As programs grow, we often need to store related information together.

For example, imagine storing information about a person:

• Name

• Age

• City

Using separate variables can become messy.

let name = "Gagan";
let age = 22;
let city = "Delhi";

Instead, JavaScript provides objects, which allow us to store related data together in one structure.

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What is an Object?

An object is a collection of key-value pairs.

Each piece of information has:

• a key (property name)

• a value (the data stored)

Example:

let person = {
  name: "Gagan",
  age: 22,
  city: "Delhi"
};

Here:

Key	Value
name	"Gagan"
age	22
city	"Delhi"

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Visual Representation of an Object

4

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Why Objects Are Needed

Objects help us:

• group related information

• represent real-world entities

• organize data clearly

• make programs easier to maintain

Example real-world representation:

let person = {
  name: "Rahul",
  age: 25,
  city: "Mumbai"
};

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Creating Objects

Objects are created using curly braces {}.

Example:

let car = {
  brand: "Toyota",
  model: "Camry",
  year: 2023
};

This object stores information about a car.

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Accessing Object Properties

JavaScript provides two ways to access object properties.

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Dot Notation

This is the most common method.

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

console.log(person.name);
console.log(person.age);

Output

Gagan
22

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Bracket Notation

Properties can also be accessed using brackets.

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

This is useful when property names are dynamic.

Example:

let property = "name";

console.log(person[property]);

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Updating Object Properties

Object values can be updated easily.

Example:

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

person.age = 23;

console.log(person.age);

Output

23

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Adding New Properties

New properties can be added to an object.

Example:

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

person.city = "Delhi";

console.log(person);

Now the object becomes:

{
  name: "Gagan",
  age: 22,
  city: "Delhi"
}

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Deleting Properties

Properties can also be removed.

Example:

delete person.city;

After deletion, the object no longer contains that property.

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Looping Through Object Keys

To iterate through an object's properties, JavaScript provides the for...in loop.

Example:

let person = {
  name: "Gagan",
  age: 22,
  city: "Delhi"
};

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

Output

name Gagan
age 22
city Delhi

Here:

• key represents the property name

• person[key] gives the value

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Array vs Object

Arrays and objects both store data, but they are used differently.

Feature	Array	Object
Structure	Ordered list	Key-value pairs
Access method	Index	Property name
Example	[10,20,30]	{name:"Gagan"}

Example array:

let numbers = [10, 20, 30];

Example object:

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

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Array vs Object Visualization

4

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Practical Example

let person = {
  name: "Gagan",
  age: 22,
  city: "Delhi"
};

console.log(person.name);

Output

Gagan

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Practice Assignment

Create a Student Object

Create an object representing a student.

Properties:

• name

• age

• course

Example:

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

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Update a Property

Update the student's age.

student.age = 21;

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Print All Keys and Values

Use a loop to print all properties.

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

Explain which structure you used and why objects are suitable for representing a student.