Understanding Object-Oriented Programming in JavaScript

When applications become large, it becomes difficult to manage code if everything is written in simple functions. To organize code better, JavaScript provides a programming style called Object-Oriented Programming (OOP).

OOP helps developers create structured, reusable, and easy-to-maintain code.

1. What Object-Oriented Programming (OOP) Means

Object-Oriented Programming (OOP) is a programming approach where we organize code using objects and classes.

An object contains:

• Properties → data

• Methods → actions or functions

Example:

A car object might have:

• properties → color, brand, speed

• methods → start(), stop(), accelerate()

OOP helps us group data and behavior together.

2. Real-World Analogy: Blueprint → Objects

A simple way to understand OOP is by using a blueprint example.

Think about building cars.

• A blueprint describes how a car should look and behave.

• Many cars can be created from the same blueprint.

In programming:

• The blueprint = class

• The car created from blueprint = object

Example:

Car blueprint:

• brand

• color

• speed

From this blueprint we can create many cars.

Example:

• Car 1 → Toyota, Red

• Car 2 → Honda, Black

• Car 3 → BMW, White

All of them follow the same structure.

3. What Is a Class in JavaScript

A class is like a blueprint used to create objects.

JavaScript introduced the class keyword in ES6.

Example:

class Person {

}

This class currently has no properties or methods, but it defines a structure.

4. Creating Objects Using Classes

Objects are created from classes using the new keyword.

Example:

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

const person1 = new Person("Harshal", 25);
const person2 = new Person("Amit", 30);

Here:

• person1 and person2 are objects

• Both are created from the Person class

5. Constructor Method

The constructor is a special method inside a class.

It runs automatically when an object is created.

It is used to initialize properties.

Example:

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

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

console.log(car1.brand);
console.log(car1.color);

Output:

Toyota
Red

The constructor helps assign values when creating objects.

6. Methods Inside a Class

Classes can also contain methods, which are functions inside the class.

Example:

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

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

const user = new Person("Harshal");

user.greet();

Output:

Hello, my name is Harshal

Here:

• greet() is a method

• It belongs to the Person class

7. Basic Idea of Encapsulation

Encapsulation means keeping related data and functions together inside one object or class.

Example:

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

  showMarks() {
    console.log(this.name + " scored " + this.marks);
  }
}

const student1 = new Student("Amit", 85);

student1.showMarks();

Here:

• name and marks are data

• showMarks() is the method

Both are kept inside the Student class.

This makes the program organized and easier to understand.