Code Quiz

Timeout Wrapper Timer Leak

A Promise.race timeout helper looks correct but leaks a timer that keeps firing after the race is decided.

Codejavascript

function withTimeout(promise, ms) {
  let timer;
  const timeout = new Promise((_, reject) => {
    timer = setTimeout(() => reject(new Error('timeout')), ms);
  });
  return Promise.race([promise, timeout]);
}

// usage
const data = await withTimeout(fetchData(), 3000);

This wrapper resolves/rejects correctly in the happy path, but it has a real resource/cleanup bug. What is it and how do you fix it?

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