Object-Oriented Programming in JavaScript: A Complete Guide

Object Oriented Programming (OOP) is a style of programming that uses classes and object to represent real world entity , object and that's property(data) and behaviors(methods) .

Instead of write scattered variable and function , OOP group them into object .

Traditional Approach (❌ Messy):

let personName = "John";
let personAge = 25;
let personCity = "Mumbai";

function printPerson() {
    console.log(personName + " is " + personAge + " years old");
}

OOP Approach (✅ Organized):

class Person {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
    
    printDetails() {
        console.log(this.name + " is " + this.age + " years old");
    }
}

const person1 = new Person("John", 25);
person1.printDetails();

🔧 Real-World Analogy: Blueprint → Objects

Imagine a car manufacture compnay:

A car Blueprint that :

• Contains design, specifications

• Used to manufacture many cars

• Follows by each car

• But each car is unique (different color, number)

Code :

class Car {
    constructor(color, engineSize) {
        this.color = color;
        this.engineSize = engineSize;
    }
    
    honk() {
        console.log("Beep beep!");
    }
}

const car1 = new Car("Red", "2L"); // Car 1
const car2 = new Car("Blue", "2L"); // Car 2
const car3 = new Car("White", "3L"); // Car 3

console.log(car1.color); // Output: Red
console.log(car2.color); // Output: Blue
car1.honk(); // Output: Beep beep!

Key Concept

• Class = Blueprint (template)

• Object = Actual thing created from blueprint

• Many objects can use the same class

What is Class

A class is a blueprint or template fir creating object .

Class Syntax:

class ClassName {
    constructor(parameters) {
        // Initialize properties
    }
    
    method() {
        // Do something
    }
}

Key Components

1. Class name - Always starts with capital letter (Person, Car, Student)

2. Constructor - Special method that runs when creating object

3. Properties - Variables inside class (name, age, color)

4. Methods - Functions inside class (greet, honk, study)

Creating Objects Using Classes

Create a class :

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

Create object from the class :

const car1 = new Car("Toyota", "Red");
const car2 = new Car("Honda", "Blue");
const car3 = new Car("BMW", "Black");

Access properties

console.log(car1.brand); // Output: Toyota
console.log(car2.color); // Output: Blue
console.log(car3.brand); // Output: BMW

⚠️ Important Notes

• Class name must be capitalized (Person, not person)

• Use new keyword to create objects

• Constructor runs automatically when creating object

• Each object is independent (changing one doesn't affect others)

What is Constructor?

A constructor is a special method that runs automatically when you create a new object.

Purpose:

• Initialize properties

• Set up default values

• Prepare the object

Constructor Syntax

class ClassName {
    constructor(param1, param2) {
        this.property1 = param1;
        this.property2 = param2;
    }
}

What are Methods?

Methods are functions inside a class that can access and modify object properties.

Syntax:

class ClassName {
    method1() {
        // Code here
    }
    
    method2() {
        // Code here
    }
}

Encapsulation

Encapsulation is a concept in OOP that refer to how to hide the internal details of an object and exposing only necessary information to the outside world !

Real Life Example :

1. Coca-Cola 🥤

The formula for Coca‑Cola soft drink is one of the most famous secrets in the world.

• Only a few people know the exact recipe.

• The formula is kept in a vault in World of Coca‑Cola.

• Factories only receive ingredients in prepared form, not the full recipe.

So:

1. Example: Burger 🍔

Companies like Burger King and McDonald's also keep:

• special sauce recipes

• spice mixes

• cooking processes

secret from the public.

Customers only see the final burger, not how the recipe is made.

How to relate in programming

class Car {
    constructor(brand) {
        this.brand = brand;
        this.fuel = 100;
    }
    
    drive() {
        if (this.fuel > 0) {
            this.fuel = this.fuel - 10;
            console.log("Driving...");
        } else {
            console.log("No fuel!");
        }
    }
    
    
    checkFuel() {
        console.log("Fuel: " + this.fuel);
    }
}

const car = new Car("Toyota");
car.drive();
car.checkFuel();

User doesn't need to know how fuel works, just:

- Call drive()

- Call checkFuel()

May be this blog help you !

Happy Coding