JavaScript Variables Explained (var, let, const) – Complete Guide | TechYantram

Introduction

JavaScript is one of the most popular programming languages, and variables are its foundation. Without variables, you cannot store or manipulate data in your application.

In this guide by TechYantram, you will learn everything about JavaScript variables including var, let, const, scope, hoisting, and best practices.

What is a Variable in JavaScript?

A variable is a container used to store data values.

let company = "TechYantram";

Here:

• company → variable name
• "TechYantram" → value

 Types of Variables in JavaScript

🔹 var (Old Method)

var age = 25;

• Function scoped
• Can be redeclared
• Hoisted

🔹 let (Modern Method)

let city = "Delhi";

• Block scoped
• Cannot be redeclared
• Can be updated

🔹 const (Constant)

const pi = 3.14;

• Block scoped
• Cannot be reassigned
• Best for fixed values

Difference Between var, let, const

 Variable Naming Rules

• Must start with letter, $, or _
• Cannot start with number
• Case-sensitive
• Avoid reserved keywords

let userName = "Goutam";

Dynamic Typing

JavaScript is dynamically typed:

let value = 10;
value = "Hello";
value = true;

 Variable Scope

Global Scope

let globalVar = "Available everywhere";

Block Scope

{
  let blockVar = "Inside block";
}

Function Scope

function demo() {
  var x = 10;
}

 Hoisting Explained

console.log(a); // undefined
var a = 5;
console.log(b); // Error
let b = 10;

Real Example

const user = "Goutam";
let balance = 1000;

balance += 500;

console.log(`${user} has ₹${balance}`);

 Best Practices

• Use const by default
• Use let when needed
• Avoid var
• Use meaningful names
• Follow camelCase

Common Mistakes

• Using var
• Redeclaring variables
• Ignoring scope
• Poor naming