AbortController

                const controller = new AbortController(); fetch(url, { signal: controller.signal }); controller.abort();
              

Purpose

AbortController provides a signal that can be passed to fetch (and other cancellation-aware APIs) to cancel an in-flight operation on demand, via controller.abort().

Syntax

const controller = new AbortController();

fetch('/api/search?q=term', { signal: controller.signal })
  .then((response) => response.json())
  .catch((error) => {
    if (error.name === 'AbortError') {
      console.log('Cancelled — expected, not a failure.');
    } else {
      throw error;
    }
  });

controller.abort(); // cancels the fetch above

Behavior notes

• controller.signal can be reused across multiple operations if they should all cancel together — calling abort() once cancels every operation currently using that signal.
• A cancelled fetch’s promise rejects with an error whose .name is "AbortError" — this should usually be treated as an expected outcome (the request was intentionally cancelled), not logged or surfaced as a genuine failure.
• AbortSignal.timeout(ms) creates a signal that aborts automatically after a delay — a convenient shortcut for a request-timeout pattern without manually wiring up a setTimeout.
• Cancelling a request that’s already completed has no effect; abort() is safe to call even if the operation already finished.

Common mistakes

• Treating an AbortError the same as a genuine network failure in error-handling/logging code, producing noisy false-positive error reports for intentional cancellations.
• Forgetting to cancel a stale request when a newer one starts (search-as-you-type, for instance), leaving a race condition where the stale response can still arrive and overwrite newer state.

Runtime notes

Standard in every current browser; available as a global in Node 15 and later.