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JavaScript Classes - GeeksforGeeks

Last Updated : 29 Jul, 2025

JavaScript classes (introduced in ES6) provide a structured way to create objects with shared properties and methods. They support inheritance, encapsulation, and modularity, making it easier to write object-oriented code.

Syntax

class ClassName {
    constructor() {
        // Initialize properties here
    }
    // Define methods here
    methodName() {
        // Method code
    }
}

• The class keyword is used to declare a class.
• The constructor() method is a special method that is automatically called when an instance of the class is created.
• You can define methods inside the class to provide behaviour for objects created from the class.

• Encapsulation: Bundles data (properties) and behaviour (methods) together.
• Constructor Method: Initializes properties when an object is created.
• Inheritance: Allows one class to inherit properties and methods from another.
• Code Reusability: Enables the creation of multiple instances with shared functionality.
• Simplicity & Clarity: Provides a clear structure for creating and managing objects.

A basic class that defines properties and methods. This example shows how to create an object with a constructor and method.

class Person {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
    g() {
        console.log(`Hello, my name is ${this.name} and I am ${this.age} years old.`);
    }
}
let p1 = new Person("Pranjal", 20);
p1.g();

Hello, my name is Pranjal and I am 20 years old.

• The Person class has a constructor to set name and age, and a g method to log a greeting message.
• An instance (p1) is created with new, passing "Pranjal" and 20, then calls g to print the greeting.

The constructor is used to initialize the properties of the object when an instance is created.

class Car {
    constructor(make, model, year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }
    d() {
        console.log(`${this.year} ${this.make} ${this.model}`);
    }
}
let my = new Car("Toyota", "Corolla", 2021);
my.d();

2021 Toyota Corolla

• The Car class has a constructor to initialize make, model, and year, and a d method to log the car's details.
• An instance (my) is created with new, passing "Toyota", "Corolla", and 2021, then calls d to print the car's information.

Inheritance allows one class to extend another, inheriting its properties and methods while adding or overriding functionality.

class Car {
    constructor(make, model, year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }
    di() {
        console.log(`${this.year} ${this.make} ${this.model}`);
    }
}
class ElectricCar extends Car {
    constructor(make, model, year, batteryLife) {
        super(make, model, year);
        this.batteryLife = batteryLife;
    }
    d() {
        console.log(`Battery life: ${this.batteryLife} hours`);
    }
}
let tesla = new ElectricCar("Tesla", "Model S", 2022, 24);
tesla.di()
tesla.d();

2022 Tesla Model S
Battery life: 24 hours

• ElectricCar inherits from Car, using super to set properties and adds batteryLife and d method.
• An instance (tesla) calls both di to display car details and d to show battery life.

Using classes to create multiple objects with the same structure but different data.

class Car {
    constructor(make, model, year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }
    d() {
        console.log(`${this.year} ${this.make} ${this.model}`);
    }
}
let c1 = new Car("Toyota", "Corolla", 2021);
let c2 = new Car("Honda", "Civic", 2020);
c1.d();
c2.d(); 

2021 Toyota Corolla
2020 Honda Civic

• The Car class initializes car details and has a d method to display them.
• Two Car instances (c1 and c2) are created, and d is called on both to show their details.

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