Variables in JavaScript: 7 Powerful Facts to Understand var, let, and const

Introduction

If you are starting your web development journey, learning Variables in JavaScript is one of the first and most important steps. Variables are like containers in which data is stored. Everything you build—web apps, games, UI interactions—depends on how well you handle variables.

Because JavaScript powers almost every website today, understanding how variables work makes your foundation strong and helps you code better.

 

What Are Variables in JavaScript

Variables in JavaScript store values such as numbers, text, objects, or functions. When you create a variable, you are simply giving a name to a piece of data so that JavaScript can remember and use it later.

Example:

let userName = “Sumit”;

Here, userName is a variable storing the text “Sumit”.

Understanding variables helps beginners organize code and perform actions like calculations, storing user input, and displaying data on websites.

 

Why Variables Matter in Web Development

Every interactive feature on the web depends on variables. Without variables, you cannot:

• Store user input
• Update UI elements
• Handle form data
• Build games
• Manage application states
• Create dynamic websites

In simple words, variables allow JavaScript to think, remember, and make decisions.

For example, if a user logs in, a variable stores their name or login status. A website cannot function without variables.

 

Types of Variables in JavaScript

JavaScript allows you to create variables in three ways:

• var
• let
• const

All three store values, but they behave differently. Each one is designed for a specific use case, and choosing the right one improves your code quality.

This is why learning Variables in JavaScript is essential before moving to advanced topics like functions, DOM manipulation, or APIs

 

Understanding var

var is the oldest way to create variables in JavaScript. It has been used since the beginning of the language. But today, developers use it less because it has limitations.

• Characteristics of var:
• Function-scoped
• Can be redeclared
• Can be updated

Not recommended for modern coding

Example:

var age = 20;

var age = 25; // Allowed

Why it’s not preferred:

var can create bugs because it allows redeclaration and does not respect block scope like if/else or loops.

 

Understanding let

let was introduced in ES6 (2015) and is now the most commonly used variable type.

Characteristics of let:

1. Block-scoped
2. Can be updated
3. Cannot be redeclared in the same scope
4. Safer and better than var

Example:

let score = 10;

score = 15; // Allowed

But this is not allowed:

let score = 10;

let score = 20; // Error

This prevents mistakes and makes your code more predictable.

 

Understanding const

const is used for values that should not change once assigned.

Characteristics of const:

1. Block-scoped
2. Cannot be updated
3. Cannot be redeclared
4. Ideal for constants and fixed values

Example:

const pi = 3.14;

You cannot change it later:

pi = 4; // Error

But note this:

If const stores an object or array, the internal values can change, but the variable name cannot be reassigned.

Example:

const user = { name: “Sumit” };

user.name = “Ravi”; // Allowed

 

Real-World Examples of Variables in JavaScript

Example 1: Storing user data

let userName = “Aman”;

let userLoggedIn = true;

 

Example 2: Updating a shopping cart

let items = 3;

items = items + 1; // User adds one more item

 

Example 3: Website theme toggle

let theme = “light”;

theme = “dark”;

 

Example 4: Fixed application settings

const appVersion = “1.0.0”;

Variables control everything—from UI updates to logic handling.

 

Best Practices for Beginners

To write clean and modern JavaScript code, follow these rules:

1. Prefer let over var
2. let is safer and avoids bugs.
3. Use const for fixed values
4. It prevents accidental changes.
5. Use meaningful names

Bad:

let x = 10;

 

Good:

let itemCount = 10;

 

Avoid using var

• Modern JavaScript rarely needs it.
• Keep variables in the smallest scope
• Declare inside functions or blocks instead of global scope.
• These practices help you write clean, maintainable code that professionals expect.

 

Conclusion

Understanding Variables in JavaScript is the foundation of becoming a strong JavaScript developer. Knowing how var, let, and const behave prepares you for real-world projects, whether you are building websites, apps, or interactive features.

Variables make your code logical, structured, and easy to manage. If you want to grow as a developer, mastering variables is your first major step.

 

External Link (DoFollow)

Learn more:

MDN JavaScript Guide

 

FAQs

 

1. Which variable type should beginners use?

Use let for most cases and const for fixed values. Avoid var.

2. Can const variables store objects?

Yes. You cannot reassign the object, but you can change its internal values.

3. Is var still used today?

It works, but modern developers rarely use it because let and const are safer.

4. Are variables case-sensitive?

Yes. UserName and username are different variables.

5. Do I need to declare variables before using them?

Yes. Always declare variables first to avoid errors.