Introduction

In the previous chapter, we talked about how JavaScript is a multi-paradigm programming language. It's possible to write code with procedural, object-oriented, and functional design patterns. In this chapter, we'll look closely at the functional programming design pattern.

Functional programming is a programming paradigm that has become popular in the last few years, though most JavaScript developers were unfamiliar with it before then.

JavaScript is not a purely functional language like some others, such as Haskell, Scheme, and Clojure. However, JavaScript has support for functional structures and techniques if you choose to use them. It is worthwhile becoming familiar with its concepts and gaining a working knowledge of how to use them.

Functional programming has a set of features. Among others, here are some of the important ones:

• Pure functions
• Immutability and avoiding shared state, mutable data, and side effects
• Declarative rather...