Next.js App Router Patterns
Comprehensive patterns for Next.js 14+ App Router architecture, Server Components, and modern full-stack React development.
When to Use This Skill Building new Next.js applications with App Router Migrating from Pages Router to App Router Implementing Server Components and streaming Setting up parallel and intercepting routes Optimizing data fetching and caching Building full-stack features with Server Actions Core Concepts 1. Rendering Modes Mode Where When to Use Server Components Server only Data fetching, heavy computation, secrets Client Components Browser Interactivity, hooks, browser APIs Static Build time Content that rarely changes Dynamic Request time Personalized or real-time data Streaming Progressive Large pages, slow data sources 2. File Conventions app/ ├── layout.tsx # Shared UI wrapper ├── page.tsx # Route UI ├── loading.tsx # Loading UI (Suspense) ├── error.tsx # Error boundary ├── not-found.tsx # 404 UI ├── route.ts # API endpoint ├── template.tsx # Re-mounted layout ├── default.tsx # Parallel route fallback └── opengraph-image.tsx # OG image generation
Quick Start // app/layout.tsx import { Inter } from 'next/font/google' import { Providers } from './providers'
const inter = Inter({ subsets: ['latin'] })
export const metadata = { title: { default: 'My App', template: '%s | My App' }, description: 'Built with Next.js App Router', }
export default function RootLayout({ children, }: { children: React.ReactNode }) { return (
// app/page.tsx - Server Component by default async function getProducts() { const res = await fetch('https://api.example.com/products', { next: { revalidate: 3600 }, // ISR: revalidate every hour }) return res.json() }
export default async function HomePage() { const products = await getProducts()
return (
Products
Patterns Pattern 1: Server Components with Data Fetching // app/products/page.tsx import { Suspense } from 'react' import { ProductList, ProductListSkeleton } from '@/components/products' import { FilterSidebar } from '@/components/filters'
interface SearchParams { category?: string sort?: 'price' | 'name' | 'date' page?: string }
export default async function ProductsPage({
searchParams,
}: {
searchParams: Promise
return (
// components/products/ProductList.tsx - Server Component
async function getProducts(filters: ProductFilters) {
const res = await fetch(
${process.env.API_URL}/products?${new URLSearchParams(filters)},
{ next: { tags: ['products'] } }
)
if (!res.ok) throw new Error('Failed to fetch products')
return res.json()
}
export async function ProductList({ category, sort, page }: ProductFilters) { const { products, totalPages } = await getProducts({ category, sort, page })
return (
Pattern 2: Client Components with 'use client' // components/products/AddToCartButton.tsx 'use client'
import { useState, useTransition } from 'react' import { addToCart } from '@/app/actions/cart'
export function AddToCartButton({ productId }: { productId: string }) {
const [isPending, startTransition] = useTransition()
const [error, setError] = useState
const handleClick = () => { setError(null) startTransition(async () => { const result = await addToCart(productId) if (result.error) { setError(result.error) } }) }
return (
{error}
}Pattern 3: Server Actions // app/actions/cart.ts "use server";
import { revalidateTag } from "next/cache"; import { cookies } from "next/headers"; import { redirect } from "next/navigation";
export async function addToCart(productId: string) { const cookieStore = await cookies(); const sessionId = cookieStore.get("session")?.value;
if (!sessionId) { redirect("/login"); }
try { await db.cart.upsert({ where: { sessionId_productId: { sessionId, productId } }, update: { quantity: { increment: 1 } }, create: { sessionId, productId, quantity: 1 }, });
revalidateTag("cart");
return { success: true };
} catch (error) { return { error: "Failed to add item to cart" }; } }
export async function checkout(formData: FormData) { const address = formData.get("address") as string; const payment = formData.get("payment") as string;
// Validate if (!address || !payment) { return { error: "Missing required fields" }; }
// Process order const order = await processOrder({ address, payment });
// Redirect to confirmation
redirect(/orders/${order.id}/confirmation);
}
Pattern 4: Parallel Routes // app/dashboard/layout.tsx export default function DashboardLayout({ children, analytics, team, }: { children: React.ReactNode analytics: React.ReactNode team: React.ReactNode }) { return (
// app/dashboard/@analytics/page.tsx
export default async function AnalyticsSlot() {
const stats = await getAnalytics()
return
// app/dashboard/@analytics/loading.tsx
export default function AnalyticsLoading() {
return
// app/dashboard/@team/page.tsx
export default async function TeamSlot() {
const members = await getTeamMembers()
return
