📓 4.1.0.2 Introduction to Functional Programming

Up to this point, we have mostly focused on object-oriented programming. We've built objects that store information and have methods attached to them. Object-oriented programming relies on techniques like inheritance and encapsulation.

Functional programming is a completely different paradigm. In general, the goal of a functional program is to be stateless, which means we can no longer store information in objects. Functional programming focuses on what objects do, not on what they are. Instead of storing information in objects, we will pass information between functions. We will no longer mutate state — that means we won't even reassign values to variables. In other words, no more let, only const.

Object-oriented programming focuses on objects themselves while functional programming is focused on functions. We've used OOP in very concrete ways; for instance, a dog barks or a player stores a score.

In functional programming, our goal is to make our functions more abstract. This can make functional programming harder to grasp at first. However, once a function is abstracted, we can use it with many different objects. While OOP uses inheritance to give many kinds of objects functionality, functional programming uses a technique called composition. We will learn more about composition and how it works in a future lesson.

While we will focus on functional programming techniques during this course section, both object-oriented and functional programming have their advantages and disadvantages. A good coder will incorporate both paradigms, even in the same application.