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
PacktPub.com
Contributors
Preface
Index

Implementing modules – the old way


Before ES6, JavaScript had never supported modules natively. Developers used other techniques and third-party libraries to implement modules in JavaScript. Using Immediately-Invoked Function Expression (IIFE), Asynchronous Module Definition (AMD), CommonJS, and Universal Module Definition (UMD) are various popular ways of implementing modules in ES5. As these ways were not native to JavaScript, they had several problems. Let's take an overview of each of these old ways of implementing modules.

Immediately-Invoked Function Expression (IIFE)

We've briefly discussed IIFE functions in earlier chapters. It is basically an anonymous function that is executed automatically. Let's take a look at one example. This is how a typical old JS module that uses IIFE looks:

//Module Starts 

(function(window){ 
const sum =(x, y) => x + y;
const sub = (x,y) => x - y;
const math = { 
  findSum(a, b) { return sum(a, b) }, 
  findSub(a,b) { return sub(a, b) }
} 
window.math...