JavaScript provides several data structures to organize data. One of the most powerful and commonly used structures is the object.

Objects allow us to store related data together in a structured way using key–value pairs.

In this article, we will learn:

• What objects are and why they are needed

• How to create objects

• How to access properties

• How to update properties

• How to add and delete properties

• How to loop through object keys

What Are Objects in JavaScript?

An object is a collection of key-value pairs.

Each value is associated with a key (property name).

Structure

key: value

Example:

let person = {
  name: "John",
  age: 25,
  city: "New York"
};

Here:

Key	Value
name	"John"
age	25
city	"New York"

So the object person stores information about a person.

Why Are Objects Needed?

Objects help us group related information together.

Imagine storing information about a person without objects:

let name = "John";
let age = 25;
let city = "New York";

These variables are not connected.

Using an object makes the relationship clear:

let person = {
  name: "John",
  age: 25,
  city: "New York"
};

Now all information belongs to one entity: the person.

Objects vs Arrays

Both objects and arrays store multiple values, but they work differently.

Feature	Array	Object
Data structure	Ordered list	Key-value pairs
Access method	Index	Property name
Example	arr[0]	obj.name

Array Example

let colors = ["red", "blue", "green"];

console.log(colors[0]); 

Output

red

Object Example

let person = {
  name: "John",
  age: 25
};

console.log(person.name);

Output

John

Creating Objects

Objects are created using curly braces {}.

Example

let person = {
  name: "Alice",
  age: 22,
  city: "London"
};

console.log(person);

Output

{ name: 'Alice', age: 22, city: 'London' }

Each property is written as:

key: value

Accessing Object Properties

There are two ways to access object properties.

1. Dot Notation

This is the most common method.

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

console.log(person.name);

Output

Alice

2. Bracket Notation

Bracket notation is useful when the key is stored in a variable.

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

console.log(person["age"]);

Output

22

Using Variables

let key = "name";

console.log(person[key]);

Output

Alice

Updating Object Properties

You can change a property value using assignment.

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

person.age = 23;

console.log(person);

Output

{ name: 'Alice', age: 23 }

Adding New Properties

New properties can be added simply by assigning a value.

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

person.city = "London";

console.log(person);

Output

{ name: 'Alice', age: 22, city: 'London' }

Deleting Properties

The delete keyword removes a property from an object.

let person = {
  name: "Alice",
  age: 22,
  city: "London"
};

delete person.city;

console.log(person);

Output

{ name: 'Alice', age: 22 }

Looping Through Object Keys

To iterate through object properties, we use the for...in loop.

Example

let person = {
  name: "Alice",
  age: 22,
  city: "London"
};

for (let key in person) {
  console.log(key, person[key]);
}

Output

name Alice
age 22
city London

Explanation:

• key represents the property name

• person[key] gives the value

Mind Map -

Assignment: Student Object

Let's create an object representing a student.

Step 1: Create the Object

let student = {
  name: "Rahul",
  age: 20,
  course: "Computer Science"
};

Step 2: Update a Property

student.age = 21;

Step 3: Print All Keys and Values

for (let key in student) {
  console.log(key + ":", student[key]);
}

Output

name: Rahul
age: 21
course: Computer Science