Understanding Objects in JavaScript

What Are Objects and Why Are They Needed?

Imagine a real person.

A person has: name, age and city

If we store these separately:

let name = "Rahul";
let age = 22;
let city = "Bangalore";

These variables are not connected.

But in real life, these details belong to one person.

So we group them together using an object.

What is Object?

Object = Key - Value Pair Structure

An object stores data in key - value pairs.

Think of it like:

Key      → Value
name     → Rahul
age      → 22
city     → Bangalore

In JavaScript:

let person = {
  name: "Rahul",
  age: 22,
  city: "Bangalore"
};

Here:

• person → object name

• name, age, city → keys

• "Rahul", 22, "Bangalore" → values

How to create an object?

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

This is the simplest and most used way.

Accessing Object Properties

There are two ways to access values.

• Dot Notation

• Bracket Notation

Dot Notation

console.log(person.name);    // Rahul
console.log(person.age);     // 22

Bracket Notation

console.log(person["city"]);    // Bangalore

Bracket notation is useful when:

• Property name is dynamic

• Property name has spaces

Example:

let key = "name";
console.log(person[key]);    // Rahul

Updating Object Properties

You can change values of any key in the objects easily.

person.age = 25;
console.log(person.age);    // 25

Objects are mutable (values can change).

Adding and Deleting Properties

Adding New Property

person.country = "India";
console.log(person);

Now object becomes:

{
    name: "Rahul",
    age: 25,
    city: "Bangalore",
    country: "India"
}

Deleting Property

delete person.city;
console.log(person);

Now city is removed.

Looping Through Object Keys

To print all properties, use for...in loop.

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

Output:

name : Rahul
age : 25
country : India

How it works:

• key stores property name

• person[key] gives the value

Difference Between Array and Object

Array	Object
Stores ordered list	Stores key-value pairs
Uses index (0,1,2...)	Uses named keys
Example: ["Rahul", 22]	Example: {name: "Rahul", age: 22}

Assignment

1. Create an object representing a student

2. Add properties like name, age, course

3. Update one property

4. Print all keys and values using a loop

// Create an object representing a student with name, age and course
let student = {
  name: "Visshnnu Tejaa",
  age: 27,
  course: "Web dev Cohort"
}

// Update age property
student.age = 28

// Print all keys and values using a loop
for (let key in student){
  console.log(key, student[key])
}

Output:

"name", "Visshnnu Tejaa"
"age", 28
"course", "Web dev Cohort"