Objects in JS

 In JavaScript, objects are one of the most important data structures. They allow you to store data in key–value pairs and represent real-world entities — like users, products, or configurations — in a structured way.

Objects are everywhere in JavaScript — from browser APIs to JSON data, and even built-in features like Math and Date. Let’s explore them step by step.

What Is an Object?

An object in JavaScript is a collection of properties, where each property has a key (name) and a value.

Syntax

let objectName = {  key1: value1,  key2: value2,  key3: value3};

Each key is a string (or symbol), and each value can be any data type — a number, string, boolean, array, another object, or even a function!

Example

Let’s create a simple person object:

let person = {  name: "Harry",  age: 22,  isStudent: true};

Here:

• "name" is a key with the value "Harry".
• "age" is a key with the value 22.
• "isStudent" is a key with the value true.

Accessing Object Properties

There are two ways to access properties of an object:

1. Dot Notation

console.log(person.name); // Output: Harry

2. Bracket Notation

console.log(person["age"]); // Output: 22

Use dot notation when you know the property name beforehand. Use bracket notation when the property name is dynamic or stored in a variable.

Example with Dynamic Property

let key = "isStudent";console.log(person[key]); // Output: true

Here, since the key is stored in a variable, we must use bracket notation.

Modifying and Adding Properties

You can modify existing properties or add new ones anytime — objects in JavaScript are mutable.

Modify a Property

person.age = 23;console.log(person.age); // Output: 23

Add a New Property

person.city = "Delhi";console.log(person.city); // Output: Delhi

Deleting Properties

To remove a property from an object, use the delete operator:

delete person.isStudent;console.log(person);// Output: { name: "Abhinav", age: 23, city: "Delhi" }

Nested Objects

Objects can contain other objects — allowing you to represent complex data structures.

let user = {  name: "Riya",  address: {    city: "Mumbai",    zip: 400001  }}; console.log(user.address.city); // Output: Mumbai

You can nest objects as deeply as needed.

Objects and Functions

Functions can be stored inside objects — these are called methods.

let calculator = {  add: function(a, b) {    return a + b;  },  subtract(a, b) {    return a - b; // shorthand syntax  }}; console.log(calculator.add(5, 3));      // 8console.log(calculator.subtract(10, 4)); // 6

This is one of the key features that makes objects so versatile in JavaScript.

Looping Through an Object

You can iterate through an object’s properties using a for...in loop.

let car = {  brand: "Tesla",  model: "Model 3",  year: 2023}; for (let key in car) {  console.log(key + ": " + car[key]);}

Output:

brand: Tesla
model: Model 3
year: 2023

Useful Object Methods

JavaScript provides several built-in methods to work with objects:

Method	Description
Object.keys(obj)	Returns an array of all keys in the object.
Object.values(obj)	Returns an array of all values in the object.
Object.entries(obj)	Returns an array of key–value pairs.
Object.assign(target, source)	Copies properties from one object to another.
Object.freeze(obj)	Prevents changes to the object.

Example

let car = { brand: "Toyota", year: 2020 }; console.log(Object.keys(car));    // ["brand", "year"]console.log(Object.values(car));  // ["Toyota", 2020]console.log(Object.entries(car)); // [["brand", "Toyota"], ["year", 2020]]

Objects vs Arrays

Feature	Object	Array
Structure	Key–value pairs	Indexed list
Order	Unordered	Ordered
Access	By key name	By numeric index
Ideal for	Representing entities (like a user, car, etc.)	Representing lists or sequences

Sometimes, you’ll even combine them — like an array of objects:

let users = [  { name: "Abhinav", age: 22 },  { name: "Priya", age: 25 },  { name: "Rahul", age: 28 }]; console.log(users[0].name); // Output: Abhinav