Book Image

Advanced JavaScript

By : Zachary Shute
Book Image

Advanced JavaScript

By: Zachary Shute

Overview of this book

If you are looking for a programming language to develop flexible and efficient applications, JavaScript is an obvious choice. Advanced JavaScript is a hands-on guide that takes you through JavaScript and its many features, one step at a time. You'll begin by learning how to use the new JavaScript syntax in ES6, and then work through the many other features that modern JavaScript has to offer. As you progress through the chapters, you’ll use asynchronous programming with callbacks and promises, handle browser events, and perform Document Object Model (DOM) manipulation. You'll also explore various methods of testing JavaScript projects. In the concluding chapters, you'll discover functional programming and learn to use it to build your apps. With this book as your guide, you'll also be able to develop APIs using Node.js and Express, create front-ends using React/Redux, and build mobile apps using React/Expo. By the end of Advanced JavaScript, you will have explored the features and benefits of JavaScript to build small applications.
Table of Contents (9 chapters)


In JavaScript, a promise is an object that wraps an asynchronous operation and notifies the program when the asynchronous operation completes. The promise object represents the eventual completion or failure of the wrapped operation. A promise is a proxy for a value not necessarily known. Instead of providing the value immediately, like a synchronous program, it promises to provide a value at some point in the future. Promises allow you to associate success and error handlers with an asynchronous action. These handlers are called at the completion or failure of the wrapped asynchronous process.

Promises States

Every promise has a state. A promise can only succeed with a value or fail with an error once. The state of a promise defines where the promise is in its work towards the resolution of a value.

A promise comes in three states: pending, fulfilled, or rejected. A promise starts in the pending state. This means that the async operation being done inside the promise is not complete...