How do you cancel async work?

Promises have no cancel method. A promise only reports an outcome, so you cancel the work, with a signal that the work agrees to watch.

• AbortController owns the switch. controller.signal is an AbortSignal you hand out. controller.abort(reason) sets signal.aborted to true, stores signal.reason, and fires an abort event once. abort() with no reason uses an AbortError DOMException.
• APIs that accept { signal } do the rest. fetch rejects with signal.reason, and Node's timers/promises, events.once and streams accept signals too.
• Your own functions must cooperate. Check signal.throwIfAborted() at the start and between steps, add an abort listener to stop timers or requests, reject with signal.reason, and remove the listener when done.
• AbortSignal.timeout(ms) returns a signal that aborts after ms with a TimeoutError. It is the clean replacement for Promise.race with a timer, because it cancels the work.
• AbortSignal.any([a, b]) returns a signal that aborts when any input aborts, with that input's reason. Use it to combine a user cancel with a timeout. Both static methods exist in Node 24; browsers support them in current versions (check MDN's compatibility table for older ones).
• Aborting is cooperative. If the work ignores the signal, it keeps running. Abort only changes work that is built to listen.

function sleep(ms, { signal } = {}) {
  return new Promise((resolve, reject) => {
    signal?.throwIfAborted();
    const timer = setTimeout(() => {
      signal?.removeEventListener('abort', onAbort);
      resolve();
    }, ms);
    function onAbort() {
      clearTimeout(timer);
      reject(signal.reason);
    }
    signal?.addEventListener('abort', onAbort, { once: true });
  });
}

const controller = new AbortController();
setTimeout(() => controller.abort(), 20);
try {
  await sleep(1000, { signal: controller.signal });
} catch (error) {
  console.log(error.name, '|', error.message, '|', controller.signal.aborted);
}
// → AbortError | This operation was aborted | true

• Using Promise.race([work, timeout]) and calling it cancellation. The loser keeps running. Pass AbortSignal.timeout(ms) to the work.
• Catching every error and treating it as a failure. An abort rejects too. Check error.name === 'AbortError' (or 'TimeoutError') and handle it as an expected outcome, not an incident.
• Reusing an aborted controller. A signal aborts once and stays aborted. Create a new AbortController for the next operation, such as for each search keystroke.
• Leaving an abort listener on a long-lived signal. Pass { once: true } and remove the listener when the work finishes, or the listener stays registered for as long as the signal lives.