Book Image

Professional JavaScript

By : Hugo Di Francesco, Siyuan Gao, Vinicius Isola, Philip Kirkbride
Book Image

Professional JavaScript

By: Hugo Di Francesco, Siyuan Gao, Vinicius Isola, Philip Kirkbride

Overview of this book

In depth knowledge of JavaScript makes it easier to learn a variety of other frameworks, including React, Angular, and related tools and libraries. This book is designed to help you cover the core JavaScript concepts you need to build modern applications. You'll start by learning how to represent an HTML document in the Document Object Model (DOM). Then, you'll combine your knowledge of the DOM and Node.js to create a web scraper for practical situations. As you read through further lessons, you'll create a Node.js-based RESTful API using the Express library for Node.js. You'll also understand how modular designs can be used for better reusability and collaboration with multiple developers on a single project. Later lessons will guide you through building unit tests, which ensure that the core functionality of your program is not affected over time. The book will also demonstrate how constructors, async/await, and events can load your applications quickly and efficiently. Finally, you'll gain useful insights into functional programming concepts such as immutability, pure functions, and higher-order functions. By the end of this book, you'll have the skills you need to tackle any real-world JavaScript development problem using a modern JavaScript approach, both for the client and server sides.
Table of Contents (12 chapters)

Pure Functions

Pure functions are functions that don't have side effects and for the same input, arguments will return the same output value(s). A side effect can be anything from mutating the value of an argument passed by reference (which in JavaScript mutates the original) to mutating the value of a local variable, or doing any sort of I/O.

A pure function can be thought of as a mathematical function. It only operates using input and only affects its own output.

Here is a simple pure function, the identity function, which returns whatever is passed to it as a parameter:

const identity = i => i;

Notice how there are no side effects and no mutation of parameters or creation of new variables. This function doesn't even have a body.

Pure functions have the advantage of being simple to reason about. They're also easy to test; there is usually no need to mock any dependencies out since any and all dependencies should be passed as arguments. Pure functions...