Nextjs App Router Fundamentals

Migrating from Pages Router to App Router can be tricky, and this guide walks you through it systematically. It covers the full spectrum from understanding file conventions (layout.tsx, page.tsx, loading.tsx) to actually moving your routes and metadata over. The TypeScript guidance is strong, especially the hard rule against using `any` types since it'll break your build. I appreciate the side-by-side comparisons showing old Pages Router structure versus new App Router patterns. The migration steps are concrete: create root layout, move pages to the app directory, update navigation, clean up the old pages folder. It also covers metadata handling, nested layouts, and common routing patterns like dynamic routes and route groups.