JavaScript Variables & Types

Explore JavaScript variables, data types, and type coercion through interactive code exercises.

Category: Programming · v1.0.0

Step 1 of 4

Step 1: Declaring Variables

JavaScript has three ways to declare variables:

let — block-scoped, can be reassigned
const — block-scoped, cannot be reassigned
var — function-scoped (older, avoid in modern code)

Try it out — run the code, then experiment by changing values:

Step 2: Data Types

JavaScript has several primitive types. Use typeof to inspect them:

Step 3: Type Coercion

JavaScript automatically converts types in certain situations. This can lead to surprising results!

The == operator coerces types. === (strict equality) does not.

About This Lab

Variables are the building blocks of any program. In this lab, you'll learn how to declare variables with let, const, and var, understand JavaScript's core data types (strings, numbers, booleans, arrays, objects), and see how type coercion works. Each step includes a live code editor so you can experiment and see results instantly.

How It Works