Question 1

next/font — how does it eliminate layout shift and external requests?

Accepted Answer

`next/font` self-hosts fonts at build, inlines `size-adjust` fallback metrics and subsets, removing Google Fonts requests and CLS.

Question 2

How do metadata files like favicon.ico, icon, opengraph-image and manifest work in Next.js?

Accepted Answer

**Target Audience:** Beginners preparing for Next.js interviews — basic HTML (what the head element is) helps.
**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 a lab app built with `next build`, served with `next start` and inspected with `curl`.

## 1. Why This Even Matters — A

Question 3

What happens when you run next dev, next build and next start?

Accepted Answer

**Target Audience:** Beginners preparing for Next.js interviews — no prior Next.js knowledge assumed.
**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 a real `create-next-app@16.4.2` project run under all three commands and probed with `curl`.

## 1. Why This Even Matters — A St

Question 4

How do you read the current URL in a Next.js Client Component (usePathname, useSearchParams, useParams)?

Accepted Answer

**Target Audience:** Beginners preparing for Next.js interviews — assumes basic React hooks and the idea of Server vs Client Components.
**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 lab builds, `curl` and a real Chromium browser.

## 1. Why This Even Matters — A Story First

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

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 7

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.

##

Question 8

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 9

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 10

Middleware in Next 15 — what breaks from the 14 upgrade?

Accepted Answer

Next 15 middleware keeps Edge by default but now supports `runtime: 'nodejs'`, async `NextRequest` helpers, and `instrumentation` sharing — update matchers and await `request` APIs.

NEXT.JSDECODED.

Easy

next/font — how does it eliminate layout shift and external requests?

How do metadata files like favicon.ico, icon, opengraph-image and manifest work in Next.js?

What happens when you run next dev, next build and next start?

How do you read the current URL in a Next.js Client Component (usePathname, useSearchParams, useParams)?

Medium

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?

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

What changed for next/image defaults in Next.js 16?

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

Middleware in Next 15 — what breaks from the 14 upgrade?

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?

Hard

What changed about caching defaults in Next.js 15?

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

How do you build a multi-tenant Next.js app with subdomain routing?

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

What is the RSC payload and how does Next.js stream it to the browser?

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

What are the caching layers in Next.js (Request Memoization, Data Cache, Full Route Cache, Router Cache)?

What are intercepting routes in Next.js and what are they used for?