nextjs

Replace getServerSideProps and getStaticProps with async Server Components and generateStaticParams, move pages/ files into the app/ directory using layout.tsx and page.tsx conventions, and swap next/router imports for next/navigation hooks like useRouter and usePathname.

cookies(), headers(), params, and searchParams are asynchronous in Next.js 16. You must await them, for example const cookieStore = await cookies(), otherwise you get a build or runtime error in Server Components and Route Handlers.

middleware.ts is renamed to proxy.ts in Next.js 16 and runs exclusively on the Node.js runtime. Place proxy.ts at the project root or inside src/ alongside app/, and export a proxy function that rewrites, redirects, or modifies headers.

Add 'use cache' at the top of a component or function, then configure duration with cacheLife() and invalidation tags with cacheTag(). Variants include 'use cache: remote' for cross-deployment caching and 'use cache: private' for per-user data.

Next.js 16 requires a cacheLife profile as the second argument, such as revalidateTag(tag, 'max'), for stale-while-revalidate behavior. For immediate expiration inside Server Actions, use updateTag(tag) instead.

Use Server Actions ('use server' functions) for form submissions and in-app mutations with revalidatePath or revalidateTag. Use Route Handlers (route.ts) for public APIs, webhooks, large file uploads, and streaming responses consumed by external clients.