Next.js App Router vs Pages Router

Introduction

Next.js offers two distinct routing systems: the original Pages Router and the newer App Router. Understanding their differences is crucial for choosing the right architecture for your project. Since its introduction in Next.js 13, the App Router has become the recommended approach for new applications due to its modern features and performance benefits.

Key Differences

1. Routing Paradigm

• Pages Router:
  • Uses direct file mapping (pages/about.js → /about)
  • Simple convention but limited nesting capabilities
• App Router:
  • Uses folder-based routing (app/about/page.js → /about)
  • Supports nested layouts and shared UI segments
  • Routes defined through folder structure rather than files

2. Component Model

• Pages Router:

  • All components are client components by default
  • Requires custom solutions for shared layouts

  // Traditional layout pattern in pages router
  export default function Layout({ children }) {
    return (
      <div>
        <Navbar />
        {children}
      </div>
    )
  }

• App Router:

  • Uses Server Components by default for better performance
  • Built-in layout support with automatic nesting
  • Special files for common functionality:
    • layout.js: Shared UI between segments
    • loading.js: Automatic loading states
    • error.js: Error boundaries

3. Data Fetching Methods

Method	Pages Router	App Router
Data Fetching	getServerSideProps	Server Components + fetch
	getStaticProps	with caching options
	getInitialProps
API Calls	Client-side fetch/axios	Server Actions + Route Handlers

4. Rendering Performance

• App Router:
  • Supports streaming for progressive content loading
  • Partial rendering through React Suspense
  • Reduced bundle size due to server components
• Pages Router:
  • Full page rendering per route
  • Limited partial rendering capabilities

├── pages/                 ├── app/
│   ├── index.js           │   ├── layout.js
│   ├── about.js           │   ├── page.js        # /
│   └── products/          │   ├── about/
│       ├── index.js       │   │   └── page.js    # /about
│       └── [id].js        │   └── products/
│                          │       ├── page.js    # /products
│                          │       └── [id]/
│                          │           └── page.js # /products/:id

Performance and Optimization

• Server Components: App Router executes components on the server by default, reducing JavaScript sent to clients
• Caching: Built-in fetch caching in App Router simplifies performance optimization
• Partial Rendering: App Router updates only modified UI sections during navigation
• Streaming: App Router progressively streams UI chunks for faster perceived performance

SEO Advantage

App Router provides improved SEO capabilities through automatic server rendering without additional configuration

When to Use Each Router

Use App Router When:

• Starting a new project (Next.js official recommendation)
• Building complex layouts requiring nested routes
• Need server actions for data mutations
• Require streaming or React Suspense
• Prioritizing component-based state management
• Want built-in loading/error states

Use Pages Router When:

• Maintaining legacy Next.js applications
• Migrating incrementally from Pages to App Router
• Building simple prototypes without advanced features
• Relying on Next.js plugins not yet compatible with App Router
• Working with extensive existing getServerSideProps logic

Migration Considerations

1. Both routers can coexist in the same project when incrementally migrating
2. App Router takes precedence over Pages Router
3. Partial migration should start from leaf routes first
4. Official migration guide: Next.js Migrating to App Router

Best Practices

1. For new projects, consistently use App Router and its modern features
2. Convert client components to server components whenever possible
3. Leverage colocated data fetching in Server Components

// App Router server component with data fetching
export default async function ProductPage({ params }) {
  const product = await fetchProductData(params.id); 
  
  return (
    <ProductDetail product={product}>
  )
}

4. For Pages Router projects:
   • Enable static site generation for better performance
   • Abstract layout sharing patterns
   • Consider incremental App Router adoption for SEO-critical pages

Conclusion

App Router represents the future of Next.js development with its server-centric approach, layout system, and performance innovations. While Pages Router remains viable for existing projects and simple use cases, new applications should adopt App Router to leverage features like server components, streaming, and enhanced caching. The choice ultimately depends on your project requirements, but the App Router's performance benefits and modern architecture make it the recommended approach for most applications.