Route Handlers replace API routes in the App Router. They export functions named after HTTP verbs and return Web Standard Response objects.
Common Interview Questions
Q: Basic route handler structure?
Answer: Colocate handlers in route.ts files. Export GET, POST, PUT, PATCH, DELETE as needed.
// app/api/users/route.ts
export async function GET() {
const users = await db.user.findMany();
return Response.json(users);
}
export async function POST(request: Request) {
const body = await request.json();
const user = await db.user.create({ data: body });
return Response.json(user, { status: 201 });
}
Q: Route handlers vs Server Actions?
Answer: Route handlers are HTTP endpoints for any client (mobile, webhooks). Server Actions are RPC-style mutations from React components with built-in progressive enhancement.
Q: Dynamic route segments in APIs?
Answer: In Next.js 15+, params is a Promise and must be awaited in async handlers.
// app/api/posts/[id]/route.ts
export async function GET(_req, { params }) {
const { id } = await params;
return Response.json(await getPost(id));
}
Q: CORS in route handlers?
Answer: Set Access-Control-* headers on Response or use middleware. For public APIs, handle OPTIONS preflight explicitly.
Key Points for Interviews
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route.ts cannot export page default alongside handlers
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Use Web Response/Request APIs
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Validate input and authenticate every mutation
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Edge or Node runtime via export const runtime
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Coexist with legacy pages/api during migration