Objects in JavaScript

An object in JavaScript is used to store multiple related values in a single variable. Objects store data in the form of key-value pairs.

For example, a student has related information such as name, age, and course. Instead of creating separate variables, we can store all this information inside one object.

let student = {
    name: "John",
    age: 20,
    course: "JavaScript"
};

console.log(student);

Output:

{
    name: "John",
    age: 20,
    course: "JavaScript"
}

Here, student is an object. name, age, and course are called keys, and "John", 20, and "JavaScript" are called values.

Creating an Object

An object is created using curly braces {}. Each property consists of a key and a value separated by a colon :.

let product = {
    name: "Laptop",
    price: 50000,
    inStock: true
};

In this object:

name, price, and inStock are keys.
"Laptop", 50000, and true are values.

Each key-value pair is separated by a comma.

Accessing Object Properties

We can access object properties in two ways:

Dot Notation
Bracket Notation

1. Dot Notation

Dot notation is the most common way to access an object property.

let product = {
    name: "Laptop",
    price: 50000
};

console.log(product.name);
console.log(product.price);

Output:

Laptop
50000

Here, product.name accesses the value of the name property.

2. Bracket Notation

Bracket notation uses square brackets [] to access object properties.

let product = {
    name: "Laptop",
    price: 50000
};

console.log(product["name"]);
console.log(product["price"]);

Output:

Laptop
50000

The property name is written as a String inside the square brackets.

Dot Notation vs Bracket Notation

Dot Notation	Bracket Notation
Uses a dot `.`	Uses square brackets `[]`
Example: `product.name`	Example: `product["name"]`
Simple and commonly used	Useful when the property name is dynamic
Cannot directly use a variable as a property name	Can use a variable as a property name

For example, bracket notation is useful when the property name is stored in a variable.

let product = {
    name: "Laptop",
    price: 50000
};

let key = "name";

console.log(product[key]);

Output:

Laptop

Here, the value of key is "name", so product[key] accesses the name property.

Adding a New Property

We can add a new property to an existing object.

let user = {
    name: "John"
};

user.age = 25;

console.log(user);

Output:

{
    name: "John",
    age: 25
}

Here, the age property is added to the user object.

Updating an Object Property

We can update the value of an existing property by assigning a new value.

let user = {
    name: "John",
    city: "Chennai"
};

user.city = "Coimbatore";

console.log(user);

Output:

{
    name: "John",
    city: "Coimbatore"
}

Here, the value of city is changed from "Chennai" to "Coimbatore".

Deleting an Object Property

The delete operator is used to remove a property from an object.

let user = {
    name: "John",
    age: 25,
    city: "Chennai"
};

delete user.age;

console.log(user);

Output:

{
    name: "John",
    city: "Chennai"
}

Here, the age property is removed from the object.

Object with Different Data Types

An object can store values of different data types.

let employee = {
    name: "David",
    age: 28,
    isWorking: true,
    skills: ["HTML", "CSS", "JavaScript"]
};

console.log(employee);

Here, the object contains a String, Number, Boolean, and Array.

Objects Can Contain Functions

An object can also contain a function. A function inside an object is called a method.

let person = {
    name: "John",

    greet: function() {
        console.log("Hello");
    }
};

person.greet();

Output:

Hello

Here, greet is a method of the person object.