Let’s settle the showdown between FP and OOP (or at least laugh while we try).

JavaScript is like that one friend who can adapt to anything—front-end? Back-end? Mobile? Desktop? You name it. But with great flexibility comes great confusion, especially when you’re trying to decide: Should I go functional or object-oriented?

I’ve wrestled with this dilemma myself, sometimes mid-project, sometimes mid-commit. Let’s unpack both styles, compare them in real-life use, and figure out how you can use the best of both worlds without losing your mind (or your codebase).

Why I Fell in Love with Functional Programming (Eventually)

I’ll admit, functional programming used to scare me. Pure functions? Immutability? It all sounded like a strict diet for code. But once I embraced it, I realized how freeing it was.

In FP, your functions are like dependable little machines. Feed them the same input, and they always give you the same output. No weird surprises, no mysterious bugs caused by some rogue global variable. I once spent two hours debugging a weird side effect in an app—turns out, a function had been sneakily mutating state. Pure functions would’ve saved me (and my sanity).

Here’s a simple example:

          const products = [
  { name: 'Laptop', price: 1000 },
  { name: 'Mouse', price: 50 },
  { name: 'Keyboard', price: 150 }
];

const calculateTotalPrice = (items) =>
  items.reduce((total, item) => total + item.price, 0);

console.log(calculateTotalPrice(products)); // 1200
        

That’s clean, testable, and no side effects. FP for the win.

JavaScript’s support for higher-order functions, closures, and array methods like map, filter, and reduce makes it almost feel like it was built for FP. Throw in a library like Immutable.js and you’re in nerd heaven.

Object-Oriented Programming: My First Love

Before I even knew what FP was, I was deep into OOP. I mean, who doesn’t love the idea of modeling real-life things in code? It just makes sense.

You’ve got objects. They have state. They do things. Easy, right?

          class Cart {
  constructor() {
    this.items = [];
  }

  addItem(item) {
    this.items.push(item);
  }

  calculateTotalPrice() {
    return this.items.reduce((total, item) => total + item.price, 0);
  }
}

const cart = new Cart();
cart.addItem({ name: 'Laptop', price: 1000 });
cart.addItem({ name: 'Mouse', price: 50 });
cart.addItem({ name: 'Keyboard', price: 150 });

console.log(cart.calculateTotalPrice()); // 1200
        

Here, the cart knows its state. It manages itself. OOP is fantastic for building things like user interfaces or games, where the behavior and data belong together like peanut butter and jelly.

The Real Difference? It’s All About How You Think About Code

The fight between FP and OOP isn’t about which one is “better.” It’s about your mindset.

FP says: 🧠 “Transform data. Keep it clean. Avoid side effects.”

OOP says: 🧰 “Encapsulate behavior. Let objects manage themselves.”

Let’s compare a real-world task: toggling user authentication.

Functional style:

          const authenticateUser = (isAuthenticated) => !isAuthenticated;

let isAuthenticated = false;
isAuthenticated = authenticateUser(isAuthenticated);
console.log(isAuthenticated); // true
        

OOP style:

          class User {
  constructor() {
    this.isAuthenticated = false;
  }

  authenticate() {
    this.isAuthenticated = true;
  }

  logout() {
    this.isAuthenticated = false;
  }
}

const user = new User();
user.authenticate();
console.log(user.isAuthenticated); // true
        

Which is “better”? Depends on the problem. For a small toggle like this, FP is quick and clean. But if your user object has 10+ behaviors and interacts with multiple systems, OOP shines.

When to Go Functional in JavaScript (Hint: A Lot)

FP is perfect for:

• Data processing (arrays, APIs, logs, etc.)
• Async workflows (Promise, async/await, streams)
• Avoiding side effects and shared state
• Writing reusable utilities or transformations

When I’m building a backend service or processing big data sets, I default to FP. Fewer side effects = fewer bugs. Plus, testing pure functions is a dream. One input, one output, done.

And no, you don’t need to go full FP evangelist. Start by making functions pure and minimizing state. You'll already be ahead of the game.

Where OOP Still Rules in JavaScript

OOP isn’t dead. In fact, if you’ve used React class components (yes, before hooks), or built a game, or worked with large enterprise codebases, you’ve likely leaned on OOP a lot.

OOP is your best friend when:

• Modeling complex systems (like user accounts, carts, vehicles, etc.)
• Maintaining shared internal state
• Creating reusable objects with varying behaviors via inheritance or composition

It’s also easier for some teams to understand, especially when onboarding junior devs. OOP feels intuitive. “This is an object. It does stuff.”

So... Is JavaScript Functional or Object-Oriented? (Spoiler: It’s Both, Kinda)

If you’ve ever argued about whether JavaScript is truly object-oriented or secretly functional at heart, you’re not alone—I’ve been there, pacing around a coffee shop trying to explain prototypal inheritance to a friend who just wanted to build a to-do app.

The truth is, JavaScript is a multi-paradigm language, which is a fancy way of saying, “You can do both, and nobody can stop you.” It has strong object-oriented capabilities, like constructors, prototypes, and even ES6 classes (which are just syntactic sugar over prototypes), but at the same time, it treats functions as first-class citizens—meaning you can pass them around like hot potatoes. This dual nature makes JavaScript incredibly flexible but also a bit chaotic.

One day you’re chaining map() and reduce() like a functional guru, and the next, you're defining class hierarchies like you're writing a Java novel. And honestly? That’s part of the fun. It’s like the JavaScript wizards couldn’t decide, so they said, “Why not both?” —kind of like tacos and pizza. Deliciously confusing.

Final Thoughts: Use What Solves the Problem (and Feels Right)

If you’re still asking, “Which one should I use?”—my honest answer is: both. Mix them. Blend them. Abuse the flexibility of JavaScript.

In one of my client projects, I started with a purely OOP structure. Midway, I introduced functional utilities to clean up logic. It made the codebase easier to test, reason about, and maintain. The result? A hybrid approach that worked great.

So yeah, don't feel like you have to pick a side. Be pragmatic.

JavaScript is versatile enough to let you write beautiful FP or solid OOP—or both in harmony. Just don’t write spaghetti. That’s the only paradigm we should all avoid.