Run Node.js 20 online

What's in Node.js 20

• Permission model (experimental): restrict filesystem, network and process access.
• Single-executable applications: bundle a Node script into a stand-alone binary.
• Test runner and mocking APIs stable.

What you get in Node.js 20

Clicking "Run now" opens the playground with this exact code and a matching test case — passes on first Run.

const lines = [];
process.stdin.on('data', d => lines.push(d.toString()));
process.stdin.on('end', () => {
  const n = parseInt(lines.join('').trim());
  console.log(n * 2);
});

How ls-judge runs Node.js 20

Every submission is compiled and executed inside its own Firecracker microVM — the same isolation primitive AWS Lambda uses. No shared container, no shared kernel with other users' code. The Node.js 20toolchain shipped with the microVM is the real thing (not a browser-side emulation): syscalls behave the way they do in production, and the compile / runtime behaviour matches what you would see on your own machine with that version installed.

Feed stdin from the Tests panel, watch verdicts stream per test case over a WebSocket. Free to use, no sign-up, works from any browser.