Why race conditions survive normal review
A React race condition usually appears when an older async request resolves after a newer one, then overwrites the UI with stale data. The component often looks fine in a static diff because the bug is about timing, not syntax.
AI-generated React code makes this worse because it often reaches for the quickest possible effect pattern: fetch in useEffect, set state when the promise resolves, and hope the component identity never changes fast enough to expose the flaw.
The first rule is ownership, not cleanup trivia
Before you add guards, decide which request owns the right to update the screen. That is the real contract. If the route param, selected record, or search query changes, the old request should lose authority immediately.
Once that ownership rule is explicit, the implementation becomes much simpler to judge.
- Cancel requests when the platform allows it instead of only hiding late results.
- Track the latest request identity when cancellation is not available.
- Do not let stale promises write loading, success, or error state after the source input changed.
Patterns that usually hold up in production
An AbortController is the cleanest option when the fetch layer supports it. It aligns the browser request lifecycle with the component lifecycle instead of pretending late responses are harmless.
If the async path cannot be cancelled, gate the resolution with a request token or monotonically increasing sequence id. The important part is that the component can explain why one result is still valid and another is not.
How to prove the fix is real
Do not stop after the warning disappears. Test rapid input changes, delayed responses, and unmount during an in-flight request. Those are the moments where race conditions reappear.
A good regression test intentionally returns results out of order. If the UI still renders the newest state and the old request cannot flash stale content, the fix is probably real.