Preface - Functional Programming in JavaScript (2015)

Functional Programming in JavaScript (2015)


Functional programming is a style that emphasizes and enables the writing of smarter code, which minimizes complexity and increases modularity. It's a way of writing cleaner code through clever ways of mutating, combining, and using functions. JavaScript provides an excellent medium for this approach. JavaScript, the Internet's scripting language, is actually a functional language at heart. By learning how to expose its true identity as a functional language, we can implement web applications that are powerful, easier to maintain, and more reliable. By doing this, JavaScript's odd quirks and pitfalls will suddenly become clear and the language as a whole will make infinitely more sense. Learning how to use functional programming will make you a better programmer for life.

This book is a guide for both new and experienced JavaScript developers who are interested in learning functional programming. With a focus on the progression of functional programming techniques, styles, and detailed information about JavaScript libraries, this book will help you to write smarter code and become a better programmer.

What this book covers

Chapter 1, The Powers of JavaScript's Functional Side – a Demonstration, sets the pace of the book by creating a small web application with the help of both traditional methods and functional programming. It then compares these two methods to underline the importance of functional programming.

Chapter 2, Fundamentals of Functional Programming, introduces you to the core concepts of functional programming as well as built-in JavaScript functions.

Chapter 3, Setting Up the Functional Programming Environment, explores different JavaScript libraries and how they can be optimized for functional programming.

Chapter 4, Implementing Functional Programming Techniques in JavaScript, explains the functional paradigm in JavaScript. It covers several styles of functional programming and demonstrates how they can be employed in different scenarios.

Chapter 5, Category Theory, explains the concept of Category Theory in detail and then implements it in JavaScript.

Chapter 6, Advanced Topics and Pitfalls in JavaScript, highlights various drawbacks you may face while programming in JavaScript, and the various ways to successfully deal with them.

Chapter 7, Functional and Object-oriented Programming in JavaScript, relates both functional and object-oriented programming to JavaScript, and shows you how the two paradigms can complement each other and coexist side by side.

Appendix A, Common Functions for Functional Programming in JavaScript, contains common functions used to perform functional programming in JavaScript.

Appendix B, Glossary of Terms, includes a glossary of terms used throughout the book.

What you need for this book

Only a browser is needed to get you up and running.

Who this book is for

If you are a JavaScript developer interested in learning functional programming, looking for a quantum leap toward mastering the JavaScript language, or just want to become a better programmer in general, then this book is ideal for you. This guide is aimed at programmers involved in developing reactive frontend applications, server-side applications that wrangle with reliability and concurrency, and everything else in between.


In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

Function.prototype.partialApply = function() {

var func = this;

args =;

return function() {

return func.apply(this, args.concat(




When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

var messages = ['Hi', 'Hello', 'Sup', 'Hey', 'Hola'];,i){

return printSomewhere(s, i*10, i*10);


New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Clicking the Next button moves you to the next screen."


Warnings or important notes appear in a box like this.


Tips and tricks appear like this.