是后者,因为当一个Promise resolved 后,它就不能再被rejected。 一旦你调用一种方法(resolve 或reject),另一种方法就会失效,因为 promise 处于稳定状态。让我们探索一个 promise 的所有不同状态。 1.2 Promise 状态 Promise 可以分为四个状态: ⏳ Pending:初始状态,异步操作仍在进行中。 ✅ Fulfilled:操作成功...
const axios = require('axios');// `axios.get()` returns a promise representing an HTTP request.const promise = axios.get('https://httpbin.org/get?answer=42');// The `then()` function lets you register a callback that JavaScript// will call when the HTTP request succeeds.promise.then...
The ES6 promise constructor takes a function. That function takes two parameters,resolve(), andreject(). In the example above, we’re only usingresolve(), so I leftreject()off the parameter list. Then we callsetTimeout()to create the delay, and callresolve()when it’s finished. You ca...
Well, the good news is that any function that returns a promise can be used with async/await. I’m not saying that we should async/await all the things (this syntax does have its downsides, as we’ll see when we get on to error handling), but we should be aware that this is poss...
a function being called. When you see a variable followed by round brackets(…), that’s the signal that a function is being called. Flash forward, every function returns something (either a value, an object orundefined). Whatever is returned from the function will be assigned to variableb...
Sometimes, you might want to convert a JavaScript function that accepts a callback to one that returns aPromiseobject. This lesson shows how to manually wrap a promise-based API around thefs.readFile()function. It also explains how to use theutil.promisify()method that is built into the No...
The async keyword is used to define a function that returns a Promise, and await is used to pause the execution of the function until the Promise is settled. Sandeep PandaView Author Sandeep is the Co-Founder of Hashnode. He loves startups and web technologies. James HibbardView Author ...
Using async/await is another way to work with asynchronous code in a synchronous-looking manner. The async keyword is used to define a function that returns a promise, and await is used to pause the execution until the promise is resolved. Here’s an example: async function fetchData() ...
How to use .finally() as a consumer function? How to use Promise.all() as a consumer function? How to use Promise.race() as a function? What are promises in JavaScript? APromise in JavaScriptis an object that holds the future value of an asynchronous operation.For example, if we are...
Note : fetch is a function that returns a Promise that allows to do an AJAX request Let's see how we could fetch a github user with promises first:function getGithubUser(username) { return fetch(`https://api.github.com/users/${username}`).then(response => response.json()); } get...