Next.js App Router Explained

# Next.js App Router Explained The App Router, introduced as the default in recent Next.js versions, changed how routing and rendering work compared to the older Pages Router. Understanding the difference matters if you're reading tutorials from both eras. ## File Conventions Instead of one file per route, the App Router uses special files inside folders: `page.tsx` for the route UI, `layout.tsx` for shared wrappers, `loading.tsx` for loading states, and `error.tsx` for error boundaries — all scoped to that folder. ## Nested Layouts Layouts persist across navigation within their segment, so a dashboard layout with a sidebar won't re-render every time you switch between dashboard pages. This was awkward to achieve in the Pages Router. ## Server Components by Default Every component inside `app` is a Server Component unless marked with `"use client"`. This shifts more rendering work to the server and reduces the JavaScript bundle sent to users. ## Route Groups and Parallel Routes Folders wrapped in parentheses, like `(marketing)`, organize routes without affecting the URL. Parallel routes let you render multiple independent pages in the same layout — useful for things like modals that also work as full pages. ## Migrating from Pages Router Migration is usually incremental — both routers can coexist during a transition, though most new projects should start directly with the App Router. ## Conclusion The App Router takes a bit of adjustment but gives far more control over layouts, loading states, and rendering boundaries. It's the standard approach taught in MasterPath's Full Stack Development program.