JavaScript Objects

Arrays are useful for storing a list of values. But what if we want to store information about one thing, such as a student, car, or mobile phone? This is where JavaScript Objects are useful. An object stores related information together using key-value pairs.

JavaScript Objects

What is an Object?

An object is a collection of related data and actions. For example, a student can have a name, age, and course.

let student = {
    name: "Rahul",
    age: 14,
    course: "JavaScript"
};

console.log(student);

Output:

{name: "Rahul", age: 14, course: "JavaScript"}

Here:

• name, age, and course are called properties.
• "Rahul", 14, and "JavaScript" are their values.

Creating an Object

We create an object using curly brackets {}.

let car = {
    brand: "Toyota",
    model: "Camry",
    year: 2025
};

Each property is written as:

key: value

Accessing Object Properties

We can access an object’s property using the dot . operator.

let student = {
    name: "Aman",
    age: 14
};

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

Output:

Aman
14

We can also use square brackets:

console.log(student["name"]);

Output:

Aman

Changing Object Properties

Object properties can be changed after creating the object.

let student = {
    name: "Aman",
    age: 14
};

student.age = 15;

console.log(student.age);

Output:

15

Adding and Deleting Properties

We can add a new property using the dot operator.

let student = {
    name: "Aman",
    age: 14
};

student.city = "Delhi";

console.log(student.city);

Output:

Delhi

We can delete a property using the delete keyword.

delete student.age;

console.log(student);

Nested Objects

An object can contain another object. This is called a nested object.

let student = {
    name: "Aman",
    address: {
        city: "Delhi",
        country: "India"
    }
};

console.log(student.address.city);

Output:

Delhi

JavaScript Methods and this

What is an Object Method?

A method is a function stored inside an object.

let student = {
    name: "Aman",

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

student.greet();

Output:

Hello!

Here, greet is an object method.

The this Keyword

The this keyword refers to the current object. It is commonly used inside object methods.

let student = {
    name: "Aman",

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

student.greet();

Output:

Hello Aman

Here, this.name means the name property of the current student object.

JavaScript Constructor

What is a Constructor Function?

A constructor function helps us create multiple objects with the same structure. We use the new keyword to create objects from a constructor.

function Student(name, age) {
    this.name = name;
    this.age = age;
}

let student1 = new Student("Aman", 14);
let student2 = new Student("Riya", 15);

console.log(student1.name);
console.log(student2.name);

Output:

Aman
Riya

The constructor lets us create many student objects without writing the same structure again and again.

JavaScript Getter and Setter

Getters and setters are used to read and change object properties in a controlled way.

Getter

A getter uses the get keyword to return a value.

let student = {
    firstName: "Aman",
    lastName: "Kumar",

    get fullName() {
        return this.firstName + " " + this.lastName;
    }
};

console.log(student.fullName);

Output:

Aman Kumar

Notice that we use student.fullName like a property, not like a function.

Setter

A setter uses the set keyword to change a value.

let student = {
    name: "Aman",

    set studentName(newName) {
        this.name = newName;
    }
};

student.studentName = "Riya";

console.log(student.name);

Output:

Riya

The setter runs when we assign a new value.

JavaScript Prototype

What is a Prototype?

Every JavaScript object has a prototype. A prototype allows objects to share properties and methods. For example, we can add a method to a constructor’s prototype.

function Student(name) {
    this.name = name;
}

Student.prototype.greet = function() {
    console.log("Hello " + this.name);
};

let student1 = new Student("Aman");
let student2 = new Student("Riya");

student1.greet();
student2.greet();

Output:

Hello Aman
Hello Riya

The greet() method is added to the prototype, so objects created from Student can use it.

Why use Prototypes?

Prototypes are useful when we want many objects to share the same method instead of creating a separate copy of that method for every object.

Quick Recap

• An object stores related information using key-value pairs.
• Object properties store data.
• Object methods are functions inside objects.
• this refers to the current object.
• A constructor function helps create multiple similar objects.
• Getters read values and setters change values.
• A prototype allows objects to share properties and methods.

Frequently Asked Questions (FAQs)

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Nidhi Srivastav