Question 1

How do you handle forms with Server Actions in Next.js (progressive enhancement)?

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 next/script and what are its strategy options 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 3

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 4

How do Next.js Devtools MCP and AGENTS.md change AI-assisted debugging?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — no prior knowledge of MCP needed.
**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 AI agents and MCP guides, `agentRules`, `agentFeedback`) and, in the **Verified** section, against a 16.4.2 `next dev` server: its terminal, the files it wrote, and JSON-RPC calls t

Question 5

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 6

What is the 'use client' directive and when do you need it?

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

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

How do you handle forms with Server Actions in Next.js (progressive enhancement)?

What is next/script and what are its strategy options in Next.js?

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

How do Next.js Devtools MCP and AGENTS.md change AI-assisted debugging?

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

What is the 'use client' directive and when do you need it?

Hard

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