Next.jshard

Explain caching and revalidation in Next.js (fetch cache, revalidatePath).

Answer

Next.js caches server fetches by default based on request and route settings. You can opt out with cache: 'no-store' or set a revalidate time to refresh data periodically. revalidatePath/revalidateTag let you invalidate cached pages or data on demand.

export const revalidate = 60

const res = await fetch('https://api.example.com/posts', { next: { revalidate: 60 } })
const posts = await res.json()

Advanced answer

Deep dive

Expanding on the short answer — what usually matters in practice:

Context (tags): caching, revalidation, fetch, nextjs
Lifecycle: what happens at runtime (render/build, request/response, background jobs).
Caching: where cache lives, cache keys, how to invalidate without chaos.
Security: authn/authz, secrets, attack surface (SSRF/CSRF).
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

Here’s an additional example (building on the short answer):

export const revalidate = 60

const res = await fetch('https://api.example.com/posts', { next: { revalidate: 60 } })
const posts = await res.json()

Common pitfalls

Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).
Ignoring constraints: memory, concurrency, network/disk costs.

Interview follow-ups

When would you choose an alternative and why?
What production issues show up and how do you diagnose them?
How would you test edge cases?