armanzeroeight App Router Helper
Implement Next.js App Router patterns for modern React applications.
Quick Start
App Router (Next.js 13+) uses file-system routing in the app/ directory with Server Components by default.
Key concepts:
- Server Components (default): Render on server, reduce bundle size
- Client Components ('use client'): Interactive, use hooks
- Layouts: Shared UI across routes
- Loading/Error: Automatic UI states
Instructions
Step 1: Understand File Structure
Basic structure:
app/
├── layout.tsx # Root layout (required)
├── page.tsx # Home page (/)
├── loading.tsx # Loading UI
├── error.tsx # Error UI
├── not-found.tsx # 404 page
└── about/
└── page.tsx # About page (/about)
Special files:
layout.tsx: Shared UI, doesn't re-renderpage.tsx: Unique UI for routeloading.tsx: Loading state (Suspense boundary)error.tsx: Error boundarytemplate.tsx: Re-renders on navigationroute.ts: API endpoint
Step 2: Create Layouts
Root layout (required):
// app/layout.tsx
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en">
<body>
<Header />
{children}
<Footer />
</body>
</html>
);
}
Nested layouts:
// app/dashboard/layout.tsx
export default function DashboardLayout({
children,
}: {
children: React.ReactNode
}) {
return (
<div>
<Sidebar />
<main>{children}</main>
</div>
);
}
Layouts persist across navigation and don't re-render.
Step 3: Server vs Client Components
Server Component (default):
// app/products/page.tsx
// No 'use client' = Server Component
async function ProductsPage() {
// Can fetch data directly
const products = await db.products.findMany();
return (
<div>
{products.map(p => (
<ProductCard key={p.id} product={p} />
))}
</div>
);
}
export default ProductsPage;
Client Component:
// app/components/AddToCart.tsx
'use client';
import { useState } from 'react';
export function AddToCart({ productId }: { productId: string }) {
const [count, setCount] = useState(1);
const handleAdd = () => {
// Client-side logic
addToCart(productId, count);
};
return (
<div>
<button => setCount(count - 1)}>-</button>
<span>{count}</span>
<button => setCount(count + 1)}>+</button>
<button to Cart</button>
</div>
);
}
When to use 'use client':
- Event handlers (onClick, onChange)
- React hooks (useState, useEffect, useContext)
- Browser APIs (localStorage, window)
- Third-party libraries requiring client
Step 4: Implement Data Fetching
Server Component data fetching:
// app/posts/page.tsx
async function PostsPage() {
// Fetch in Server Component
const posts = await fetch('https://api.example.com/posts', {
next: { revalidate: 3600 } // Cache for 1 hour
}).then(res => res.json());
return <PostList posts={posts} />;
}
Parallel data fetching:
async function Page() {
// Fetch in parallel
const [user, posts] = await Promise.all([
fetchUser(),
fetchPosts(),
]);
return (
<div>
<UserProfile user={user} />
<PostList posts={posts} />
</div>
);
}
Sequential data fetching:
async function Page() {
const user = await fetchUser();
const posts = await fetchUserPosts(user.id); // Depends on user
return <div>...</div>;
}
Step 5: Organize Routes
Route groups (don't affect URL):
app/
├── (marketing)/
│ ├── layout.tsx # Marketing layout
│ ├── about/
│ │ └── page.tsx # /about
│ └── contact/
│ └── page.tsx # /contact
└── (shop)/
├── layout.tsx # Shop layout
└── products/
└── page.tsx # /products
Dynamic routes:
app/
└── products/
└── [id]/
└── page.tsx # /products/123
// app/products/[id]/page.tsx
export default function ProductPage({
params,
}: {
params: { id: string }
}) {
return <div>Product {params.id}</div>;
}
Catch-all routes:
app/
└── docs/
└── [...slug]/
└── page.tsx # /docs/a, /docs/a/b, /docs/a/b/c
Step 6: Handle Loading and Errors
Loading UI:
// app/dashboard/loading.tsx
export default function Loading() {
return <div>Loading dashboard...</div>;
}
Error handling:
// app/dashboard/error.tsx
'use client'; // Error components must be Client Components
export default function Error({
error,
reset,
}: {
error: Error;
reset: () => void;
}) {
return (
<div>
<h2>Something went wrong!</h2>
<button again</button>
</div>
);
}
Not found:
// app/not-found.tsx
export default function NotFound() {
return <div>404 - Page Not Found</div>;
}
Common Patterns
Streaming with Suspense
import { Suspense } from 'react';
export default function Page() {
return (
<div>
<h1>Dashboard</h1>
<Suspense fallback={<Skeleton />}>
<SlowComponent />
</Suspense>
<FastComponent />
</div>
);
}
Parallel Routes
app/
└── dashboard/
├── layout.tsx
├── @analytics/
│ └── page.tsx
├── @team/
│ └── page.tsx
└── page.tsx
// app/dashboard/layout.tsx
export default function Layout({
children,
analytics,
team,
}: {
children: React.ReactNode;
analytics: React.ReactNode;
team: React.ReactNode;
}) {
return (
<div>
{children}
<div className="grid">
{analytics}
{team}
</div>
</div>
);
}
Intercepting Routes
app/
└── photos/
├── [id]/
│ └── page.tsx
└── (.)[id]/
└── page.tsx # Intercepts /photos/[id]
Metadata
// app/products/[id]/page.tsx
import { Metadata } from 'next';
export async function generateMetadata({
params,
}: {
params: { id: string }
}): Promise<Metadata> {
const product = await fetchProduct(params.id);
return {
title: product.name,
description: product.description,
openGraph: {
images: [product.image],
},
};
}
API Routes
// app/api/products/route.ts
import { NextResponse } from 'next/server';
export async function GET(request: Request) {
const products = await db.products.findMany();
return NextResponse.json(products);
}
export async function POST(request: Request) {
const body = await request.json();
const product = await db.products.create({ data: body });
return NextResponse.json(product, { status: 201 });
}
Dynamic API routes:
// app/api/products/[id]/route.ts
export async function GET(
request: Request,
{ params }: { params: { id: string } }
) {
const product = await db.products.findUnique({
where: { id: params.id }
});
return NextResponse.json(product);
}
Advanced
For detailed patterns:
- Server Components - Deep dive into Server Components
- Client Components - Client Component patterns
- Data Fetching - Advanced data fetching strategies
Troubleshooting
"use client" not working:
- Must be at top of file
- Check for Server Component imports
- Verify no async in Client Components
Data not updating:
- Check cache configuration
- Use revalidatePath or revalidateTag
- Verify fetch cache settings
Layout not applying:
- Ensure layout.tsx exists
- Check file naming (must be exact)
- Verify export default
Hydration errors:
- Server and client HTML must match
- Avoid using browser APIs in Server Components
- Check for dynamic content (dates, random)
Best Practices
- Default to Server Components: Only use 'use client' when needed
- Fetch data where needed: Co-locate data fetching with components
- Use layouts: Share UI and avoid re-renders
- Implement loading states: Use loading.tsx and Suspense
- Handle errors: Add error.tsx boundaries
- Optimize metadata: Use generateMetadata for SEO
- Stream content: Use Suspense for better UX
- Type everything: Use TypeScript for params and props