JavaScript is a Functional Language

JavaScript is functional. Yes, you heard that right. People love to argue about this, but the facts are clear. Let’s settle this once and for all: JavaScript is a functional programming language.

Why is JavaScript a functional programming language?

JavaScript checks all the boxes for functional programming. Here’s why:

1. First-Class Functions Functions in JavaScript are treated like first-class citizens. You can pass them around as arguments, return them from other functions, or assign them to variables. They’re just like any other value.

2. Lambda Expressions and Closures JavaScript embraces lambda functions. Combine that with closures, and you are in functional territory.

Closures let functions remember their lexical scope, even when called outside their original context.

For example:

3. Higher-Order Functions You’ve probably used map, reduce, or filter. These are higher-order functions baked into JavaScript. They’re essential for functional programming.

Example:

4. Tail Call Optimization Introduced in ECMAScript 6, tail call optimization is all about efficient recursion. It’s not supported everywhere, but it’s part of the spec.

Here’s what it looks like:

Functional Programming in Action

Let’s dive deeper. JavaScript supports core functional techniques and concepts.

Closures and Modules Before modern modules, closures simulated private state. They’re still useful today.

Currying Currying breaks a function into a series of one-argument functions.

Function Composition Compose multiple functions into one.

Functors and Monads JavaScript can even handle concepts like monads. Sure, it’s not Haskell, but it works.

Example of Maybe monad:

The Verdict

JavaScript is a functional programming language.

It’s not perfect. But it supports the key concepts: first-class functions, closures, higher-order functions, and more.

You can write beautifully functional code in JavaScript if you embrace its features.

Is JavaScript functional? Yes. Case closed.