Next.js: Слои кеширования (request/data/full route) — типичные gotcha на собеседовании

Naming four layers, Next 15 uncached fetch default, memoization ≠ Data Cache, one dynamic API poisons route, revalidate clears Router Cache, router.refresh() — core interview set.

Разбор

• Naming all four + which serves stale. The interview. Seniors point exact layer.
• Next 15 uncached-by-default fetch. Biggest recent gotcha — Next 14 code silently changes on upgrade.
• Request Memoization ≠ Data Cache. One render, fetch-only, always on vs cross-request opt-in. Conflating = common miss.
• Single dynamic API poisons static for whole route. One cookies() → Full Route Cache gone, per-request render.
• revalidatePath/revalidateTag clear client Router Cache for affected routes — after server round-trip; mutation «не видна» until refresh.
• router.refresh() client escape hatch — drop Router Cache, refetch current route server data.

Итог

Cache debugging = identify layer + know Next 15 default flip + invalidation path from Server Action to client refresh.