Run TypeScript 5 online

What's in TypeScript 5

• Standardised (Stage-3) decorators replace TS-only experimental decorators.
• `const` type parameters — infer literal types through generic calls.
• `--isolatedDeclarations` for split-declaration workflows.

What you get in TypeScript 5

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

const lines: string[] = [];
process.stdin.on('data', (d: Buffer) => lines.push(d.toString()));
process.stdin.on('end', () => {
  const n: number = parseInt(lines.join('').trim());
  process.stdout.write((n * 2) + '\n');
});

How ls-judge runs TypeScript 5

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 TypeScript 5toolchain 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.