How to Extend an Object in JavaScript ?

Last Updated : 25 Jun, 2024

Extending an object in JavaScript means adding properties or methods to enhance its functionality. This can be done dynamically. The extends keyword is used to create a subclass from a parent class, enhancing object-oriented programming flexibility in JavaScript.

Syntax:

class childclass extends parentclass {...}
class parentclass extends in-built object {...}

The following example shows how a child class inherits properties from a parent class using the extends keyword. The Profile class has two attributes, name and age. The `Student` class extends Profile, adds attribute languages, and displays all attributes.

Example: In this example, we use the extends keyword.

JavaScript

// Declaring class 
class Profile {

    // Constructor of profile class 
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }

    getName() {

        // Method to return name 
        return this.name;
    }

    getAge() {

        // Method to return age 
        return this.age;
    }

    getClass() {
        return this;
    }
}

// Class Student extends class Profile 
class Student extends Profile {

    // Each data of class Profile can be 
    // accessed from student class. 
    constructor(name, age, languages) {

        // Acquiring of attributes of parent class 
        super(name, age);
        this.lang = [...languages];
    }

    // Method to display all attributes 
    getDetails() {
        console.log("Name : " + this.name);
        console.log("Age : " + this.age);
        console.log("Languages : " + this.lang);
    }
}

// Creating object of child class with passing of values 
let student1 = new Student("Ankit Dholakia", 24,
    ['Java', 'Python', 'PHP', 'JavaScript']);
student1.getDetails();

Output

Name : Ankit Dholakia
Age : 24
Languages : Java,Python,PHP,JavaScript

Example: In this example, we will see how spread syntax can be used to extend two objects into a third object and display the containing attributes of both objects.