Higher Order Functions

A higher order function is a function that takes a function as an argument or returns a function.

Let's look at some common examples.

Callbacks

Callback functions are arguments passed to a function that are then called when some action or event occurs.

This is an extremely common pattern in JavaScript environments like the browser, node, and React Native.

Some functions accept several callback functions for handling different actions.

Functional programming

Programming in a "functional" style, by composing stateless, side-effect free functions, is very common in JavaScript.

We've already seen many standard library examples, like map and reduce. Here's an example of how we might write map.

Higher order functions like map are often implemented using the stateful aspects of JavaScript, e.g. loops.