Understanding Object-Oriented Programming in JavaScript

Introduction

Object-Oriented Programming (OOP) is one of the most widely used programming styles. It helps developers organize code into objects, making programs easier to build, understand, and maintain.

In JavaScript, OOP allows us to create reusable structures using classes and objects.

Let’s explore the core ideas step by step.

What Object-Oriented Programming (OOP) Means

Object-Oriented Programming is a programming approach where we organize code around objects rather than just functions.

An object is a bundle of:

• Properties → data

• Methods → actions/behaviors

Example

const car = {
  brand: "Toyota",
  start() {
    console.log("Car started");
  }
};

Here:

• brand → property

• start() → method

Instead of writing separate variables and functions everywhere, OOP groups related things together inside objects.

Real-World Analogy: Blueprint → Objects

To understand OOP easily, imagine a car factory.

• A blueprint defines how a car should be built.

• From that blueprint, the factory can create many cars.

In programming:

Real World	Programming
Blueprint	Class
Car	Object
Building a car	Creating an instance

So a class is a blueprint, and objects are the actual things created from that blueprint.

What is a Class in JavaScript

A class defines the structure for creating objects.

It describes:

• what properties objects will have

• what methods they can use

Example

class Car {
  brand = "Toyota";

  start() {
    console.log("Car started");
  }
}

Here:

• Car is a class

• It defines a property brand

• It defines a method start()

But this alone doesn't create a car yet.

Creating Objects Using Classes

To create an object from a class, we use the new keyword.

Example

class Car {
  brand = "Toyota";

  start() {
    console.log("Car started");
  }
}

const car1 = new Car();
const car2 = new Car();

car1.start(); // output -> Car started

Here:

• car1 and car2 are objects

• Both are created from the same class

This is why classes are powerful:
One blueprint → many objects.

Constructor Method

A constructor is a special method that runs automatically when an object is created.

It is usually used to initialize properties.

Example

class Car {
  constructor(brand, model) {
    this.brand = brand;
    this.model = model;
  }
}

const car1 = new Car("Toyota", "Camry");
const car2 = new Car("Honda", "Civic");

console.log(car1.brand);
console.log(car2.model);

Here:

• constructor() receives values

• this refers to the current object

So each object can store different data.

Methods Inside a Class

Methods define actions an object can perform.

Example

class Person {
  constructor(name) {
    this.name = name;
  }

  greet() {
    console.log("Hello, my name is " + this.name);
  }
}

const person1 = new Person("Janardan");
person1.greet(); // output -> Hello, my name is Janardan

So:

• name → property

• greet() → method

Objects combine data + behavior.

Basic Idea of Encapsulation

Encapsulation means keeping related data and methods together inside a class.

Instead of writing separate code everywhere

Without Structure

let name = "Jana";

function greet() {
  console.log("Hello " + name);
}

Using encapsulation

class Person {
  constructor(name) {
    this.name = name;
  }

  greet() {
    console.log("Hello " + this.name);
  }
}

// call greet method of person object
const person = new Person("Jana");
person.greet(); // Output: Hello Jana

Now everything related to a Person is inside the class.

Benefits:

• Code becomes organized

• Easier to maintain

• Improves reusability

Assignment

Create a Student class with properties and methods.

Requirements

• Properties: name, age

• Method: print student details

• Create multiple students

Example

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

  printDetails() {
    console.log("Name: " + this.name + ", Age: " + this.age);
  }
}

const student1 = new Student("Rahul", 20);
const student2 = new Student("Karan Ajula", 22);
const student3 = new Student("Anita", 19);

student1.printDetails(); // Name: Rahul, Age: 20
student2.printDetails(); // Name: Karan Ajula, Age: 22
student3.printDetails(); // Name: Anita, Age: 19

There we see an OOP is a organized code using objects, Class acts like a blueprint and Objects are instances created from a class, Constructor initializes object properties and Methods define object behavior.