Understanding Object-Oriented Programming in JavaScript

What is Object-Oriented Programming (OOP)?

Object-Oriented Programming (OOP) is a programming approach where we organize code around objects instead of just functions and logic.

In OOP, we group data (properties) and behavior (methods) together into a single unit called an object.

This makes code:

• Easier to understand

• Reusable

• Organized

• Scalable

Blueprint → Objects

Think about a car blueprint:

• A blueprint defines structure (color, engine, wheels).

• But the blueprint itself is not a real car.

• Using the blueprint, we can create many real cars.

In OOP:

Real World	Programming
Blueprint	Class
Real Car	Object

So, a class is a template, and an object is a real instance created from it.

What is a Class in JavaScript?

A class in JavaScript is a template used to create objects with shared properties and methods.

Example:

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

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

Here:

• Person → class

• name, age → properties

• greet() → method

Creating Objects Using Classes

We create objects using the new keyword:

const person1 = new Person("Arnab", 22);
const person2 = new Person("Riya", 20);

person1.greet(); // Hello, my name is Arnab
person2.greet(); // Hello, my name is Riya

Notice how we reuse the same class to create multiple objects.

Constructor Method (Special Function)

The constructor runs automatically when an object is created.

It is used to:

• Initialize values

• Set up properties

Example:

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

const car1 = new Car("Toyota", "Red");

Methods Inside a Class

Methods are functions defined inside a class.

Example:

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

  study() {
    console.log(this.name + " is studying.");
  }
}

const s1 = new Student("Rahul");
s1.study();

Basic Idea of Encapsulation

Encapsulation means:

Keeping data and methods together
Controlling how data is accessed

Simple example:

class BankAccount {
  constructor(balance) {
    this.balance = balance;
  }

  deposit(amount) {
    this.balance += amount;
  }
}

Users don’t directly change balance. Instead, they use methods like deposit().

This keeps data safe and organized.

Why OOP is Useful (Code Reusability)

Instead of writing the same code again:

• Write once inside a class

• Create multiple objects

Saves time and reduces errors.

Small Example Set (Beginner Friendly)

Example 1: Person

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

  speak() {
    console.log(this.name + " is speaking.");
  }
}

Example 2: Car

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

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

Assignment Idea (Practice)

Create a class called Student

Requirements:

1. Add properties:

   • name

   • age

2. Add method:

   • Print student details

3. Create multiple student objects

Example Solution:

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

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

const s1 = new Student("Arnab", 21);
const s2 = new Student("Riya", 20);

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