When we write programs, we often need to store many details about one thing.

Example: A person.

A person can have:

• name

• age

• city

• job

We could store these in separate variables, but that becomes messy.

Example:

let name = "Ravi";
let age = 25;
let city = "Hyderabad";

Instead, JavaScript gives us a better way to group related information.

That is called an Object.

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1. What is an Object?

An object is a collection of key-value pairs.

Think of it like an ID card.

Name → Ravi
Age → 25
City → Hyderabad

In JavaScript:

let person = {
  name: "Ravi",
  age: 25,
  city: "Hyderabad"
};

Here:

• name, age, city → keys

• "Ravi", 25, "Hyderabad" → values

So an object stores information about something in an organized way.

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2. Creating an Object

We create objects using curly braces {}.

Example:

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

This object contains three properties.

You can print the entire object:

console.log(person);

Output:

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

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3. Accessing Object Properties

We can access values in two ways:

1️⃣ Dot Notation
2️⃣ Bracket Notation

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Dot Notation

Example:

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

console.log(person.name);

Output:

Arjun

Here we accessed the name property.

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Bracket Notation

Example:

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

Output:

22

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

Example:

let key = "city";

console.log(person[key]);

Output:

Delhi

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4. Updating Object Properties

We can change values inside an object.

Example:

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

person.age = 23;

console.log(person.age);

Output:

23

The value changed from 22 → 23.

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5. Adding New Properties

We can also add new properties to an object.

Example:

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

person.city = "Hyderabad";

console.log(person);

Output:

{ name: "Arjun", age: 22, city: "Hyderabad" }

A new property city was added.

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6. Deleting Properties

We can remove properties using the delete keyword.

Example:

let person = {
  name: "Arjun",
  age: 22,
  city: "Hyderabad"
};

delete person.city;

console.log(person);

Output:

{ name: "Arjun", age: 22 }

The city property was removed.

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7. Looping Through Object Keys

Sometimes we want to print all properties of an object.

We can use a for...in loop.

Example:

let person = {
  name: "Arjun",
  age: 22,
  city: "Hyderabad"
};

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

Output:

name Arjun
age 22
city Hyderabad

Here:

• key → property name

• person[key] → value

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Object vs Array (Important Difference)

Arrays and objects both store data, but they work differently.

Array

Array stores values using index numbers.

Example:

let fruits = ["apple", "banana", "mango"];

Access using index:

fruits[0]

---

Object

Object stores values using keys.

Example:

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

Access using key:

person.name

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Simple Comparison

Feature	Array	Object
Data Access	Index	Key
Structure	Ordered list	Key-value pairs
Example	fruits	person details

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Visual Representation of an Object

person
│
├── name → Ravi
├── age → 25
└── city → Hyderabad

Each key is connected to a value.

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Assignment Practice

Try this in your browser console.

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1. Create a Student Object

let student = {
  name: "Rahul",
  age: 21,
  course: "Computer Science"
};

---

2. Update One Property

student.age = 22;

console.log(student);

Output:

{ name: "Rahul", age: 22, course: "Computer Science" }

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3. Print All Keys and Values

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

Output:

name Rahul
age 22
course Computer Science