Run TypeScript online

TypeScript is JavaScript with a serious type system: interfaces, generics, mapped types, conditional types. It compiles to JS and runs on Node — you get type-safety at compile time and JavaScript's ecosystem at runtime.

ls-judge compiles TypeScript 5 with tsc and runs the emitted JS on Node inside a Firecracker microVM.

What you get in TypeScript

Clicking "Run now" opens the playground with this exact code and a matching test case pre-loaded — 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');
});

Common questions about TypeScript on ls-judge

Which TS?

TypeScript 5.x — with strict mode by default.

Which Node?

A recent LTS (see /lang/javascript for details).

npm packages?

No network — bring bundled source.

ts-node vs tsc + node?

We compile with tsc and run the emitted JS — more predictable than ts-node under a strict sandbox.

• TypeScript documentation↗