nextjs-app-router-expert

Migrating a Next.js Pages Router project involves adopting React Server Components, mapping routes to the new file conventions, and resolving hydration mismatches. You progressively replace data fetching patterns to minimize waterfalls while preserving SEO and predictable runtime behavior.

Hydration mismatches in Next.js App Router occur when server-rendered HTML differs from client-rendered output due to incorrect server/client boundaries. You resolve them by properly configuring Suspense streaming and validating server component data fetching logic.

The best way to handle data fetching and caching is using ISR, on-demand revalidation, and tag-based invalidation. Colocating data fetching within React Server Components minimizes request waterfalls and optimizes application render speed.

Yes, you can use Server Actions for form mutations in Next.js 14 and 15. Server Actions enable form submissions and data mutations directly, supporting optimistic updates to provide a responsive user experience without writing separate API endpoints.

Next.js App Router handles parallel and intercepting routes through file-based routing conventions. This mechanism allows you to render multiple pages simultaneously and intercept navigation to display modals or dynamic UI patterns without unmounting the background context.

Next.js App Router supports middleware and edge deployments for running code closer to users. You can configure middleware for authentication, redirects, geolocation, and A/B testing, then deploy across Node and edge environments like Vercel.