JavaScript Variables: var, let & const

Variables are the building blocks of any programming language. In JavaScript, you use them to store data, reuse values, and write clean, maintainable code. Let's break down the three ways to declare variables in JavaScript: var, let, and const.

1. What Are Variables?

A variable is like a container that holds a value — it could be a number, text, object, or more. Think of it like naming a box so you know what’s inside.

let name = "Alice";
const age = 25;
var city = "New York";

2. The Old Way: var

var was the only way to declare variables before ES6 (2015). It's function-scoped and allows redeclaration — but that can lead to bugs.

var score = 10;
var score = 20; // ✅ allowed

function testVar() {
  var x = 1;
  if (true) {
    var x = 2;
    console.log(x); // 2
  }
  console.log(x); // 2
}

3. The Better Way: let

Use let when the value of your variable might change. It’s block-scoped, so it behaves better inside loops and conditionals.

let count = 1;
count = 2; // ✅ allowed

if (true) {
  let count = 3;
  console.log(count); // 3
}
console.log(count); // 2

4. The Constant Way: const

Use const when your variable should never change. It must be assigned a value when declared and can’t be reassigned.

const pi = 3.14;
// pi = 3.14159; ❌ Error

const user = { name: "John" };
user.name = "Jane"; // ✅ allowed (object values can change)

5. Comparison Table

6. Final Tips

• Use const by default unless you need to reassign.
• Use let when the value changes.
• Avoid var unless working on legacy projects.