JavaScript Variables

🧠 What Are JavaScript Variables?

Variables in JavaScript are used to store data values such as text, numbers, or objects.

Think of a variable like a container that holds information.

🏷 Declaring JavaScript Variables

Js uses three keywords to declare variables:

Keyword	Feature
`var`	Old way, function-scoped
`let`	Modern, block-scoped
`const`	Constant (cannot be changed)

✔ Example:

📌 Rules for Naming Variables

Must start with a letter, _ (underscore), or $
Cannot start with a number
Cannot use JavaScript reserved words (like class, return)
JavaScript is case-sensitive (name ≠ Name)

Example:

🧪 Assigning Values

You can declare first, then assign later:

Or declare and assign in one line:

🧮 Changing Variable Values

let and var values can be updated:

But const cannot be changed:

🖥 Js Variables Example with Output

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Variables Example</h2>
<p id="demo"></p>

<script>
let a = 10;
let b = 5;
let sum = a + b;

document.getElementById("demo").innerHTML = "Sum = " + sum;
</script>

</body>
</html>

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Variables Example</h2>

let a = 10;

let b = 5;

let sum = a + b;

document.getElementById("demo").innerHTML = "Sum = " + sum;

</script>

</body>

</html>

Output:

🧭 Summary

Keyword	Can Change Value?	Scope
`var`	✔ Yes	Function scope
`let`	✔ Yes	Block scope
`const`	❌ No	Block scope