Javascript Object

Introduction

In JavaScript, an object is a complex data structure that allows you to store collections of key-value pairs. Objects are one of the core components of JavaScript and are used to represent real-world entities, such as a user, a car, or any other item that has properties and behaviors.

OR

An object is used to store multiple values. An object has a key and a value pair.

What is a JavaScript Object?

A JavaScript Object is a collection of key-value pairs where

1. A key is called a property name.
2. A value can be any data type, such as a string, number, boolean, array, function, or even another object.

Object Syntax

The basic syntax of a JavaScript object is:

let objectName = {
    property1: value1,
    property2: value2,
    property3: value3
};

Example of Object:

let car = {
    brand: "Tata",
    model: "Nexon",
    year: 2024
};

Creating Objects in JavaScript

There are multiple ways to create objects in JavaScript.

1. Object Literal

This is the most common and easiest method.

Example:

let person = {
    name: "John",
    age: 35
};

2. Using new Object()

Create an object through a new keyword.

let person = new Object();

person.name = "John";
person.age = 35;

3. Using a Constructor Function

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

let user = new Person("John", 35);

4. Using ES6 Class

class Person {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
}

let user = new Person("John", 35);

Accessing Object Properties

JavaScript provides two ways to access object properties.

1. Dot Notation

let person = {
    name: "John",
    age: 35
};
console.log(person.name);

Output:

2. Bracket Notation

Bracket notation is useful when property names contain spaces or special characters.

let person = {
    name: "John",
    age: 35
};
console.log(person["age"]);

Output:

Adding Properties to the Object

let person = {
    name: "John"
};

person.age = 35;

console.log(person);

Output:

Updating Properties to Object

Existing properties can be modified easily.

let person = {
    name: "John",
    age: 35
};

person.age = 40;

console.log(person.age);

Output:

Deleting Properties from the Object

The delete keyword removes a property from an object.

let person = {
    name: "John",
    age: 35
};

delete person.age;

console.log(person);

Output:

What are Nested Objects?

Objects that contain other objects are called nested objects.

let employee = {
    name: "John",

    address: {
        city: "New Delhi",
        country: "India"
    }
};
console.log(employee.address.city);

Output:

What is Object.keys()

It is used to return all property names.

let person = {
    name: "John",
    age: 35
};

console.log(Object.keys(person));

Output:

What is Object.values()

It is used to return all values.

let person = {
    name: "John",
    age: 35
};

console.log(Object.keys(person));

Output:

What is Object.entries()

It is used to return key-value pairs.

let person = {
    name: "John",
    age: 35
};

console.log(Object.entries(person));

Output:

Real-life Example:

Imagine you are developing an online shopping website.

let product = {
    id: 101,
    name: "Laptop",
    price: 65000,
    brand: "HP",
    inStock: true
};

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

Output:

Common Mistakes

1. Using Dot Notation with Spaces

Wrong:

let user = {
    "full name": "John"
};

console.log(user.full name);

Correct:

let user = {
    "full name": "John"
};

console.log(user["full name"]);

2. Forgetting Quotes Around Special Property Names

Wrong:

let person = {
    full name: "John"
};

Correct:

let person = {
    "full name": "John"
};

3. Using Assignment Instead of Comparison

Wrong:

if(person.age = 18) {
    console.log("Adult");
}

Correct:

if(person.age === 18) {
    console.log("Adult");
}

4. Accessing Non-Existing Properties

let person = {
    name: "John"
};

console.log(person.age);

Output:

Note: Always verify whether a property exists.

let person = {
    name: "John"
};

if(person.age !== undefined) {
    console.log(person.age);
}

5. Forgetting Commas Between Properties

Wrong:

let person = {
    name: "John"
    age: 35
};

Correct:

let person = {
    name: "John",
    age: 35
};

Javascript Object – Interview Questions

Javascript Object – Objective Questions (MCQs)

Conclusion

JavaScript Objects are one of the most powerful and essential features of the language. They allow developers to store related data and functionality in a structured way. Objects can contain properties, methods, arrays, and even other objects, making them highly flexible and useful for building real-world applications.

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