App Router File Conventions

app/ ├── layout.tsx # Root layout (required) ├── page.tsx # Home page (/) ├── loading.tsx # Loading UI (Suspense) ├── error.tsx # Error boundary ├── not-found.tsx # 404 page ├── (auth)/ # Route group (no URL impact) │ ├── login/page.tsx # /login │ └── signup/page.tsx # /signup ├── api/ │ └── route.ts # API handler └── _components/ # Private folder (not routed)

Server Components (Default)

// No directive needed - async by default export default async function Page() { const data = await db.query(); return <Component data={data} />; }

Server Actions

// app/actions.ts "use server";

import { revalidatePath } from "next/cache"; import { redirect } from "next/navigation";

export async function createUser(formData: FormData) { const name = formData.get("name") as string;

await db.users.create({ data: { name } });

revalidatePath("/users"); redirect("/users"); }

// Usage <form action={createUser}> <input name="name" required /> <button type="submit">Create</button> </form>

Data Fetching

// Parallel async function Page() { const [users, posts] = await Promise.all([ getUsers(), getPosts(), ]); return <Dashboard users={users} posts={posts} />; }

// Streaming with Suspense <Suspense fallback={<Loading />}> <SlowComponent /> </Suspense>

Route Handlers (API)

// app/api/users/route.ts import { NextRequest, NextResponse } from "next/server";

export async function GET(request: NextRequest) { const users = await db.users.findMany(); return NextResponse.json(users); }

export async function POST(request: NextRequest) { const body = await request.json(); const user = await db.users.create({ data: body }); return NextResponse.json(user, { status: 201 }); }

Middleware

// middleware.ts (root level) import { NextResponse } from "next/server"; import type { NextRequest } from "next/server";

export function middleware(request: NextRequest) { const token = request.cookies.get("token");

if (!token && request.nextUrl.pathname.startsWith("/dashboard")) { return NextResponse.redirect(new URL("/login", request.url)); }

return NextResponse.next(); }

export const config = { matcher: ["/dashboard/:path*"], };

Metadata

// Static export const metadata = { title: "My App", description: "Description", };

// Dynamic export async function generateMetadata({ params }) { const product = await getProduct(params.id); return { title: product.name }; }

server-only Package

import "server-only";

// This will error if imported in client component export async function getSecretData() { return db.secrets.findMany(); }