Object-Oriented Programming (OOP) is a powerful paradigm that has revolutionized the way we structure and organize code.

While JavaScript began as a prototype-based language, it has evolved to embrace OOP principles, particularly with the introduction of ES6 and subsequent updates.

This post delves into the core concepts of OOP in JavaScript, exploring how they can be implemented to create more robust, maintainable, and scalable applications.

We'll journey through the four pillars of OOP - Inheritance, Abstraction, Encapsulation and Polymorphism - demonstrating how each principle can be applied in JavaScript. Along the way, we'll examine real-world examples and discuss the pros and cons of each concept.

Whether you're a seasoned developer looking to refine your OOP skills in JavaScript or a newcomer eager to grasp these fundamental concepts, this guide will provide valuable insights into harnessing the power of OOP in your JavaScript projects.

1. Inheritance:

Inheritance allows a class to inherit properties and methods from another class. It promotes code reusability and establishes a relationship between a parent class and a child class.

class Vehicle {
  constructor(make, model) {
    this.make = make;
    this.model = model;
  }

  getInfo() {
    return `${this.make} ${this.model}`;
  }

  start() {
    return "The vehicle is starting...";
  }
}

class Car extends Vehicle {
  constructor(make, model, doors) {
    super(make, model);
    this.doors = doors;
  }

  getCarInfo() {
    return `${this.getInfo()} with ${this.doors} doors`;
  }
}

const myCar = new Car("Toyota", "Corolla", 4);
console.log(myCar.getCarInfo()); // Output: Toyota Corolla with 4 doors
console.log(myCar.start()); // Output: The vehicle is starting...

In this example, Car inherits from Vehicle, gaining access to its properties and methods.

Pros:

• Code reusability: Child classes inherit properties and methods from parent classes.

• Establishes a clear hierarchy between objects.

• Allows for method overriding and extension.

Cons:

• Can lead to tight coupling between parent and child classes.

• Deep inheritance hierarchies can become complex and hard to maintain.

2. Abstraction

Abstraction involves hiding complex implementation details and showing only the necessary features of an object. In JavaScript, we can achieve abstraction using abstract classes (though not natively supported) and interfaces.

class Shape {
  constructor() {
    if (new.target === Shape) {
      throw new TypeError("Cannot instantiate abstract class");
    }
  }

  calculateArea() {
    throw new Error("Method 'calculateArea()' must be implemented.");
  }
}

class Circle extends Shape {
  constructor(radius) {
    super();
    this.radius = radius;
  }

  calculateArea() {
    return Math.PI * this.radius ** 2;
  }
}

class Rectangle extends Shape {
  constructor(width, height) {
    super();
    this.width = width;
    this.height = height;
  }

  calculateArea() {
    return this.width * this.height;
  }
}

// const shape = new Shape(); // Throws TypeError
const circle = new Circle(5);
const rectangle = new Rectangle(4, 6);

console.log(circle.calculateArea()); // Output: 78.53981633974483
console.log(rectangle.calculateArea()); // Output: 24

In this example, Shape acts as an abstract class that can't be instantiated directly. It defines a common interface calculateArea that all subclasses must implement. This abstraction allows us to work with different shapes through a common interface without worrying about their specific implementations.

Pros:

• Simplifies complex systems by hiding unnecessary details.

• Improves code maintainability and reduces duplication.

• Allows focusing on what an object does rather than how it does it.

Cons:

• Can lead to over-simplification if not designed carefully.

• Might introduce performance overhead in some cases.

3. Encapsulation

Encapsulation is the bundling of data and the methods that operate on that data within a single unit (object). In JavaScript, we can use closures and symbols to create private properties and methods.

class BankAccount {
  #balance = 0;  // Private field

  constructor(owner) {
    this.owner = owner;
  }

  deposit(amount) {
    if (amount > 0) {
      this.#balance += amount;
      return true;
    }
    return false;
  }

  withdraw(amount) {
    if (amount > 0 && this.#balance >= amount) {
      this.#balance -= amount;
      return true;
    }
    return false;
  }

  getBalance() {
    return this.#balance;
  }
}

const account = new BankAccount('John Doe');
account.deposit(1000);
console.log(account.getBalance()); // Output: 1000
console.log(account.#balance); // SyntaxError: Private field '#balance' must be declared in an enclosing class

In this example, #balance is a private field that can't be accessed directly from outside the class.

Pros:

• Data protection: Prevents unauthorized access to internal data.

• Modularity: Bundles related functionality together.

• Easier maintenance: Changes to internal implementation don't affect external code.

Cons:

• Can be complex to implement in JavaScript due to lack of true private members.

• Might lead to verbose code when creating getters and setters.

4. Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common superclass. In JavaScript, this can be achieved through method overriding.

class Animal {
  speak() {
    return "The animal makes a sound";
  }
}

class Dog extends Animal {
  speak() {
    return "The dog barks";
  }
}

class Cat extends Animal {
  speak() {
    return "The cat meows";
  }
}

const animals = [new Animal(), new Dog(), new Cat()];

animals.forEach(animal => {
  console.log(animal.speak());
});

// Output:
// The animal makes a sound
// The dog barks
// The cat meows

In this example, each class implements the speak method differently, demonstrating polymorphism.

Pros:

• Flexibility: Objects of different types can be treated uniformly.

• Extensibility: New classes can be added without changing existing code.

• Simplifies code by allowing use of a single interface for different types.

Cons:

• Can make code harder to debug if overused.

• Might lead to performance overhead in some languages (less so in JavaScript).

As we've explored, Object-Oriented Programming in JavaScript offers a robust toolkit for creating structured, maintainable, and scalable code. The four pillars of OOP - Inheritance, Abstraction, Encapsulation and Polymorphism - each bring unique strengths to the table, allowing developers to model complex systems, protect data integrity, promote code reuse, and create flexible, extensible applications.

While implementing these principles in JavaScript may sometimes require creative approaches due to the language's unique characteristics, the benefits are clear. OOP can lead to more organized codebases, easier collaboration among team members, and increased adaptability to changing requirements.

However, it's important to remember that OOP is not a one-size-fits-all solution. Each project may require a different balance of these principles, and in some cases, other paradigms might be more suitable. The key is to understand these concepts thoroughly and apply them judiciously, always keeping in mind the specific needs of your project and team.

Happy Coding 😄