Next.js App Router: The Complete Guide for 2026

Next.js App Router is the standard for building production React applications in 2026. It introduces server components, streaming SSR, and a file-based routing system that dramatically improves performance.

Server Components vs Client Components

Server components render on the server and send zero JavaScript to the client. Use the 'use client' directive only when you need interactivity.

Layouts and Templates

Nested layouts persist state across navigations. Use layout.tsx for shared UI and template.tsx when you need fresh instances.

Data Fetching Patterns

async function ProductPage({ params }: { params: { id: string } }) {
  const product = await db.product.findUnique({ where: { id: params.id } });
  return <ProductDetails product={product} />;
}

Server Actions

Server actions replace API routes for mutations. They're type-safe and work with progressive enhancement.

Middleware and Edge Runtime

Use middleware for authentication, redirects, and A/B testing at the edge.

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