SKILL.md
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 generationQuick 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 (
<html lang="en" suppressHydrationWarning>
<body className={inter.className}>
<Providers>{children}</Providers>
</body>
</html>
)
}
// 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 (
<main>
<h1>Products</h1>
<ProductGrid products={products} />
</main>
)
}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<SearchParams>
}) {
const params = await searchParams
return (
<div className="flex gap-8">
<FilterSidebar />
<Suspense
key={JSON.stringify(params)}
fallback={<ProductListSkeleton />}
>
<ProductList
category={params.category}
sort={params.sort}
page={Number(params.page) || 1}
/>
</Suspense>
</div>
)
}
// 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 (
<div>
<div className="grid grid-cols-3 gap-4">
{products.map((product) => (
<ProductCard key={product.id} product={product} />
))}
</div>
<Pagination currentPage={page} totalPages={totalPages} />
</div>
)
}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<string | null>(null)
const handleClick = () => {
setError(null)
startTransition(async () => {
const result = await addToCart(productId)
if (result.error) {
setError(result.error)
}
})
}
return (
<div>
<button
onClick={handleClick}
disabled={isPending}
className="btn-primary"
>
{isPending ? 'Adding...' : 'Add to Cart'}
</button>
{error && <p className="text-red-500 text-sm">{error}</p>}
</div>
)
}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 (
<div className="dashboard-grid">
<main>{children}</main>
<aside className="analytics-panel">{analytics}</aside>
<aside className="team-panel">{team}</aside>
</div>
)
}
// app/dashboard/@analytics/page.tsx
export default async function AnalyticsSlot() {
const stats = await getAnalytics()
return <AnalyticsChart data={stats} />
}
// app/dashboard/@analytics/loading.tsx
export default function AnalyticsLoading() {
return <ChartSkeleton />
}
// app/dashboard/@team/page.tsx
export default async function TeamSlot() {
const members = await getTeamMembers()
return <TeamList members={members} />
}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 (
<Modal>
<PhotoDetail photo={photo} />
</Modal>
)
}
// 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 (
<div className="photo-page">
<PhotoDetail photo={photo} />
<RelatedPhotos photoId={id} />
</div>
)
}
// app/layout.tsx
export default function RootLayout({
children,
modal,
}: {
children: React.ReactNode
modal: React.ReactNode
}) {
return (
<html>
<body>
{children}
{modal}
</body>
</html>
)
}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 (
<div>
{/* Immediate render */}
<ProductHeader product={product} />
{/* 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 <ReviewList reviews={reviews} />
}
async function Recommendations({ productId }: { productId: string }) {
const products = await getRecommendations(productId) // ML-based, slow
return <ProductCarousel products={products} />
}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<Metadata> {
const { slug } = await params
const product = await getProduct(slug)
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 <ProductDetail product={product} />
}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