Complete Guide to Next.js App Router

Next.js 13 introduced the App Router, a new way to handle routing in Next.js applications. Built on top of React Server Components, it offers improved performance and developer experience.

What is App Router?

The App Router is a new paradigm for Next.js applications that leverages React's latest features, including:

- Server Components
- Streaming
- Improved data fetching
- Nested layouts
- Advanced routing patterns

File-based Routing

The App Router uses a file-based routing system where the file structure determines the routes:

`
app/
├── page.tsx // Route: /
├── about/
│ └── page.tsx // Route: /about
└── blog/
├── page.tsx // Route: /blog
└── [slug]/
└── page.tsx // Route: /blog/[slug]
`

Layouts and Templates

Layouts and templates allow you to share UI between multiple pages:

`tsx
// app/layout.tsx
export default function RootLayout({
children,
}: {
children: React.ReactNode;
}) {
return (

{children}



);
}
`

Data Fetching

Server Components make data fetching simpler and more efficient:

`tsx
async function BlogPost({ params }: { params: { slug: string } }) {
const post = await fetch(/api/posts/${params.slug});

return (

{post.title}

{post.content}

);
}
`

Loading and Error States

The App Router provides built-in support for loading and error states:

`tsx
// app/blog/loading.tsx
export default function Loading() {
return

;
}

// app/blog/error.tsx
export default function Error({
error,
reset,
}: {
error: Error;
reset: () => void;
}) {
return (

);
}
`

Conclusion

The App Router represents a significant step forward for Next.js applications. By leveraging React Server Components and providing a more intuitive file-based routing system, it makes building modern web applications easier and more efficient.