Next.js App Router — layouts, loading states, parallel routes, and server actions for full-stack React.
Five passes over the same idea, each from a different angle. Do them in order, or jump to whichever you need.
The App Router (Next.js 13+) uses file-system routing with layouts, loading.tsx, error.tsx, and template.tsx conventions. It natively supports React Server Components, streaming, parallel routes, intercepting routes, and Server Actions for mutations. Route groups organize code without affecting URLs.
