What is the new Keyword Used for in JavaScript?

The new keyword in JavaScript is used to create an instance of an object from a constructor function. It initializes a new object and binds this to it, enabling object-oriented programming (OOP) in JavaScript.

How new Works

When you use new with a function, four key things happen:

1. Creates a new empty object ({}).
2. Sets the prototype of this object to the constructor’s prototype.
3. Binds this to the new object inside the constructor.
4. Returns the object (unless the constructor returns a different object).

Example: Constructor Function with new

function Car(make, model) {
  this.make = make;
  this.model = model;
}

const myCar = new Car('Toyota', 'Camry');
console.log(myCar.make); // Output: "Toyota"

Here, new Car() creates an object with make and model properties.

What Happens Without new?

If you forget new, this refers to the global object (or undefined in strict mode), leading to bugs:

const badCar = Car('Honda', 'Civic'); // ❌ No `new`  
console.log(badCar); // undefined  
console.log(window.make); // "Honda" (leaks to global scope!)  

Common Interview Questions

1. What does new do under the hood?
   (Answer: Creates an object, sets prototype, binds this, and returns it.)

2. How is new different from Object.create()?
   (Answer: new calls a constructor, while Object.create() directly sets a prototype.)

3. Can arrow functions be used with new?
   (Answer: No, they lack their own this binding.)

Best Practices

• Always use new with constructor functions.
• Follow PascalCase naming for constructors (e.g., function User()).
• Use ES6 class syntax (which internally uses new).