260223:1415 20260223 nextJS & nestJS Best pratices

.agents/skills/next-best-practices/file-conventions.md

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+# File Conventions
+
+Next.js App Router uses file-based routing with special file conventions.
+
+## Project Structure
+
+Reference: https://nextjs.org/docs/app/getting-started/project-structure
+
+```
+app/
+├── layout.tsx          # Root layout (required)
+├── page.tsx            # Home page (/)
+├── loading.tsx         # Loading UI
+├── error.tsx           # Error UI
+├── not-found.tsx       # 404 UI
+├── global-error.tsx    # Global error UI
+├── route.ts            # API endpoint
+├── template.tsx        # Re-rendered layout
+├── default.tsx         # Parallel route fallback
+├── blog/
+│   ├── page.tsx        # /blog
+│   └── [slug]/
+│       └── page.tsx    # /blog/:slug
+└── (group)/            # Route group (no URL impact)
+    └── page.tsx
+```
+
+## Special Files
+
+| File | Purpose |
+|------|---------|
+| `page.tsx` | UI for a route segment |
+| `layout.tsx` | Shared UI for segment and children |
+| `loading.tsx` | Loading UI (Suspense boundary) |
+| `error.tsx` | Error UI (Error boundary) |
+| `not-found.tsx` | 404 UI |
+| `route.ts` | API endpoint |
+| `template.tsx` | Like layout but re-renders on navigation |
+| `default.tsx` | Fallback for parallel routes |
+
+## Route Segments
+
+```
+app/
+├── blog/               # Static segment: /blog
+├── [slug]/             # Dynamic segment: /:slug
+├── [...slug]/          # Catch-all: /a/b/c
+├── [[...slug]]/        # Optional catch-all: / or /a/b/c
+└── (marketing)/        # Route group (ignored in URL)
+```
+
+## Parallel Routes
+
+```
+app/
+├── @analytics/
+│   └── page.tsx
+├── @sidebar/
+│   └── page.tsx
+└── layout.tsx          # Receives { analytics, sidebar } as props
+```
+
+## Intercepting Routes
+
+```
+app/
+├── feed/
+│   └── page.tsx
+├── @modal/
+│   └── (.)photo/[id]/  # Intercepts /photo/[id] from /feed
+│       └── page.tsx
+└── photo/[id]/
+    └── page.tsx
+```
+
+Conventions:
+- `(.)` - same level
+- `(..)` - one level up
+- `(..)(..)` - two levels up
+- `(...)` - from root
+
+## Private Folders
+
+```
+app/
+├── _components/        # Private folder (not a route)
+│   └── Button.tsx
+└── page.tsx
+```
+
+Prefix with `_` to exclude from routing.
+
+## Middleware / Proxy
+
+### Next.js 14-15: `middleware.ts`
+
+```ts
+// middleware.ts (root of project)
+import { NextResponse } from 'next/server';
+import type { NextRequest } from 'next/server';
+
+export function middleware(request: NextRequest) {
+  // Auth, redirects, rewrites, etc.
+  return NextResponse.next();
+}
+
+export const config = {
+  matcher: ['/dashboard/:path*', '/api/:path*'],
+};
+```
+
+### Next.js 16+: `proxy.ts`
+
+Renamed for clarity - same capabilities, different names:
+
+```ts
+// proxy.ts (root of project)
+import { NextResponse } from 'next/server';
+import type { NextRequest } from 'next/server';
+
+export function proxy(request: NextRequest) {
+  // Same logic as middleware
+  return NextResponse.next();
+}
+
+export const proxyConfig = {
+  matcher: ['/dashboard/:path*', '/api/:path*'],
+};
+```
+
+| Version | File | Export | Config |
+|---------|------|--------|--------|
+| v14-15 | `middleware.ts` | `middleware()` | `config` |
+| v16+ | `proxy.ts` | `proxy()` | `proxyConfig` |
+
+**Migration**: Run `npx @next/codemod@latest upgrade` to auto-rename.
+
+## File Conventions Reference
+
+Reference: https://nextjs.org/docs/app/api-reference/file-conventions