Constructor Method

A constructor method is a special method used inside a class to initialize object properties when a new object is created.

A constructor runs automatically when an object is created from a class.

Why Do We Need a Constructor?

Constructors help to:

Initialize object data

Assign default values

Set up an object when it is created

Without a constructor, objects would have no initial state.

Constructor Syntax (ES6 Class)

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

Creating an Object Using Constructor

const person1 = new Person("Rahul", 25);
const person2 = new Person("Anjali", 22);

console.log(person1.name, person1.age);
console.log(person2.name, person2.age);

Output

Rahul 25
Anjali 22

Constructor executes automatically
this refers to the current object

Key Point

A class can have only one constructor
Constructor name must be constructor
It executes automatically when new keyword is used
Constructor cannot be called manually

Constructor Without Parameters

class Car {
    constructor() {
        this.brand = "Toyota";
    }
}

const car1 = new Car();
console.log(car1.brand);

Constructor with Default Values

class User {
    constructor(name = "Guest") {
        this.name = name;
    }
}

const user1 = new User();
const user2 = new User("Nikhil");

console.log(user1.name); // Guest
console.log(user2.name); // Nikhil

Constructor in Inheritance (super( ))

When using inheritance, the child class must call super().

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

class Dog extends Animal {
    constructor(name, breed) {
        super(name);
        this.breed = breed;
    }
}

const dog1 = new Dog("Buddy", "Labrador");
console.log(dog1.name, dog1.breed);

super() calls parent constructor
Mandatory before using this

When to Use Constructor

When creating multiple objects with similar structure

When initializing object properties

When working with classes and inheritance

Two Minute Drill

Constructor initializes object properties
It runs automatically with new
Only one constructor per calss
this refers to the current object
super( ) is required in child classes
Constructor does not return values

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Constructor Method

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