JavaScript Playground

Write, run, and share code snippets — no setup required.

index.js

Alice
30

Output

Click Run to see the output here.

const fs = require('fs');
const [name, ageStr] = fs
    .readFileSync(0, "utf8")
    .trim()
    .split('\n');
const age = parseInt(ageStr, 10);
console.log(`Hello, ${name}! You are ${age} years old.`);

Run JavaScript online in your browser

A free online JavaScript playground. Write modern ES2022+ JS in your browser, hit Run, and the code executes on Node 24 or Deno 2.4 in seconds. No install, no npm, no package.json to scaffold first.

The editor is built on the same engine as VS Code, so JS syntax highlighting, autocompletion, and error squiggles all work. Your code runs on Node 24 (or Deno 2.4.3) inside a sandboxed container, with modern ES2022+ features, Node's fs/http APIs, and Deno's standard library available — handy when you want to test an async function, run a JSON fetch, or step through an interview problem without leaving the page.

What makes this JavaScript playground useful

Instant JavaScript execution — write code, press Run, and see output from Node 24 (or Deno 2.4) in seconds, no setup needed.
Full JavaScript syntax highlighting, autocompletion, and error messages, powered by the same editor engine as VS Code, right in your browser.
Stdin input is wired into process.stdin (Node) and the Deno readLine pattern. Type lines into the input box and the playground feeds them in order. No Node, npm, or package.json to configure on your end.
Deno 2.4.3 + Node 24 runtime — modern ES2022+ JavaScript with Node APIs and Deno's standard library, no package.json needed.

What you can build in the JavaScript playground

Array methods (map, filter, reduce), async/await, destructuring, and modern ES2022+ idioms, run on Node 24 or Deno 2.4.
Fetching and parsing JSON, promises and async flows, class syntax, and quick algorithm problems for interview practice.
One-off snippets: test a regex, verify a date format, try a new Array method, or confirm a tricky destructuring pattern.

Online JavaScript playground FAQ

Is the online JavaScript playground free?

Yes, the online JavaScript playground is free to use. There's no sign-up, no Node install, and no npm setup — open the page and run code on Node 24 or Deno 2.4.

Do I need Node.js installed to run JavaScript online?

No install needed. You don't need Node, npm, or a package.json on your machine. The online JavaScript runner executes your code on Node 24 (or Deno 2.4) and returns the output in seconds.

Does the JavaScript playground work on mobile and Chromebooks?

Yes. The JavaScript playground runs in any modern browser, on desktop, tablet or mobile. It's a good option for running JS from a Chromebook, iPad, or school computer where you can't install Node.

Can I read stdin from Node in the JavaScript playground?

Yes. Lines you type into the stdin input box are piped to process.stdin on Node, so readline interfaces and for await (const line of process.stdin) loops behave the same as running node script.js locally and pasting input at the terminal.

How do I learn JavaScript after trying the playground?

Edit the sample JavaScript, press Run, and iterate. When you want something more structured, Coddy's interactive JavaScript course takes you from variables to closures, prototypes, and async/await.