Question 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 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 are dynamic routes and catch-all segments 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 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 Firs

NEXT.JSDECODED.

Easy

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

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?

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 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 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?

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

What is the Full Route Cache in Next.js?

How do you set security headers and a nonce-based Content Security Policy in Next.js?

Partial Prerendering (PPR) — how do you enable it incrementally?