What Does new Do?

The new keyword creates an object from a constructor function.

It automates object creation and prototype linking.

Constructor Functions

A constructor function is a normal function used to create objects.

By convention, constructor names start with uppercase letters.

Example

function User(name, age) {
  this.name = name;
  this.age = age;
}

Creating an Object With new

const user1 = new User("Ali", 22);

console.log(user1);

Output

User { name: 'Ali', age: 22 }

Constructor → Instance Flow

flowchart LR
    A[User Constructor] --> B[new User()]
    B --> C[user1 instance]

What Happens Internally?

When using new:

1. A new empty object is created

2. this points to that object

3. Properties are added

4. Prototype is linked

5. Object is returned automatically

Step-by-Step Object Creation

Step 1: Empty Object Created

{}

Step 2: this Points to Object

this = {}

Step 3: Properties Added

this.name = name;
this.age = age;

Step 4: Object Returned

Final object:

{
  name: "Ali",
  age: 22
}

Without new

Incorrect:

function User(name) {
  this.name = name;
}

const user = User("Ali");

console.log(user);

Problem

undefined

Because no object was created automatically.

Adding Methods to Constructor

function User(name) {
  this.name = name;

  this.greet = function () {
    console.log(`Hello ${this.name}`);
  };
}

const user1 = new User("Sara");

user1.greet();

Output

Hello Sara

Instances Created From Constructors

Each object created with new is called an instance.

Example

const user1 = new User("Ali");
const user2 = new User("Sara");

Both are instances of User.

Checking Instance Type

Use:

instanceof

Example

console.log(user1 instanceof User);

Output

true

Prototype Linking

Every object created with new is linked to the constructor’s prototype.

Example

function User(name) {
  this.name = name;
}

User.prototype.greet = function () {
  console.log(`Hello ${this.name}`);
};

const user1 = new User("Ali");

user1.greet();

Why Use Prototype?

Methods are shared between instances instead of recreated every time.

Better memory efficiency.

Prototype Linking Visual

Constructor vs Instance

Real-World Analogy

Multiple Instances Example

function Product(name, price) {
  this.name = name;
  this.price = price;
}

const product1 = new Product("Laptop", 50000);
const product2 = new Product("Phone", 25000);

console.log(product1);
console.log(product2);

Output

Product { name: 'Laptop', price: 50000 }
Product { name: 'Phone', price: 25000 }

Common Beginner Mistake

Forgetting new.

Incorrect:

const user = User("Ali");

Correct:

const user = new User("Ali");

Modern Alternative: Classes

Modern JavaScript often uses classes internally built on constructors.

Example

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

const user1 = new User("Ali");

Key Takeaways

Final Notes

The new keyword is a foundational JavaScript concept because it powers:

• Constructor functions

• Classes

• Prototype inheritance

• Object-oriented programming

Even modern class syntax internally uses constructor and prototype behavior.