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 is the route segment config in Next.js (dynamic, revalidate, runtime)?

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 2

What is Draft Mode in Next.js and how does it work with a headless CMS?

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, a running server or a real Chromium browser. **No real CMS was used:** the lab

Question 3

What is the difference between getServerSideProps/getStaticProps and App Router data fetching?

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

What makes a route dynamic 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 5

How does fetch caching work in the Next.js App Router (force-cache, no-store, revalidate)?

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

What breaks when you upgrade to Next.js 16, and how do you migrate?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — useful for anyone who has to plan a 15 to 16 upgrade.
**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 upgrade guide shipped in `node_modules/next/dist/docs/` and, in the **Verified** section, against real `next build` and `next start` output from a 16.4.2 lab app written i

Question 7

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 8

What is the difference between revalidateTag(), updateTag(), and refresh() in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know what a Server Action and a cache tag are.
**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 in `node_modules/next/dist/docs/` and, in the **Verified** section, against a 16.4.2 lab measured with `curl` and with Playwright clicking real buttons i

Question 9

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 10

What is static export (output: 'export') in Next.js and what does it not support?

Accepted Answer

**Target Audience:** Developers preparing for Next.js interviews — assumes the basics of App Router rendering (static vs dynamic routes).
**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 lab builds with `output: "export"`, a plain static file server and a Chromium browser.

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Medium

What is the route segment config in Next.js (dynamic, revalidate, runtime)?

What is Draft Mode in Next.js and how does it work with a headless CMS?

What is the difference between getServerSideProps/getStaticProps and App Router data fetching?

What makes a route dynamic in the Next.js App Router?

How does fetch caching work in the Next.js App Router (force-cache, no-store, revalidate)?

What breaks when you upgrade to Next.js 16, and how do you migrate?

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

What is the difference between revalidateTag(), updateTag(), and refresh() in Next.js 16?

Hard

What are Server Actions in Next.js and how do they work?

What are Cache Components in Next.js 16 and how does the 'use cache' directive work?

What is Partial Prerendering (PPR) in Next.js?

What is the Router Cache in Next.js and what are its implications?

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

`cacheLife` and `cacheTag` — how do you configure TTL profiles?

unstable_cache vs `cache` (React) — which dedupes what?

What is the Full Route Cache in Next.js?