Book Image

Learn ECMAScript - Second Edition

By : MEHUL MOHAN, Narayan Prusty
Book Image

Learn ECMAScript - Second Edition

By: MEHUL MOHAN, Narayan Prusty

Overview of this book

Learn ECMAScript explores implementation of the latest ECMAScript features to add to your developer toolbox, helping you to progress to an advanced level. Learn to add 1 to a variable andsafely access shared memory data within multiple threads to avoid race conditions. You’ll start the book by building on your existing knowledge of JavaScript, covering performing arithmetic operations, using arrow functions and dealing with closures. Next, you will grasp the most commonly used ECMAScript skills such as reflection, proxies, and classes. Furthermore, you’ll learn modularizing the JS code base, implementing JS on the web and how the modern HTML5 + JS APIs provide power to developers on the web. Finally, you will learn the deeper parts of the language, which include making JavaScript multithreaded with dedicated and shared web workers, memory management, shared memory, and atomics. It doesn’t end here; this book is 100% compatible with ES.Next. By the end of this book, you'll have fully mastered all the features of ECMAScript!
Table of Contents (18 chapters)
Title Page

Promises and async programming

JavaScript now has a new native pattern for writing asynchronous code called the Promise pattern. This new pattern removes the common code issues that the event and callback pattern had. It also makes the code look more like synchronous code. A promise (or a Promise object) represents an asynchronous operation. Existing asynchronous JavaScript APIs are usually wrapped with promises, and the new JavaScript APIs are purely implemented using promises. Promises are new in JavaScript but are already present in many other programming languages. Programming languages, such as C# 5, C++ 11, Swift, Scala, and more are some examples that support promises. Let's see how to use promises.

Promise states

A promise is always in one of these states:

  • Fulfilled: If the resolve callback is invoked with a non-promise object as the argument or no argument, then we say that the promise is fulfilled
  • Rejected: If the rejecting callback is invoked or an exception occurs in the executor...