What Is a Constructor?

A Constructor is one of the most important parts of a Class in Object-Oriented Programming.

In most cases, a class contains a constructor because it is responsible for performing the object’s initial setup (initialization) when a new object is created.

Common responsibilities include:

• Receiving the initial data needed to create an object.
• Initializing the object’s attributes.
• Running code that should execute once when the object is created.

Creating a Constructor

To define a constructor inside a class, use the constructor keyword followed by parentheses () and a method body.

// Model
class Car {
  constructor() {
    console.log("This is a car model");
  }
}

// Object
const car = new Car();

What Happens Here?

We created a class named Car and added a constructor to it.

Then we created an object using:

const car = new Car();

As soon as the object is created, JavaScript automatically calls the constructor, which prints:

This is a car model

Notice that we never called constructor() ourselves—it is executed automatically.

Why Do We Use Parentheses?

The constructor is written as:

constructor() {}

instead of:

constructor {}

because a constructor is a special method, and like every method in JavaScript, it uses parentheses () even when it doesn’t receive any arguments.

Key Takeaways

• A Constructor is a special method inside a class.
• It runs automatically whenever a new object is created.
• Constructors are commonly used to initialize objects and receive initial data.
• A constructor is always written as constructor() because it is a method.