Next.js ⚡ Recently updatedUpdated on Jun 30, 2026 — this content may still be evolving.

Next.js: Topics Not to Miss

Check off each topic before your interview.

Core Concepts

• What Next.js adds to React (routing, rendering, optimizations)
• File-based routing
• App Router vs Pages Router
• Server Components vs Client Components ('use client')
• Layouts and nested layouts
• Loading UI (loading.tsx) and error boundaries (error.tsx)

Rendering Strategies

• CSR — client-side rendering
• SSR — server-side rendering per request
• SSG — static generation at build time
• ISR — incremental static regeneration
• When to use each (see rendering-patterns.md)

Data Fetching

• Async Server Components (App Router)
• fetch with caching options (cache, next.revalidate)
• getServerSideProps / getStaticProps (Pages Router)
• Client-side fetch with useEffect or SWR/React Query
• Server Actions (awareness)

Routing

• Dynamic routes [id]
• Catch-all [...slug]
• Route groups (folder) — don’t affect URL
• Link component vs <a>
• useRouter, useParams, useSearchParams
• Middleware (middleware.ts) for auth redirects

API Routes

• Route Handlers (app/api/.../route.ts)
• API routes in Pages Router (pages/api/)
• When API routes vs separate Express backend

Performance & SEO

• next/image — optimization, lazy loading
• next/font — font optimization
• Metadata API (export const metadata)
• Hydration concept

Deployment

• Vercel deployment flow
• Environment variables in Next.js
• Build output (next build)

Authentication Patterns

• Middleware auth check
• NextAuth.js / Auth.js awareness
• Protecting routes server-side vs client-side

Styling

• CSS Modules, Tailwind, styled-components — know what your project uses
• Global CSS in App Router (app/globals.css)

Self-test: For each route in your project, can you say SSR/SSG/CSR and defend the choice?