next-best-practices

In Next.js 15+, params and searchParams are Promises that must be awaited. Type them as Promise<{ slug: string }> and await them in pages, layouts, route handlers, and generateMetadata. A codemod (npx @next/codemod@latest next-async-request-api) automates migration.

Use Server Actions for mutations triggered from your UI like form submissions, since they offer type safety and progressive enhancement. Use Route Handlers for external APIs, webhooks, mobile clients, and GET endpoints needing HTTP caching.

Hydration errors occur when server and client HTML differ, commonly from browser APIs like window, dates rendered in different timezones, random values, or invalid HTML nesting. Fix by rendering dynamic values client-side with useEffect or the useId hook.

No, props crossing the server/client boundary must be JSON-serializable, so plain functions are invalid. The exception is Server Actions marked with 'use server', which can be passed to client components. Dates, Maps, and class instances must also be serialized first.

Set output: 'standalone' in next.config.js to produce a minimal server.js with production dependencies, then copy .next/static and public folders into your container. For multi-instance ISR, configure a custom cache handler backed by Redis or S3.

useSearchParams triggers a CSR bailout in static routes unless wrapped in a Suspense boundary. Wrap the component using it in <Suspense> with a fallback so the rest of the page stays statically rendered.