App Router vs Page Router: A Comprehensive Comparison in Next.js

Next.js has evolved significantly over time, introducing new features and paradigms that improve the developer experience and the performance of web applications. Among the key routing systems in Next.js are the App Router and the Page Router. These routing systems serve as the backbone of Next.js applications, managing how pages and components are rendered and navigated. In this blog post, we will explore each router in detail, covering their features, differences, scenarios in which you might choose one over the other, and provide code examples to demonstrate practical usage.

Introduction to Page Router (Pages Directory)

The Page Router, also known as the Pages Directory Router, is the original routing system in Next.js. It has been used since the inception of Next.js and has become a well-known and effective way to create routes in a Next.js application.

Key Features of Page Router

• File-Based Routing: Pages are created by adding files to the pages/ directory. Each file in this directory automatically becomes a route.
• Automatic Routing: No manual configuration is needed to set up routes. The file structure defines the routes, making it easy to understand and modify.
• Dynamic Routing: The Page Router supports dynamic routing through the use of brackets ([param]), allowing developers to create dynamic URL segments.
• Server-Side Rendering (SSR) and Static Site Generation (SSG): The Page Router provides SSR and SSG out of the box using functions like getServerSideProps and getStaticProps.
• Built-In API Routes: You can create API routes in the pages/api/ directory, which is useful for building backend functionality directly in your Next.js project.

Code Example: Creating a Page in Page Router

To create a simple about page in the Page Router:

// File: pages/about.js
 
export default function About() {
  return (
    <div>
      <h1>About Us</h1>
      <p>Welcome to the About page!</p>
    </div>
  );
}

To create a dynamic route for a blog post:

// File: pages/blog/[id].js
 
import { useRouter } from 'next/router';
 
export default function BlogPost() {
  const router = useRouter();
  const { id } = router.query;
 
  return (
    <div>
      <h1>Blog Post: {id}</h1>
      <p>This is a blog post with ID: {id}</p>
    </div>
  );
}

Advantages of Page Router

• Simplicity: The Page Router is straightforward to use, especially for smaller projects. Developers can simply add a file to the pages/ directory, and it instantly becomes accessible as a route.
• No Extra Configuration Needed: With the file-based system, the routes are generated automatically without any additional configuration.
• Built-In Data Fetching: Functions like getStaticProps, getServerSideProps, and getInitialProps provide convenient ways to fetch data for pages.

Limitations of Page Router

• Limited Layout Flexibility: The Page Router provides less flexibility when it comes to handling multiple layouts or nested layouts compared to the App Router.
• Tightly Coupled Data Fetching: The built-in data fetching methods are page-centric, which can make it difficult to reuse code and data fetching logic across different components.

Introduction to App Router (App Directory)

The App Router is a newer routing system introduced in Next.js to offer more flexible and powerful routing capabilities, making it especially suitable for complex applications that require greater control over rendering and layouts.

Key Features of App Router

• Component-Based Routing: Instead of relying solely on file-based routes, the App Router uses components within the app/ directory to define routes and layout structures.
• Nested Layouts and Shared Layouts: The App Router provides powerful support for nested and shared layouts, making it easy to create consistent layouts across pages or sections of your application.
• Server Components: The App Router supports React Server Components, allowing developers to fetch data on the server and seamlessly render it on the client, improving both performance and developer experience.
• Flexible Data Fetching: Data fetching in the App Router is more flexible compared to the Page Router. You can use server components to manage data fetching, allowing for more granular control over how and where data is fetched.
• Parallel Routing: The App Router supports parallel routing, which allows you to render multiple routes simultaneously within different parts of the UI, making complex navigations more intuitive.

Code Example: Creating a Route in App Router

To create a route using the App Router with a simple layout:

// File: app/about/page.js
 
export default function About() {
  return (
    <div>
      <h1>About Us</h1>
      <p>Welcome to the About page using the App Router!</p>
    </div>
  );
}

To create a nested layout for the dashboard section:

// File: app/dashboard/layout.js
 
export default function DashboardLayout({ children }) {
  return (
    <div>
      <nav>
        <ul>
          <li><a href="/dashboard/overview">Overview</a></li>
          <li><a href="/dashboard/settings">Settings</a></li>
        </ul>
      </nav>
      <main>{children}</main>
    </div>
  );
}

To create a page within the dashboard section:

// File: app/dashboard/overview/page.js
 
export default function Overview() {
  return (
    <div>
      <h1>Dashboard Overview</h1>
      <p>Welcome to your dashboard overview.</p>
    </div>
  );
}

Advantages of App Router

• Improved Layout Management: With nested and shared layouts, managing multiple layouts is simpler and more efficient. You can easily define different layouts for different sections of your app, providing a more modular approach.
• Server Components: The use of server components can greatly reduce the amount of JavaScript sent to the client, resulting in faster load times and improved performance.
• Better Code Reusability: The App Router allows for a more component-driven architecture, improving the ability to reuse logic and components across different parts of the application.

