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Next.js: Revision Sheet

Rendering (MEMORIZE)

Pattern	When	App Router
SSG	Static, build time	`fetch` default cache
SSR	Per request, fresh	`cache: 'no-store'`
ISR	Static + regen	`next: { revalidate: N }`
CSR	Client fetch	`'use client'` + useEffect

Decision Quick Pick

Blog/docs → SSG
Product catalog → ISR
User dashboard → CSR/SSR + auth
Personalized feed → SSR
Landing page → SSG

App Router Structure

app/
  layout.tsx      # wraps all pages
  page.tsx        # route UI
  loading.tsx     # Suspense fallback
  error.tsx       # error boundary
  [id]/page.tsx   # dynamic route
  api/.../route.ts

Server vs Client

Server (default): async fetch, no hooks, smaller bundle
Client: 'use client', useState, onClick

Key APIs

import Link from 'next/link';
import Image from 'next/image';
import { useRouter, useParams, useSearchParams } from 'next/navigation';

Pages Router (legacy)

getStaticProps → SSG
getServerSideProps → SSR
getStaticPaths → dynamic SSG paths

Hydration

Server HTML + client JS attach. Mismatch if server ≠ client render.

Middleware

middleware.ts — auth redirects, headers, geo routing.

Metadata

export const metadata = { title: '...', description: '...' };

Image

next/image — optimized, lazy, requires width/height or fill.

Env Vars

NEXT_PUBLIC_* → browser
Others → server only

Quick Answers

Question	Answer
App vs Pages Router?	App = RSC, layouts; new projects use App
Why ISR?	CDN speed + periodic updates without full rebuild
Link vs a?	Link client-side navigation, prefetch
Route groups?	`(folder)` organizes, not in URL
Server Actions?	Run server code from forms — mutations

Red Flags

SSR everything (expensive)
SSG for personalized pages (wrong data)
'use client' on entire app (defeats RSC)
useEffect fetch what Server Component could do