nextjs-upgrade-assistant

Update dependencies with npm install next@16 react@latest react-dom@latest, then run npx @next/codemod upgrade for automated transformations. Follow the phased process: update configuration, migrate code, test builds, and deploy to staging before production.

Next.js 16 removes getStaticProps, getServerSideProps, and getInitialProps in favor of Server Components, and drops the pages/ directory for new apps. Server Components are now default, fetch caching defaults changed, and dynamic routes require explicit generateStaticParams.

Hydration mismatches occur when server and client render different content, such as rendering new Date() directly. Fix this by moving dynamic values into a client component with useEffect and useState, and add suppressHydrationWarning where appropriate.

Clear the .next cache directory, delete node_modules and package-lock.json, reinstall dependencies, and rebuild. Most module-not-found and type errors after upgrades come from stale caches or mismatched dependency versions.

Server Actions require the 'use server' directive at the top of the file and must return only serializable data. Returning objects like Date instances fails; convert them to strings with toISOString() before returning.

Revert using git reset --hard HEAD~1 or git checkout to the previous commit, then delete node_modules and package-lock.json and reinstall dependencies. Verify the rollback by running the dev server and test suite.