Question 1

How does client-side navigation work in Next.js (next/link and useRouter)?

Accepted Answer

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

> **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 browser.

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

Question 2

next/font and next/image — how do they combine for Core Web Vitals?

Accepted Answer

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

> **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 block

Question 3

What is Next.js and what problems does it solve?

Accepted Answer

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

> **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 block

Question 4

What is the next/form Form component and when would you use it?

Accepted Answer

**Target Audience:** Beginners preparing for Next.js interviews — assumes you know what an HTML form and a URL query string are.
**Difficulty:** Easy

> **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 a lab app served by `next start` and submitted in a real Chromium browser with JavaScript on and off.

Question 5

How do sitemap.ts and robots.ts work in Next.js?

Accepted Answer

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

> **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 block

Question 6

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 7

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 8

What is generateStaticParams in Next.js and how does it enable SSG for dynamic routes?

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

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 10

Caching defaults in Next 15 — what is no longer cached by default?

Accepted Answer

Next 15 makes `fetch` and `GET` Route Handlers dynamic by default — add `cache: 'force-cache'` / `'use cache'` or `export const dynamic = 'force-static'` to re-cache.

NEXT.JSDECODED.

Easy

How does client-side navigation work in Next.js (next/link and useRouter)?

next/font and next/image — how do they combine for Core Web Vitals?

What is Next.js and what problems does it solve?

What is the next/form Form component and when would you use it?

How do sitemap.ts and robots.ts work in Next.js?

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 generateStaticParams in Next.js and how does it enable SSG for dynamic routes?

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

Caching defaults in Next 15 — what is no longer cached by default?

What is the Data Cache in Next.js and how do you opt out of it?

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

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

Hard

How do you migrate from the Pages Router to the App Router in Next.js?

What are React Server Components and why does Next.js use them?

Observability with OpenTelemetry in Next 15 — how is OTEL wired?

What changed about caching defaults in Next.js 15?

How do you handle instrumentation and observability in Next.js (instrumentation.ts)?

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 RSC payload and how does Next.js stream it to the browser?