Next.js

export default async function Page(props: PageProps<'/blog/[slug]'>) {
  const { slug } = await props.params;
  const { page = '1' } = await props.searchParams;
  return <Post slug={slug} page={Number(page)} />;
}

import { cacheLife, cacheTag } from 'next/cache';

export async function getProduct(tenantId: string, slug: string) {
  'use cache';
  cacheLife('hours');
  cacheTag(`product:${tenantId}:${slug}`);
  return db.product.findUnique({ where: { tenantId_slug: { tenantId, slug } } });
}

'use server';
import { z } from 'zod';
import { updateTag } from 'next/cache';
import { verifySession } from '@/lib/dal';

const Schema = z.object({ displayName: z.string().min(2).max(50) });
export type State = { errors?: Record<string, string[]>; ok?: boolean };

export async function updateProfile(_prev: State, formData: FormData): Promise<State> {
  const session = await verifySession(); // throws/redirects if not logged in
  const parsed = Schema.safeParse({ displayName: formData.get('displayName') });
  if (!parsed.success) return { errors: parsed.error.flatten().fieldErrors };
  await db.user.update({ where: { id: session.userId }, data: parsed.data });
  updateTag(`user:${session.userId}`);
  return { ok: true };
}

// app/page.tsx (Server Component)
import Modal from './modal'; // 'use client'
import Cart from './cart';   // Server Component, reads DB
export default function Page() {
  return <Modal><Cart /></Modal>;
}

export default async function Page(props: PageProps<'/users/[id]'>) {
  const { id } = await props.params;
  const user = await getUser(id);          // 600 ms
  const orders = await getOrders(id);      // 600 ms
  const recommendations = await getRecs(id); // 600 ms
  return <Dashboard user={user} orders={orders} recs={recommendations} />;
}

// app/admin/page.tsx
import { auth } from '@/lib/auth';
import { redirect } from 'next/navigation';
import { deleteAllRecords } from './actions';

export default async function AdminPage() {
  const session = await auth();
  if (!session?.user?.isAdmin) redirect('/login');
  return (
    <form action={deleteAllRecords}>
      <button>Delete all</button>
    </form>
  );
}

// app/admin/actions.ts
'use server';
export async function deleteAllRecords() {
  await db.record.deleteMany();
}

// app/profile/[slug]/page.tsx
export default async function Page(props: PageProps<'/profile/[slug]'>) {
  const { slug } = await props.params;
  const user = await db.user.findUnique({ where: { slug } }); // full row
  return <ProfileCard user={user} />; // 'use client' component
}

import { cookies } from 'next/headers';

async function getTenant() {
  const tenantId = (await cookies()).get('tenant')?.value;
  return db.tenant.findUnique({ where: { id: tenantId } });
}

export async function TenantBanner() {
  'use cache';
  const tenant = await getTenant();
  return <Banner name={tenant?.name} />;
}

'use server';
import { redirect } from 'next/navigation';

export async function createOrder(_: State, formData: FormData): Promise<State> {
  try {
    const order = await orders.create(parse(formData));
    revalidatePath('/orders');
    redirect(`/orders/${order.id}`);
  } catch (err) {
    return { error: String(err) };
  }
}

export default function Layout({ children, params }: LayoutProps<'/shop/[slug]'>) {
  return (
    <div>
      <Sidebar />{/* static / cached */}
      <Suspense fallback={<h1>Loading…</h1>}>
        {params.then(({ slug }) => <ShopHeading slug={slug} />)}
      </Suspense>
      <Suspense fallback={<AvatarSkeleton />}><UserMenu /></Suspense>
      {children}
    </div>
  );
}

// lib/config.ts
export const API_URL = process.env.NEXT_PUBLIC_API_URL!;
export const NEW_CHECKOUT = process.env.FEATURE_NEW_CHECKOUT === 'true';

// app/checkout/page.tsx (prerendered at build)
import { NEW_CHECKOUT } from '@/lib/config';
export default function Page() {
  return NEW_CHECKOUT ? <NewCheckout /> : <OldCheckout />;
}