For example, when you request data from the server by using a promise, it will be in a pending state. When the data arrives successfully, it will be in a fulfilled state. If an error occurs, then it will be in a rejected state. Create a Promise To create a promise object, we use ...
//for this example, you will see following output// then function in thenobject// Promise object resolve function is called Then function is calledvar thenobject = { then: function(resolve, reject){ console.log("then function in thenobject"); resolve("Then function is called"...
Example using Promise letmyPromise =newPromise(function(myResolve, myReject) { letreq =newXMLHttpRequest(); req.open('GET',"mycar.html"); req.onload=function() { if(req.status==200) { myResolve(req.response); }else{ myReject("File not Found"); ...
newPromise(function(resolve, reject) { setTimeout(()=> resolve(1),1000); }).then(function(result) { alert(result);//1returnnewPromise((resolve, reject) => {//(*)setTimeout(() => resolve(result *2),1000); }); }).then(function(result) {//(**)alert(result);//2returnnewPromi...
varSpecPromise= Q.when($.get("http://example.com/json")); 另一个例子是使用承诺多填充库(www.promisejs.org/polyfills/promise-4.0.0.js),如下代码所示: varspecPromise =Promise.resolve($.ajax(' http://example.com/json);); 尽管这些承诺实现遵循标准化的行为,但它们的整体 API 存在差异。
根据需求创建多个带有.then()方法的Promise链。在下面的示例中,我们模拟了一个简单的异步操作链,以演示Promise的串行执行特性: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 // 异步操作1functionasyncOperation1(){returnnewPromise((resolve,reject)=>{setTimeout(()=>{console.log("异步操作1完成");res...
Promise 是异步编程的一种解决方案,比传统的解决方案–回调函数和事件更加高效,它开始是在node社区提出和实现,后面ES6将其写进了语言标准,统一了语法,原生...
目前有些 API 直接是基于 Promise 的形式,例如 Fetch API 从网络获取数据。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 fetch('http://example.com/movies.json').then(function(response){// TODO}); 举一个 Node.js 的示例,例如 fs.readFile() 这个 API 默认是 callback 的形式,如果要转为 ...
(//http request promise成功时候的处理//在http request promise成功的时候,开始处理写文件操作function(dataReceived){returnnewPromise(function(resolve,reject){fs.writeFile("temp.txt",dataReceived,function(e){if(e)reject(e);elseresolve("Write file succ");});})}).then(//writeFile promise成功时候...
2. 理解Promise 我们通过一个简单例子先来感受一下Promise。 var p = new Promise(function (resolve, reject) { // ... if(/* 异步操作成功 */){ resolve(ret); } else { reject(error); } }); p.then(function (value) { // 完成态 ...