Understanding Constructor Functions in JavaScript

#javascript #beginners #basic

In JavaScript, a constructor function is used to create multiple objects with similar properties and methods. Instead of creating objects manually again and again, we use a constructor to generate them easily.

What is an Object?

An object stores data in key–value pairs.

Example:

let person = {
  name: "Harini",
  age: 22
};

Here:

name and age are keys
"Harini" and 23 are values If we want to create many similar objects, writing this structure repeatedly is not efficient. That’s why we use constructor functions.

What is a Constructor Function?

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

By convention, constructor function names should start with a capital letter.
Example:

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

Here:

this refers to the newly created object.
this.name assigns a property to that object.

Creating an Object Using new
To create an object from a constructor, we use the new keyword.

let user1 = new User();
console.log(user1);

What happens when we use new?

When we write new User():

A new empty object is created.
this refers to that new object.
Properties are added to the object.
The object is returned automatically.

We do not need to manually write return this.

Creating Multiple Objects

Each time we use new, a new object is created.

let user1 = new User();
let user2 = new User();

Both user1 and user2 are separate objects.

Constructor with Arguments

Constructor functions can also accept parameters.

Example:

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

let user1 = new User("Harini");
console.log(user1);

Now the value is passed dynamically instead of being hardcoded.
This makes the constructor more flexible.

Adding Properties and Methods
We can add both properties and methods inside a constructor.
Example:

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

let user1 = new User("Harini", 22);
console.log(user1.getAge());