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)

Pure Functions

Pure functions are a key component of Functional Programming. A pure function can be defined as a function that does not have any effect on or make use of any state outside of the function. A function must meet three key criteria to be considered pure:

  • A function must always return the same output, when given the same inputs.

  • A function must have no side effects.

  • A function must have referential transparency.

Same Output Given Same Input

Given a set of input values, a pure function must always return the same value when provided those input values. This sounds much more complicated than it is. Simply put, the output of a pure function cannot change unless the input values are changed. This means that a function's internal code cannot depend on any program state outside of the function. A pure function cannot use any variable from outside the function to make calculations or code path decisions. An example of this is shown in the following snippet:

const state = { prop1: 5 }...