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 environment variables work in Next.js (the NEXT_PUBLIC_ prefix)?

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 3

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 4

How do you run Turbopack locally — `next dev --turbo` vs default?

Accepted Answer

`next dev --turbo` (now default in Next 15) gives sub-100ms HMR via persistent `.next/cache/turbo` — use `--show-config` or `TURBOPACK=1` to debug.

Question 5

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 6

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 7

How do you create a new Next.js app, and what is in the project structure?

Accepted Answer

**Target Audience:** Beginners preparing for Next.js interviews — no prior Next.js knowledge assumed, basic React 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 real run of `create-next-app@16.4.2`, `next build` and `next start` in a lab.

## 1. Why This Even Matters

Question 8

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 9

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 10

Intercepting routes — how do you build an Instagram-style modal?

Accepted Answer

Intercepting routes `(.)`, `(..)`, `(...)` render a route inside the current layout instead of navigating — perfect for modals that become full pages on refresh or direct link.

NEXT.JSDECODED.

Easy

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

How do environment variables work in Next.js (the NEXT_PUBLIC_ prefix)?

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

How do you run Turbopack locally — `next dev --turbo` vs default?

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)?

How do you create a new Next.js app, and what is in the project structure?

Medium

What is the route segment config in Next.js (dynamic, revalidate, runtime)?

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

Intercepting routes — how do you build an Instagram-style modal?

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 do you implement search, filtering and pagination with URL search params in the App Router?

Server Components and external packages — what does `serverComponentsExternalPackages` do?

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

Hard

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

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

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

What are parallel routes (@slot) in Next.js and when would you use them?

What are Multi-Zones in Next.js and when would you split an app into zones?

Parallel routes (@slot) — how do you build a dashboard with independent slots?

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

How do you implement dynamic Open Graph images in Next.js (ImageResponse)?