Silent Failures in Request Cancellation: The AbortController Pitfalls Most Developers Ship

AbortController has been available in all modern JavaScript environments for years, yet most implementations still handle request cancellation incorrectly in ways that only surface under production stress—flaky networks, rapid user interactions, and concurrent requests. Understanding that cancellation (AbortError) is a normal control-flow outcome, not an exception, and mastering modern patterns like AbortSignal.timeout() without memory leaks, separates code that works in demos from code that ships without silent failures and state corruption.