As programs grow, managing data and behavior becomes harder.
Object-Oriented Programming (OOP) helps organize code by grouping data and related functions together.

In JavaScript, OOP is often implemented using classes and objects.

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What Object-Oriented Programming Means

Object-Oriented Programming is a way of writing code where:

• Data is stored in objects

• Behavior is defined through methods

• Objects are created from classes

In simple terms:

OOP models software based on real-world entities.

Examples:

Real World	Programming
Car	Car object
Student	Student object
Bank account	Account object

Each object contains:

• Properties → data

• Methods → actions

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Real-World Analogy: Blueprint → Objects

Imagine a car blueprint used in a factory.

The blueprint describes:

• color

• model

• engine

• start() method

From one blueprint, many cars can be produced.

Programming works the same way.

Blueprint (Class)
      ↓
Creates
      ↓
Objects (Instances)

Example:

Car Class → Car1, Car2, Car3

Each car object has the same structure but different values.

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What Is a Class in JavaScript

A class is a template for creating objects.

It defines:

• properties

• methods

Basic syntax:

class Person {

}

A class itself does nothing until objects are created from it.

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Creating Objects Using Classes

Objects are created using the new keyword.

Example:

class Person {}

const person1 = new Person();

Here:

• Person → class

• person1 → object

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Constructor Method

The constructor runs automatically when an object is created.

It is used to initialize properties.

Example:

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

Now create objects:

const person1 = new Person("Rahul", 22);
const person2 = new Person("Amit", 25);

Result:

person1 → {name: "Rahul", age: 22}
person2 → {name: "Amit", age: 25}

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Methods Inside a Class

Methods define actions objects can perform.

Example:

class Person {

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

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

Create object:

const person1 = new Person("Rahul", 22);

person1.greet();

Output:

Hello my name is Rahul

Here:

• greet() is a method

• this.name refers to the object's property

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Example: Car Class

class Car {

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

  start() {
    console.log(this.brand + " car started");
  }

}

Create objects:

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

car1.start();
car2.start();

Output

Toyota car started
Honda car started

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Basic Idea of Encapsulation

Encapsulation means keeping data and behavior together in one unit (class).

Example:

Student
 ├── name
 ├── age
 └── printDetails()

Instead of writing scattered code, everything is organized in one place.

Benefits:

• cleaner code

• easier maintenance

• better structure

Encapsulation is a core concept in Object-Oriented Programming.

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Blueprint → Object Diagram

            CLASS (Blueprint)
                Car
        ┌───────────────────┐
        │ brand             │
        │ model             │
        │ start()           │
        └───────────────────┘
                 │
         Creates objects
                 │
        ┌────────┴────────┐
        │                 │
     Car1              Car2
   Toyota Camry      Honda Civic

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Class → Instance Relationship

Class
Person
  │
  ├── person1 → Rahul
  ├── person2 → Amit
  └── person3 → Neha

One class can generate many objects.

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Why OOP Is Useful

OOP helps with:

• code reusability

• better organization

• easier debugging

• scalable applications

Modern frameworks built with JavaScript—like Node.js and React—often use OOP concepts internally.

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Assignment

1. Create a Student Class

Create a class:

class Student {

}

Add properties:

• name

• age

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2. Add a Method

Create a method:

printDetails()

Example output:

Name: Rahul
Age: 21

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3. Create Multiple Objects

Example:

const student1 = new Student("Rahul", 21);
const student2 = new Student("Amit", 22);

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4. Call the Method

student1.printDetails()
student2.printDetails()

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Key Takeaway

Object-Oriented Programming organizes code using:

• Classes → blueprint

• Objects → real instances

• Properties → data

• Methods → actions

Understanding these basics is essential before moving into deeper topics like:

• inheritance

• polymorphism

• abstraction