Introduction to JavaScript

JavaScript is the programming language of the web. Every modern browser runs it, which is why almost every interactive website you use (menus, forms, maps, chat) is powered by JavaScript. It also runs on servers with Node.js, in mobile apps, and in desktop apps like VS Code.

Your first JavaScript

console.log("Hello, world!");
console.log("2 + 2 is", 2 + 2);

console.log() prints a value to the console. It is the first tool every JavaScript developer reaches for, because it shows you exactly what your code is doing.

HTML, CSS and JavaScript

A web page is built from three languages, each with a job:

Language	Job	Example
HTML	structure and content	a heading, a button
CSS	appearance	the button is blue and rounded
JavaScript	behaviour	clicking the button shows a message

Here is all three working together. Press Run, then click the button in the result.

<button id="hi">Say hello</button>
<p id="out"></p>

<script>
  document.getElementById("hi").addEventListener("click", () => {
    document.getElementById("out").textContent = "Hello from JavaScript!";
  });
</script>

Where you'll find JavaScript

Where	Examples
Browsers	Chrome · Firefox · Safari
Servers	Node.js · Bun
Interfaces	React · Vue · Angular
Desktop apps	Electron, which VS Code is built with

Statements and semicolons

A JavaScript program is a list of statements, usually one per line, ending with a semicolon. JavaScript can often guess where a semicolon belongs, but writing them yourself avoids surprises.

let year = 2026;
let launched = 1995;
console.log("JavaScript is", year - launched, "years old");