Pattern 5: Intercepting Routes (Modal Pattern) // File structure for photo modal // app/ // ├── @modal/ // │ ├── (.)photos/[id]/page.tsx # Intercept // │ └── default.tsx // ├── photos/ // │ └── [id]/page.tsx # Full page // └── layout.tsx
// app/@modal/(.)photos/[id]/page.tsx import { Modal } from '@/components/Modal' import { PhotoDetail } from '@/components/PhotoDetail'
export default async function PhotoModal({ params, }: { params: Promise<{ id: string }> }) { const { id } = await params const photo = await getPhoto(id)
return (
// app/photos/[id]/page.tsx - Full page version export default async function PhotoPage({ params, }: { params: Promise<{ id: string }> }) { const { id } = await params const photo = await getPhoto(id)
return (
// app/layout.tsx export default function RootLayout({ children, modal, }: { children: React.ReactNode modal: React.ReactNode }) { return (
{children} {modal} ) }Pattern 6: Streaming with Suspense // app/product/[id]/page.tsx import { Suspense } from 'react'
export default async function ProductPage({ params, }: { params: Promise<{ id: string }> }) { const { id } = await params
// This data loads first (blocking) const product = await getProduct(id)
return (
{/* Stream in reviews */}
<Suspense fallback={<ReviewsSkeleton />}>
<Reviews productId={id} />
</Suspense>
{/* Stream in recommendations */}
<Suspense fallback={<RecommendationsSkeleton />}>
<Recommendations productId={id} />
</Suspense>
</div>
) }
// These components fetch their own data
async function Reviews({ productId }: { productId: string }) {
const reviews = await getReviews(productId) // Slow API
return
async function Recommendations({ productId }: { productId: string }) {
const products = await getRecommendations(productId) // ML-based, slow
return
Pattern 7: Route Handlers (API Routes) // app/api/products/route.ts import { NextRequest, NextResponse } from "next/server";
export async function GET(request: NextRequest) { const searchParams = request.nextUrl.searchParams; const category = searchParams.get("category");
const products = await db.product.findMany({ where: category ? { category } : undefined, take: 20, });
return NextResponse.json(products); }
export async function POST(request: NextRequest) { const body = await request.json();
const product = await db.product.create({ data: body, });
return NextResponse.json(product, { status: 201 }); }
// app/api/products/[id]/route.ts export async function GET( request: NextRequest, { params }: { params: Promise<{ id: string }> }, ) { const { id } = await params; const product = await db.product.findUnique({ where: { id } });
if (!product) { return NextResponse.json({ error: "Product not found" }, { status: 404 }); }
return NextResponse.json(product); }
Pattern 8: Metadata and SEO // app/products/[slug]/page.tsx import { Metadata } from 'next' import { notFound } from 'next/navigation'
type Props = { params: Promise<{ slug: string }> }
export async function generateMetadata({ params }: Props): Promise
if (!product) return {}
return { title: product.name, description: product.description, openGraph: { title: product.name, description: product.description, images: [{ url: product.image, width: 1200, height: 630 }], }, twitter: { card: 'summary_large_image', title: product.name, description: product.description, images: [product.image], }, } }
export async function generateStaticParams() { const products = await db.product.findMany({ select: { slug: true } }) return products.map((p) => ({ slug: p.slug })) }
export default async function ProductPage({ params }: Props) { const { slug } = await params const product = await getProduct(slug)
if (!product) notFound()
return
Caching Strategies Data Cache // No cache (always fresh) fetch(url, { cache: "no-store" });
// Cache forever (static) fetch(url, { cache: "force-cache" });
// ISR - revalidate after 60 seconds fetch(url, { next: { revalidate: 60 } });
// Tag-based invalidation fetch(url, { next: { tags: ["products"] } });
// Invalidate via Server Action ("use server"); import { revalidateTag, revalidatePath } from "next/cache";
export async function updateProduct(id: string, data: ProductData) { await db.product.update({ where: { id }, data }); revalidateTag("products"); revalidatePath("/products"); }
Best Practices Do's Start with Server Components - Add 'use client' only when needed Colocate data fetching - Fetch data where it's used Use Suspense boundaries - Enable streaming for slow data Leverage parallel routes - Independent loading states Use Server Actions - For mutations with progressive enhancement Don'ts Don't pass serializable data - Server → Client boundary limitations Don't use hooks in Server Components - No useState, useEffect Don't fetch in Client Components - Use Server Components or React Query Don't over-nest layouts - Each layout adds to the component tree Don't ignore loading states - Always provide loading.tsx or Suspense Resources Next.js App Router Documentation Server Components RFC Vercel Templates
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