harshahosur81 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 (
<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
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