Let's look at a basic example of a promise with two (made-up) asynchronous methods, one to call a web service and another to store the results in a database. JavaScript myWebService.get("http://www.example.com") .then(function(result){returnmyDb.add(result); }) .then(function(){...
}functiongetUsername(person) {returnperson.username; } asyncfunctionchainedFetchMessages(p, username) {//In this function, p is a promise. We wait for it to finish,//then run fetchMessages().const obj =await p; const data=await fetchMessages(username);return{ ...obj, [username]: data};...
}functiongetUsername(person) {returnperson.username; } asyncfunctionchainedFetchMessages(p, username) {//In this function, p is a promise. We wait for it to finish,//then run fetchMessages().const obj =await p; const data=await fetchMessages(username);return{ ...obj, [username]: data};...
1fetch('products.json').then(function(response) {2returnresponse.json();3}).then(function(json) {4products =json;5initialize();6}).catch(function(err) {7console.log('Fetch problem: ' +err.message);8}); 这里fetch()只需要一个参数— 资源的网络 URL — 返回一个promise. promise 是表示异...
Asynchronous JavaScript The examples used in the previous chapter, was very simplified. The purpose of the examples was to demonstrate the syntax of callback functions: Example functionmyDisplayer(something) { document.getElementById("demo").innerHTML= something; ...
Async functions are the next logical step in the evolution of asynchronous programming in JavaScript. They will make your code much cleaner and easier to maintain. Declaring a function asasyncwill ensure that it always returns aPromiseso you don’t have to worry about that anymore. ...
JavaScript:Retry asynchronous readFile()函数 我想用javascript读一个文件。必须先下载此文件,不能立即使用。这意味着,如果使用readFile()访问此文件失败,并在catch块中结束,则应重复此操作。 const fse = require('fs-extra') let retries = 0 function read_a_file(path) {...
Q promises provide a fail shorthand for then when you are only interested in handling the error:var outputPromise = getInputPromise() .fail(function (error) { });If you are writing JavaScript for modern engines only or using CoffeeScript, you may use catch instead of fail....
asyncfunction*readLines(path){letfile=awaitfileOpen(path);try{while(!file.EOF){yieldawaitfile.readLine();}}finally{awaitfile.close();}} This function then returns an async generator object, which can be consumed withfor-await-ofas shown in the previous example. ...
Exceptions are an important feature of the Java language and a basic control flow. In the Java language, a function is allowed to have one return value and throw multiple different types of exceptions. The return value of the function is a normal exit. The function return indicates that the...