260223:1415 20260223 nextJS & nestJS Best pratices

.agents/skills/next-best-practices/route-handlers.md

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+# Route Handlers
+
+Create API endpoints with `route.ts` files.
+
+## Basic Usage
+
+```tsx
+// app/api/users/route.ts
+export async function GET() {
+  const users = await getUsers()
+  return Response.json(users)
+}
+
+export async function POST(request: Request) {
+  const body = await request.json()
+  const user = await createUser(body)
+  return Response.json(user, { status: 201 })
+}
+```
+
+## Supported Methods
+
+`GET`, `POST`, `PUT`, `PATCH`, `DELETE`, `HEAD`, `OPTIONS`
+
+## GET Handler Conflicts with page.tsx
+
+**A `route.ts` and `page.tsx` cannot coexist in the same folder.**
+
+```
+app/
+├── api/
+│   └── users/
+│       └── route.ts    # /api/users
+└── users/
+    ├── page.tsx        # /users (page)
+    └── route.ts        # Warning: Conflicts with page.tsx!
+```
+
+If you need both a page and an API at the same path, use different paths:
+
+```
+app/
+├── users/
+│   └── page.tsx        # /users (page)
+└── api/
+    └── users/
+        └── route.ts    # /api/users (API)
+```
+
+## Environment Behavior
+
+Route handlers run in a **Server Component-like environment**:
+
+- Yes: Can use `async/await`
+- Yes: Can access `cookies()`, `headers()`
+- Yes: Can use Node.js APIs
+- No: Cannot use React hooks
+- No: Cannot use React DOM APIs
+- No: Cannot use browser APIs
+
+```tsx
+// Bad: This won't work - no React DOM in route handlers
+import { renderToString } from 'react-dom/server'
+
+export async function GET() {
+  const html = renderToString(<Component />)  // Error!
+  return new Response(html)
+}
+```
+
+## Dynamic Route Handlers
+
+```tsx
+// app/api/users/[id]/route.ts
+export async function GET(
+  request: Request,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const { id } = await params
+  const user = await getUser(id)
+
+  if (!user) {
+    return Response.json({ error: 'Not found' }, { status: 404 })
+  }
+
+  return Response.json(user)
+}
+```
+
+## Request Helpers
+
+```tsx
+export async function GET(request: Request) {
+  // URL and search params
+  const { searchParams } = new URL(request.url)
+  const query = searchParams.get('q')
+
+  // Headers
+  const authHeader = request.headers.get('authorization')
+
+  // Cookies (Next.js helper)
+  const cookieStore = await cookies()
+  const token = cookieStore.get('token')
+
+  return Response.json({ query, token })
+}
+```
+
+## Response Helpers
+
+```tsx
+// JSON response
+return Response.json({ data })
+
+// With status
+return Response.json({ error: 'Not found' }, { status: 404 })
+
+// With headers
+return Response.json(data, {
+  headers: {
+    'Cache-Control': 'max-age=3600',
+  },
+})
+
+// Redirect
+return Response.redirect(new URL('/login', request.url))
+
+// Stream
+return new Response(stream, {
+  headers: { 'Content-Type': 'text/event-stream' },
+})
+```
+
+## When to Use Route Handlers vs Server Actions
+
+| Use Case | Route Handlers | Server Actions |
+|----------|----------------|----------------|
+| Form submissions | No | Yes |
+| Data mutations from UI | No | Yes |
+| Third-party webhooks | Yes | No |
+| External API consumption | Yes | No |
+| Public REST API | Yes | No |
+| File uploads | Both work | Both work |
+
+**Prefer Server Actions** for mutations triggered from your UI.
+**Use Route Handlers** for external integrations and public APIs.