startTransition for responsive UI
When should you use startTransition / useDeferredValue in React 18/19?
Answers use simple, clear English.
Audio N/AQuick interview answer
Use them to keep urgent updates (typing, clicking) responsive while deferring expensive UI work (filtering large lists, heavy charts). startTransition marks state updates as non-urgent; useDeferredValue defers a derived value. Pair with Suspense where appropriate.
Detailed answer
Use them to keep urgent updates (typing, clicking) responsive while deferring expensive UI work (filtering large lists, heavy charts). startTransition marks state updates as non-urgent; useDeferredValue defers a derived value. Pair with Suspense where appropriate. Don't wrap every update — only expensive ones.
Real example & use case
Search box updates immediately; filtered 10k-row table uses deferred query.
Pros & cons
Pros: better INP. Cons: UI can briefly show stale deferred results.