Question 1

What is proxy.ts in Next.js 16 and how do you migrate from middleware.ts?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know what an HTTP redirect and rewrite are.
**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 (`file-conventions/proxy`, `middleware`, the version 16 guide) and, in the **Verified** section, against `next build`, `next start` and `curl` in a 16.4.2 lab.

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Question 2

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 3

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 4

How do View Transitions work with next/link transitionTypes in Next.js 16.2?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know `<Link>` and basic CSS animations.
**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 `link` reference and the view transitions guide) and, in the **Verified** section, by driving a 16.4.2 lab in Chromium 141 with Playwright and recording every `doc

Question 5

What is the difference between revalidateTag(), updateTag(), and refresh() in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know what a Server Action and a cache tag are.
**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 in `node_modules/next/dist/docs/` and, in the **Verified** section, against a 16.4.2 lab measured with `curl` and with Playwright clicking real buttons i

Question 6

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 7

How do you enable and evaluate the React Compiler in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know React state and re-rendering.
**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 (`reactCompiler`, `turbopackRustReactCompiler`, the version 16 guide) and, in the **Verified** section, against three builds of the same 16.4.2 lab app with render counts re

Question 8

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 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

How does prefetching and navigation caching work in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know `<Link>` and the App Router.
**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 (the prefetching guide, `partialPrefetching`, `prefetch`, `navigation`, `ensureStatic`) and, in the **Verified** section, against prefetch requests recorded by Playwright in Ch

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