Understanding Object-Oriented Programming in JavaScript

As programs grow bigger, managing code becomes harder.
To organize code better, JavaScript supports Object-Oriented Programming (OOP).

OOP helps us structure code using objects and classes, making programs easier to reuse and maintain.

In this guide we will learn:

• What OOP means

• Real-world analogy (blueprint → objects)

• What a class is

• Creating objects from classes

• Constructor method

• Methods inside a class

• Basic idea of encapsulation

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1. What is Object-Oriented Programming (OOP)?

Object-Oriented Programming is a way of writing code using objects that represent real-world things.

Examples:

Real World	Program
Car	Car object
Student	Student object
Bank Account	Account object

Each object contains:

Properties → information
Methods → actions

Example:

Student
Name → Pankaj
Age → 22

Action → study()

---

Real-Life Analogy (Blueprint → Objects)

Imagine a car blueprint.

The blueprint defines:

• engine

• color

• speed

But the blueprint itself is not a car.

When we build cars from that blueprint, we get objects.

Blueprint → Car Class

Car 1 → Red Car
Car 2 → Blue Car
Car 3 → Black Car

In programming:

Class → blueprint
Object → real instance

---

Blueprint → Object Diagram

       Car Class
        ↓
  ----------------
  | color        |
  | speed        |
  | start()      |
  ----------------
      ↓    ↓    ↓
   Car1  Car2  Car3

---

2. What is a Class in JavaScript?

A class is a blueprint used to create objects.

Example syntax:

class ClassName {
  constructor() {
  }

  methodName() {
  }
}

---

3. Creating a Class

Example: Person

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

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

Explanation:

Part	Meaning
class Person	blueprint
constructor	initializes values
greet()	method

---

4. Creating Objects from a Class

To create objects we use the new keyword.

Example:

let person1 = new Person("Pankaj", 25);
let person2 = new Person("Rahul", 22);

Now we have two objects.

---

Calling a Method

person1.greet();
person2.greet();

Output

Hello my name is Pankaj
Hello my name is Rahul

---

Class → Instance Relationship

Class: Person
   ↓
new Person()

   ↓
Object Created

person1
person2
person3

---

5. Constructor Method

The constructor is a special method that runs automatically when a new object is created.

Example:

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

Creating objects:

let car1 = new Car("BMW", 200);
let car2 = new Car("Audi", 220);

Now:

car1.brand → BMW
car2.brand → Audi

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6. Methods Inside a Class

Methods are functions defined inside a class.

Example:

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

  drive() {
    console.log(this.brand + " is driving");
  }
}

Usage:

let car = new Car("BMW", 200);

car.drive();

Output

BMW is driving

---

7. Encapsulation

Encapsulation means keeping data and behavior together inside a class.

Example:

Car object

Properties
brand
speed

Methods
drive()
stop()

Instead of managing these separately, they stay organized inside the class.

Benefits:

• cleaner code

• reusable structure

• easier maintenance

---

Example (Student Class)

class Student {

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

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

}

Create objects:

let student1 = new Student("Pankaj", 22);
let student2 = new Student("Rahul", 21);

Use the method:

student1.showDetails();
student2.showDetails();

Output

Name: Pankaj
Age: 22

Name: Rahul
Age: 21

---

Create a Class

Create a class called Student.

Properties:

• name

• age

---

Add a Method

Add a method that prints student details.

Example idea:

printDetails(){
  console.log(this.name + " is " + this.age + " years old");
}

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Create Multiple Objects

Example:

let s1 = new Student("Amit", 20);
let s2 = new Student("Riya", 21);
let s3 = new Student("Rahul", 22);

---

Call the Method

s1.printDetails();
s2.printDetails();
s3.printDetails();

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Final Thought:

Object-Oriented Programming helps you build large and scalable applications.

You will use OOP heavily in:

• JavaScript applications

• Node.js backend

• React applications

• game development

• real-world software systems

Mastering classes and objects is a big step toward becoming a strong JavaScript developer.