Variables in JavaScript

Learn how to store and manage data using variables.

What are Variables?

Variables are containers for storing data values. In JavaScript, you can declare variables using three keywords: var, let, and const.

Modern JavaScript: Use let and const instead of var. They provide better scoping and help prevent bugs.

Declaring Variables

Using let

Use let when you need to reassign a variable later.

Try it yourself

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Using const

Use const for values that should never be reassigned.

Try it yourself

Output

Using var (Legacy)

var is the old way to declare variables. It has function scope instead of block scope, which can lead to unexpected behavior.

JavaScript

var oldStyle = "I'm function-scoped";
// Avoid using var in modern JavaScript

Data Types

JavaScript has several data types:

Explore data types

Output

Variable Naming Rules

Names can contain letters, digits, underscores, and dollar signs
Names must begin with a letter, underscore (_), or dollar sign ($)
Names are case-sensitive (myVar and myvar are different)
Reserved words (like let, const, function) cannot be used as names

JavaScript

// Good variable names
let userName = "John";
let user_age = 25;
let $price = 9.99;
let _private = "hidden";

// Use camelCase for multi-word names
let firstName = "Jane";
let totalItemCount = 42;

Challenge: Create Your Variables

Create variables to store your name, age, and a boolean indicating if you like JavaScript. Then log them to the console.

Your solution

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