nextjs

Next.js 15 defaults to server components for optimal data fetching and rendering. Mark interactive components with 'use client' to establish client component boundaries. Server components handle data fetching and database queries directly, while client components manage state and user interactions, reducing JavaScript sent to the browser.

Server actions are secure functions marked with 'use server' that handle form submissions and mutations. They run only on the server, validate input automatically, perform database updates, and return results to the client without exposing backend logic. Use them to create handlers for photo uploads, gallery creation, and other mutations.

Next.js 15 provides explicit caching controls through fetch options and revalidatePath/revalidateTag functions. Cache server component data using fetch revalidation settings, revalidate on-demand with server actions, and use cache tags for granular invalidation. This optimizes performance while keeping data fresh.

In Next.js 15, cookies, headers, and route params are async APIs that must be awaited in server components. Use 'await cookies()' and 'await headers()' to access request metadata, and 'await params' to read dynamic route segments. This ensures proper hydration and prevents hydration mismatches.

Yes. API routes handle traditional REST endpoints for external consumers or complex workflows, while server actions handle form submissions and client-to-server mutations. Both work in the app router; choose API routes for public endpoints and server actions for internal form handling.

Next.js 15 middleware runs on every request before routing, enabling authentication, redirects, request logging, and header manipulation. Define middleware.ts in your project root to intercept requests, validate sessions, and modify responses. Middleware executes server-side before page rendering.