JavaScript Variables

Variables store information that a JavaScript program can use later.

What Is a Variable?

A variable is a named container that stores a value.

• Variables can store names, ages, prices, and other information.
• JavaScript variables are declared with let, const, or var.

let name = "John";
let age = 25;

• name stores the value John.
• age stores the value 25.

Declaring Variables

Using let

Use let when the value may change later.

let score = 100;

score = 150;

console.log(score);

Output:

150

Using const

Use const when the variable should not be reassigned.

const country = "India";

console.log(country);

Using var

var is the older way to declare variables; prefer let or const.

var city = "Delhi";

Rules for Writing Variables

• Start the name with a letter, underscore (_), or dollar sign ($).
• Numbers are allowed after the first character.
• Spaces and hyphens are not allowed in variable names.
• Do not use keywords such as const, class, or return.
• Names are case-sensitive: userName and username are different.
• Use clear camelCase names, such as totalPrice.

// Valid variable names
let firstName = "Asha";
let _score = 95;
let $price = 499;
let item2 = "Laptop";

// Invalid variable names
// let 2items = 2;       // Cannot begin with a number
// let first-name = "Asha"; // Hyphens are not allowed
// let user name = "Asha";  // Spaces are not allowed
// let class = "JavaScript"; // Reserved keyword

Key Takeaways

• Use const by default and let when the value must change.
• Choose short, clear, and valid variable names.
• Use camelCase for names made from multiple words.