Limitations of App Router

• Steeper Learning Curve: The App Router introduces new concepts, such as server components and parallel routing, which can be challenging for developers who are used to the simplicity of the Page Router.
• More Configuration: Unlike the Page Router, which relies heavily on convention, the App Router requires more explicit configuration, which can add complexity, especially for small projects.

Key Differences Between App Router and Page Router

Rendering Flexibility

Page Router: SSR and SSG

With the Page Router, you can easily implement Server-Side Rendering (SSR) and Static Site Generation (SSG) using the built-in functions like getServerSideProps and getStaticProps. These methods allow developers to determine at build-time or request-time how pages should be rendered.

Code Example: Data Fetching with Page Router

// File: pages/blog/[id].js
 
export async function getStaticProps(context) {
  const { id } = context.params;
  // Fetch data based on the ID
  const postData = await fetch(`https://api.example.com/posts/${id}`).then(res => res.json());
 
  return {
    props: {
      post: postData,
    },
  };
}
 
export async function getStaticPaths() {
  const posts = await fetch('https://api.example.com/posts').then(res => res.json());
  const paths = posts.map(post => ({ params: { id: post.id.toString() } }));
 
  return {
    paths,
    fallback: false,
  };
}
 
export default function BlogPost({ post }) {
  return (
    <div>
      <h1>{post.title}</h1>
      <p>{post.content}</p>
    </div>
  );
}

App Router: Server Components and More

The App Router introduces the concept of Server Components, which allows developers to build components that render on the server by default. This can drastically reduce the JavaScript needed on the client side, resulting in faster page loads and better overall performance. Additionally, with parallel and nested routing, the App Router offers more fine-grained control over how different sections of an application are rendered and navigated.

Code Example: Data Fetching with App Router

// File: app/blog/[id]/page.js
 
export default async function BlogPost({ params }) {
  const { id } = params;
  // Fetch data based on the ID
  const postData = await fetch(`https://api.example.com/posts/${id}`).then(res => res.json());
 
  return (
    <div>
      <h1>{postData.title}</h1>
      <p>{postData.content}</p>
    </div>
  );
}

Routing Complexity

Page Router: Simple and Intuitive

The Page Router’s file-based routing is simple and effective for most use cases. Adding a new route is as easy as adding a new file to the pages/ directory. This approach is ideal for smaller projects or when quick and straightforward routing is required.

App Router: Advanced Capabilities

The App Router is designed for more complex routing needs. It supports parallel routing, which allows multiple parts of the UI to change independently based on the current route. This is particularly useful for applications that require multiple views or panels that update concurrently, such as dashboards or multi-step workflows.

Code Example: Parallel Routing with App Router

// File: app/(marketing)/layout.js
 
export default function MarketingLayout({ children }) {
  return (
    <div>
      <aside>
        <nav>
          <a href="/">Home</a>
          <a href="/about">About</a>
        </nav>
      </aside>
      <main>{children}</main>
    </div>
  );
}
 
// File: app/(dashboard)/page.js
 
export default function DashboardPage() {
  return (
    <div>
      <h1>Dashboard Overview</h1>
      <p>Information specific to the user dashboard.</p>
    </div>
  );
}

When to Use App Router vs Page Router

When to Use Page Router

• Smaller Projects: For smaller projects or prototypes where simplicity is key, the Page Router is an ideal choice.
• Quick Prototyping: If you need to quickly spin up a project with minimal setup, the Page Router’s file-based routing is efficient and easy to use.
• Limited Layout Requirements: If your application does not require complex nested layouts, the Page Router is sufficient.

When to Use App Router

• Complex Layouts: For larger projects that require multiple nested or shared layouts, the App Router is the better choice.
• Server Components: If you want to leverage React Server Components to improve performance by reducing the JavaScript sent to the client, the App Router is the right tool.
• Advanced Navigation: Applications that require parallel routing or more sophisticated navigation will benefit from the App Router’s advanced features.

Conclusion

Both the App Router and Page Router provide unique advantages for building Next.js applications. The Page Router is simple, intuitive, and works well for smaller projects or scenarios where routing requirements are minimal. The App Router, on the other hand, provides more advanced features, including nested layouts, server components, and parallel routing, making it well-suited for larger and more complex projects.

Ultimately, the choice between the two comes down to the specific needs of your application. If you need simplicity and speed, go with the Page Router. If you need flexibility, scalability, and advanced routing capabilities, the App Router is your best bet.

Happy coding!