Upgrading to Next.js 16 and React 19

Overview

This post covers a full migration path for a production portfolio app, including routing, UI library compatibility, and build system changes.

What Changed

• Next.js moved middleware conventions toward proxy handlers.
• React 19 removed some legacy typings and tightened behavior around render trees.
• MUI v7 changed several layout APIs, requiring updates in grid-heavy views.

Migration Checklist

1. Upgrade dependencies in small groups.
2. Fix type errors first, then runtime warnings.
3. Replace deprecated patterns before optimizing styles.
4. Validate key routes after each deploy.

Results

After migration, the app built cleanly and route startup remained stable with Docker warm-up verification.