Q: How do you revalidate data after a mutation in Next.js?

After a Server Action mutates data, call revalidatePath() or revalidateTag() to invalidate the affected caches, or router.refresh() on the client, so the UI reflects the change. Redirecting with redirect() also re-renders the target route fresh. <text

Question 1

What changed for next/image defaults in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you have used `next/image`.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js 16.4.2 docs (the `image` reference and the version 16 guide) and the built-in defaults in `next/dist/shared/lib/image-config.js`, and, in the **Verified** section, against `curl` requests to the i

Question 2

What is the difference between static and dynamic rendering in the Next.js App Router?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 3

How do you fetch data in Next.js Client Components (SWR, React Query, use)?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 4

How do you revalidate data after a mutation in Next.js?

Accepted Answer

After a Server Action mutates data, call revalidatePath() or revalidateTag() to invalidate the affected caches, or router.refresh() on the client, so the UI reflects the change. Redirecting with redirect() also re-renders the target route fresh.

Question 5

How do Server Actions differ from Route Handlers in Next.js?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 6

PPR vs ISR vs SSR — how do you pick the rendering strategy in Next 15?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 7

What is on-demand revalidation in Next.js (revalidatePath / revalidateTag)?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 8

What are the rendering strategies in Next.js (SSR, SSG, ISR, CSR)?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 9

revalidateTag vs revalidatePath — when to use which?

Accepted Answer

`revalidateTag` purges by Data Cache tag wherever it is used; `revalidatePath` purges a specific route — prefer tags for CMS content, path for page-centric invalidation.

Question 10

What is after() in Next.js and when should you use it?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js 16.4.2 docs shipped with the package and, in the **Verified** section, against real output from a build or a running server.

## 1. Why This Even Matters — A Story First

At a good caf

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Medium

What changed for next/image defaults in Next.js 16?

What is the difference between static and dynamic rendering in the Next.js App Router?

How do you fetch data in Next.js Client Components (SWR, React Query, use)?

How do you revalidate data after a mutation in Next.js?

How do Server Actions differ from Route Handlers in Next.js?

PPR vs ISR vs SSR — how do you pick the rendering strategy in Next 15?

What is on-demand revalidation in Next.js (revalidatePath / revalidateTag)?

What are the rendering strategies in Next.js (SSR, SSG, ISR, CSR)?

Hard

What are the caching layers in Next.js (Request Memoization, Data Cache, Full Route Cache, Router Cache)?

What is the Full Route Cache in Next.js?