Next.js 14+ App Router patterns including RSC, ISR, middleware, parallel routes, and data fetching
app/
layout.tsx # Root layout (wraps all pages)
page.tsx # Home route /
loading.tsx # Route-level Suspense fallback
error.tsx # Route-level error boundary
not-found.tsx # Custom 404
(marketing)/
about/page.tsx # /about (grouped without URL segment)
dashboard/
layout.tsx # Nested layout for /dashboard/*
page.tsx # /dashboard
@analytics/page.tsx # Parallel route slot
@activity/page.tsx # Parallel route slot
settings/
page.tsx # /dashboard/settings
api/
webhooks/route.ts # Route handler (POST /api/webhooks)
Route groups (name) organize code without affecting URLs. Parallel routes @slot render multiple pages simultaneously.
async function ProductPage({ params }: { params: Promise<{ id: string }> }) {
const { id } = await params;
const product = await db.product.findUnique({ where: { id } });
if (!product) notFound();
return (
<div>
<h1>{product.name}</h1>
<p>{product.description}</p>
<Suspense fallback={<ReviewsSkeleton />}>
<Reviews productId={id} />
</Suspense>
</div>
);
}
async function Reviews({ productId }: { productId: string }) {
const reviews = await db.review.findMany({ where: { productId } });
return (
<ul>
{reviews.map(r => <li key={r.id}>{r.text} - {r.rating}/5</li>)}
</ul>
);
}
Server Components are the default. They run on the server, can access databases directly, and send zero JavaScript to the client.
export const revalidate = 3600;
async function BlogPage() {
const posts = await fetch("https://api.example.com/posts", {
next: { revalidate: 3600, tags: ["posts"] },
}).then(r => r.json());
return <PostList posts={posts} />;
}
import { revalidateTag, revalidatePath } from "next/cache";
export async function createPost(formData: FormData) {
"use server";
await db.post.create({ data: { title: formData.get("title") as string } });
revalidateTag("posts");
revalidatePath("/blog");
}
import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";
export function middleware(request: NextRequest) {
const token = request.cookies.get("session")?.value;
if (request.nextUrl.pathname.startsWith("/dashboard") && !token) {
return NextResponse.redirect(new URL("/login", request.url));
}
const response = NextResponse.next();
response.headers.set("x-request-id", crypto.randomUUID());
return response;
}
export const config = {
matcher: ["/dashboard/:path*", "/api/:path*"],
};
Middleware runs at the edge before every matched request. Keep it lightweight.
"use server";
import { z } from "zod";
import { revalidatePath } from "next/cache";
const schema = z.object({
email: z.string().email(),
name: z.string().min(2).max(100),
});
export async function updateProfile(prevState: any, formData: FormData) {
const parsed = schema.safeParse(Object.fromEntries(formData));
if (!parsed.success) {
return { errors: parsed.error.flatten().fieldErrors };
}
await db.user.update({
where: { email: parsed.data.email },
data: { name: parsed.data.name },
});
revalidatePath("/profile");
return { success: true };
}
'use client' to top-level layout or page componentsuseEffect for data fetching instead of Server Components or use()<Suspense>loading.tsx and error.tsx conventions'use client' only on interactive leaves<Suspense> boundaries wrap independent async sectionsloading.tsx and error.tsx exist for key routesrevalidateTag or revalidatePath called after mutations