Objects in JavaScript

In many programs, we need to represent real-world entities such as a person, a student, a product, or a car. These entities often have multiple related properties.

JavaScript provides objects to organize this type of data in a clear and structured way.

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What Are Objects and Why Do We Need Them?

An object is a data structure that stores information as key-value pairs.

Each piece of data has:

• a key (also called a property name)
• a value (the data stored in that property)

Example:

let person = {
  name: "Alice",
  age: 25,
  city: "London"
};

Here:

Key	Value
name	"Alice"
age	25
city	"London"

Objects help us:

• Represent real-world data
• Organize related information together
• Access and update data easily

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Array vs Object

It is helpful to understand the difference between arrays and objects.

Array

Arrays store ordered values and are accessed using indexes.

let fruits = ["Apple", "Banana", "Mango"];

console.log(fruits[0]); // Apple

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Object

Objects store named values and are accessed using keys.

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

console.log(person.name); // Alice

Summary:

Feature	Array	Object
Structure	Ordered list	Key-value pairs
Access	Index (0,1,2)	Key name
Use case	Lists of values	Structured data

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Creating Objects

Objects are created using curly braces {}.

Example:

let person = {
  name: "John",
  age: 30,
  city: "New York"
};

Each property is written as:

key: value

Multiple properties are separated by commas.

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Accessing Properties

There are two ways to access object properties:

• Dot notation
• Bracket notation

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Dot Notation

This is the most common way.

let person = {
  name: "John",
  age: 30
};

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

Output:

John
30

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Bracket Notation

Properties can also be accessed using brackets.

let person = {
  name: "John",
  age: 30
};

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

Output:

John
30

Bracket notation is useful when the property name is stored in a variable.

Example:

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

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Updating Object Properties

You can update the value of an existing property.

Example:

let person = {
  name: "John",
  age: 30
};

person.age = 31;

console.log(person);

Output:

{ name: "John", age: 31 }

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Adding New Properties

New properties can be added easily.

Example:

let person = {
  name: "John",
  age: 30
};

person.city = "Paris";

console.log(person);

Output:

{ name: "John", age: 30, city: "Paris" }

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Deleting Properties

Properties can be removed using the delete keyword.

Example:

let person = {
  name: "John",
  age: 30,
  city: "Paris"
};

delete person.city;

console.log(person);

Output:

{ name: "John", age: 30 }

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Looping Through Object Keys

To go through all properties of an object, we can use a for...in loop.

Example:

let person = {
  name: "Alice",
  age: 25,
  city: "London"
};

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

Output:

name Alice
age 25
city London

Explanation:

• key represents each property name
• person[key] retrieves its value

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Assignment

Questions

1. Create an object representing a student.

2. Add properties such as:

• name
• age
• course

1. Update one property.

2. Print all keys and values using a loop.

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Answers

1. Create a Student Object

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

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2. Update One Property

student.age = 21;

console.log(student);

Output:

{ name: "Rahul", age: 21, 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 21
course Computer Science

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Conclusion

Objects are an essential part of JavaScript because they allow us to represent structured data using key-value pairs. They are commonly used to represent real-world entities such as users, products, or students.

By learning how to create objects, access properties, update values, and loop through keys, you build a strong foundation for working with more complex data in JavaScript applications.