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

How does file-based routing work 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:** 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 difference between Server Components and Client Components 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 5

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 6

How does Next.js decide between static and dynamic rendering at build time?

Accepted Answer

At build, Next.js **analyzes each route**: if it uses no dynamic functions and only cached data, it's **prerendered statically**; if it uses cookies()/headers()/searchParams or **uncached** fetches, it's marked **dynamic**. Segment config (dynamic) can force either mode.

Question 7

How do you read cookies and headers in Next.js (cookies(), headers())?

Accepted Answer

**Target Audience:** Developers preparing for Next.js interviews — assumes basic App Router knowledge (Server Components, Server Actions).
**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, `curl` requests to `next start` and a Chromium browser.

## 1. Why This Even

Question 8

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 9

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 10

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

NEXT.JSDECODED.

Easy

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

How does file-based routing work in the Next.js App Router?

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

Medium

What is the difference between Server Components and Client Components in Next.js?

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

How does Next.js decide between static and dynamic rendering at build time?

How do you read cookies and headers in Next.js (cookies(), headers())?

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

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

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

App Router 15 — why are params and searchParams now Promises?

Hard

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

What changed about caching defaults in Next.js 15?

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

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

What is the Full Route Cache in Next.js?