原生Promise使用方法: constpromise1=newPromise((resolve,reject)=>{setTimeout(()=>{resolve('foo');},300);});promise1.then((value)=>{console.log(value);// expected output: "foo"}); 手写实现: // 状态定义constPENDING='pending'constFULFILLED='fulfilled'constREJECTED='rejected'// Promise 解...
let promise = new Promise(resolve => { setTimeout(() => resolve(2), 2000); }); promise.then(val => console.log(val)); console.log('finished'); We create a promise which resolves after two seconds with an integer value. Thethenfunction attaches callbacks for the resolution and/or ...
Create the promiseWe firstly are going to create a promise. We will use the jQuery get method to do our Ajax request to X.const xFetcherPromise = new Promise( // Create promise using "new" keyword and store it into a variable function(resolve, reject) { // Promise constructor takes a...