Introduction to JavaScript

JavaScript is the programming language of the web — every browser can run it natively, which is why virtually every interactive website uses it. Unlike Python, which usually needs to be installed separately, JavaScript already runs wherever a browser does.

JavaScript also runs outside the browser, on servers, via Node.js — the same language on the frontend and backend, which is a big part of why it's so widely used.

What JavaScript is actually used for

• Web frontends — every interactive element on a webpage (dropdowns, form validation, live updates) is JavaScript
• Web backends — Node.js lets the same language power servers, APIs, and databases
• Mobile and desktop apps — frameworks like React Native and Electron build real apps from JavaScript
• Scripting and automation — build tools, command-line scripts, and browser extensions

A quick preview

Here's a single line of real JavaScript, executed for real on this page's own compiler — not a mockup:

console.log("Hello from JavaScript!");

Hello from JavaScript!

That's the whole program. The next lesson breaks down exactly what's happening in that line, and has you write your own version.