2. What is a promise A promiseis an object that encapsulates the result of an asynchronous operation. Each promise has state, which can have one of the following values: Pending Fullfilledwith avalue Rejectedfor areason The just created promise is in apendingstate. The promise maintains thepen...
Promise接受一个函数作为参数,这个参数函数的两个参数分别是resolved和rejected,用来执行了两种状态的回调函数。 当Promise实例生成后,用then方法来指定两种状态的回调函数。举一个简单例子 //axios是一个基于Promise的http请求,可以直接调用then this.axios.get(url).then((res)=>{ //请求成功 resolved的回调 },(er...
JavaScript is an object-based scripting language. Syntax: JavaScript syntax is not as formal or structured as Java. Thus, it’s simpler for most users. Compilation: Java is a compiled language, whereas JavaScript is an interpreted language that is interpreted line by line at run-time; compiled...
1. Client-Side Scripting: JavaScript is primarily used for client-side scripting, meaning it runs in the web browser of the user, as opposed to server-side languages like PHP or Python. This enables it to manipulate the Document Object Model (DOM) of a web page, making it possible to up...
A callback function in JavaScript is a function that is passed as an argument to another function and is invoked after some kind of event.
What is a Promise()? What will this function return? What value will this expression return? String interpolation is a much-needed new feature that is finally available in JavaScript. See the example below. Is there anything wrong with it? Rest is a new way for functions to handle ...
What does "object destructuring" mean and what is the result of a destructuring operation?Say you have an object with some properties:const person = { firstName: 'Tom', lastName: 'Cruise', actor: true, age: 57 }You can extract just some of the object properties and put them into ...
What is a Promise()? What will this function return? What value will this expression return? String interpolation is a much-needed new feature that is finally available in JavaScript. See the example below. Is there anything wrong with it? Rest is a new way for functions to handle ...
The Promise.reject() method produces a Promise object that is intentionally rejected with a specified reason. If a JavaScript Promise doesn't have a rejection handler and gets rejected, the unhandledrejection event is emitted to the script's global scope, usually the window object or a Worker,...
JavaScript Copy In this example, as more operations are added, the indentation levels grow, making the code harder to follow and maintain. Promises in JavaScript A Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value. It is a ...