How to run JavaScript

Try the browser console

Open your browser's developer tools, select Console, enter an expression, and press Enter. The console is ideal for short experiments.

2 + 3
console.log("JavaScript is ready");

Run a script in a page

Save these files together, open index.html, and inspect both the page and console. defer waits until the HTML has been parsed.

<!-- index.html -->
<p id="status">Waiting...</p>
<script src="app.js" defer></script>

// app.js
document.querySelector("#status").textContent = "Running!";

Run JavaScript with Node.js

Install a current Node.js release, save the code as app.js, and run it from that directory. Node has no page or document object.

// app.js
const message = "Hello from Node.js";
console.log(message);

// Terminal:
node app.js

Choose the right environment

• Use the console for quick checks
• Use a script element for browser behavior and DOM work
• Use Node.js for command-line programs, servers, and tooling
• Check versions with node --version and keep developer tools open while learning