oop in javascript

Mastering OOP Principles in JavaScript

Module - 8 OOPS in JavaScript
Mastering OOP Principles in JavaScript


Object-Oriented Programming (OOP) was introduced in programming to provide a better way of organizing and managing code. Before OOP, programming was typically done using procedural programming languages, which focused on defining a series of steps to accomplish a specific task. This approach worked well for simple tasks, but as programs became more complex, the code became more difficult to understand, maintain, and reuse.

OOP is a programming paradigm that organizes code into objects that have properties and methods. This approach is more natural and intuitive because it mirrors the way we think about the world. OOP allows developers to break down complex programs into smaller, more manageable pieces, making it easier to understand and maintain the code.

Object-Oriented Programming (OOP) is a popular programming paradigm that focuses on creating objects with properties and methods that can interact with each other. OOP principles such as inheritance, encapsulation, and polymorphism are essential in building robust and efficient programs. JavaScript is a versatile language that supports OOP principles, and this lesson will explore how to master inheritance, encapsulation, and polymorphism in JavaScript.


Inheritance is a core concept of Object-Oriented Programming (OOP) that allows a class to inherit properties and methods from another class, called the superclass or parent class. The class that inherits from the superclass is called the subclass or child class.

Inheritance enables us to create new classes based on existing classes, without having to rewrite the code for the common properties and behaviors. The subclass can add new properties and methods, or override the existing ones, to provide its own implementation.

Inheritance provides several benefits, including:

Inheritance is a principle that allows objects to inherit properties and methods from a parent object. JavaScript supports prototype-based inheritance, where objects inherit properties and methods from their prototype. The prototype is an object that is shared among all instances of a class.


class Animal {
  constructor(name, age) { = name;
    this.age = age;

  makeSound() {
    console.log("Animal sound");

class Dog extends Animal {
  constructor(name, age, breed) {
    super(name, age);
    this.breed = breed;

  makeSound() {

let myDog = new Dog("Buddy", 5, "Golden Retriever");
console.log(; // Output: Buddy
console.log(myDog.age); // Output: 5
console.log(myDog.breed); // Output: Golden Retriever
myDog.makeSound(); // Output: Woof

In this example, the Dog class extends the Animal class, which means that it inherits the name and age properties and the makeSound method from the Animal class. The Dog class also has its own property, breed, and overrides the makeSound method with its own implementation.


Encapsulation refers to the practice of bundling data and methods that operate on that data within a single unit called a class. Encapsulation enables us to protect data from accidental manipulation and unauthorized access from outside of the class by making the data and methods that operate on that data private or protected.

In encapsulation, the data and methods are defined in such a way that they are accessed only through the methods of the class, and not directly. This allows the class to have control over the data and how it is accessed, ensuring that it is used in the correct way.

Encapsulation is a principle that involves hiding the implementation details of an object and exposing only the necessary interfaces. In JavaScript, encapsulation can be achieved using closures, modules, and classes.


class Person {
  constructor(name, age) {
    let _name = name;
    let _age = age;

    this.getName = function() {
      return _name;

    this.getAge = function() {
      return _age;

    this.setName = function(name) {
      _name = name;

    this.setAge = function(age) {
      _age = age;

let john = new Person("John", 30);
console.log(john.getName()); // Output: John
console.log(john.getAge()); // Output: 30
console.log(john.getName()); // Output: James
console.log(john.getAge()); // Output: 35

In this example, the Person class uses closures to encapsulate the _name and _age properties and provides getter and setter methods to access and modify them. The implementation details of the object are hidden from the outside world, and only the necessary interfaces are exposed.


Polymorphism is another core concept of Object-Oriented Programming that allows objects of different classes to be treated as if they are of the same class. In other words, it is the ability of an object to take on multiple forms.

Polymorphism enables us to write code that can work with objects of different classes, without having to know the specific class of each object. This makes the code more flexible and reusable, and it promotes modularity and extensibility.

Polymorphism is a principle that allows objects of different types to be treated as if they were the same type. In JavaScript, polymorphism can be achieved using function overloading, duck typing, and interface implementation.


function area(shape) {
  if (shape instanceof Rectangle) {
    return shape.width * shape.height;
  } else if (shape instanceof Circle) {
    return Math.PI * Math.pow(shape.radius, 2);
  } else {
    throw new Error("Unsupported shape type");

class Rectangle {
constructor(width, height) {
this.width = width;
this.height = height;

class Circle {
constructor(radius) {
this.radius = radius;

let rectangle = new Rectangle(5, 10);
let circle = new Circle(5);

console.log(area(rectangle)); // Output: 50
console.log(area(circle)); // Output: 78.53981633974483

In this example, the area function takes a shape parameter and calculates its area based on its type. If the shape is a Rectangle object, it calculates the area using the width and height properties. If the shape is a Circle object, it calculates the area using the radius property. This allows objects of different types to be treated as if they were the same type, which is an example of polymorphism.


Inheritance, encapsulation, and polymorphism are essential OOP principles that can help developers create efficient and maintainable programs. JavaScript supports these principles through prototype-based inheritance, closures, modules, classes, function overloading, duck typing, and interface implementation. By mastering these principles, developers can create powerful and flexible programs that are easy to maintain and extend.

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