nextjs-15

To structure Next.js 15 App Router projects, define layouts and pages in the app/ directory, using server components by default and client components for interactivity. This separation enforces clear boundaries for data fetching and rendering.

Streaming with Suspense in Next.js is implemented by wrapping dynamic components in Suspense boundaries within app/ layouts or pages. This enables parallel data fetching and progressively renders UI chunks to improve perceived loading performance.

API route handlers in a Next.js 15 app directory are created by defining route.ts files inside the app/api/ folder. These route handlers process incoming HTTP requests and return responses, functioning as backend endpoints within your application structure.

Server actions in Next.js should be used for mutations and form submissions directly within server components, whereas API route handlers are better for external API consumption. Server actions streamline data mutations without creating separate API endpoints.

Configuring middleware for protected routes using Next.js route groups involves defining conditional routing logic in middleware.ts and organizing authenticated sections into folders like (auth)/. This pattern secures specific application areas globally.

Loading and error boundaries are needed in a Next.js App Router project to handle streaming states and unexpected failures gracefully. Using loading.tsx and error.tsx files ensures robust UI fallbacks during data fetching and runtime errors.