Question 1

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 2

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 3

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

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 is hydration in Next.js and what causes a hydration error?

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

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 6

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 7

How do you debug Server Functions and hydration mismatches in Next.js 16.2?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know Server Actions and what hydration is.
**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 (`logging`, the debugging guide, the hydration guide) and, in the **Verified** section, against real `next dev` and `next start` output from a 16.4.2 lab driven by P

Question 8

How does Next.js handle SEO compared to a client-rendered SPA?

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

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know what a Server Component is.
**Difficulty:** Hard

> **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 real output from `next build`, `next start` and `curl` in a 16.4.2 lab.

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Question 10

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

Accepted Answer

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

> **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

NEXT.JSDECODED.

Medium

What is the difference between static and dynamic rendering 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?

What is hydration in Next.js and what causes a hydration error?

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

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

How do you debug Server Functions and hydration mismatches in Next.js 16.2?

How does Next.js handle SEO compared to a client-rendered SPA?

Hard

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

What is Partial Prerendering (PPR) 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?