Nextjs Custom Error Pages Complete Guide

Explain in Details and Show Important Info: Next.js Custom Error Pages

1. Understanding Default Error Pages

• Development Environment: In the Next.js development mode, if there’s an error on both client and server-side, it'll display a detailed overlay with information about the issue.
• Production Environment: Post-build and deployment, Next.js automatically serves:
  • 404 Page: When a user navigates to a non-existent route.
  • 500 Page: For server-side errors (internal server errors).

These default setups help during the development phase and initial deployment but might not be suitable for production, where you'd want to have a cleaner and more user-friendly UI.

2. Creating a Custom 404 Page

• To create a custom 404 page, simply add a file named 404.js inside the pages/ directory.
• Example Code:

  // pages/404.js
  export default function Custom404() {
    return (
      <div>
        <h1>Sorry, we couldn’t find that page!</h1>
        <a href="/">Return to homepage</a>
      </div>
    )
  }
  

• Styling: You can style this page using CSS Modules, global styles, or any other styling framework like Tailwind CSS.
• Best Practices: Include clear navigation options (like a link back to the home page) to help users explore your site and reduce bounce rates caused by encountering a 404 error.

3. Creating a Custom 500 Page

• Similarly, a custom 500 page is created by adding a 500.js file in the pages/ folder.
• Example Code:

  // pages/500.js
  import Link from 'next/link';
  
  export default function ServerError() {
    return (
      <div>
        <h1>Unexpected Error! Please try again later.</h1>
        <Link href="/">
          <a>Return Home</a>
        </Link>
      </div>
    )
  }
  

• Handling Errors: Since the 500 page typically indicates an internal server error, use it as an opportunity to log the user action or device information for further analysis.
• User Communication: Inform users about the system status and suggest alternative actions they could take.

4. Dynamic and Static Custom Error Pages

• Static Custom Error Pages: These are regular Next.js pages that render static content. They are useful for simple custom 404 and 500 pages without dynamic interactions. Example: pages/404.js as shown above.

• Dynamic Custom Error Pages: While the default behavior provides minimal dynamic handling, you can still incorporate some dynamic elements or data fetching.

  // pages/404.js
  export default function Custom404({ errorCode }) {
    return (
      <div>
        <h1>{errorCode ? `Error ${errorCode}` : '404 Error'}</h1>
        <p>We couldn't find what you are looking for, sorry!</p>
      </div>
    )
  }
  
  Custom404.getInitialProps = ({ res, err }) => {
    const statusCode = res ? res.statusCode : err ? err.statusCode : null;
    return { errorCode: statusCode };
  }
  

5. Using API Routes for Handling Errors

• Advanced error handling might involve using API routes to send error logs to monitoring services directly from the 404 or 500 pages.

// pages/500.js
import Link from 'next/link';
import fetch from 'isomorphic-unfetch';

export default function ServerError() {
  const sendErrorLogs = async () => {
    try {
      await fetch('/api/error-log', {
        method: 'POST',
        body: JSON.stringify({
          errorType: '500', 
          additionalData: 'More details about the error'
        })
      });
    } catch (error) {
      console.error('Failed to send error logs:', error);
    }
  };

  useEffect(() => {
    sendErrorLogs();
  }, []);

  return (
    <div>
      <h1>Oops! Something went wrong...</h1>
      <Link href="/"><a>Return to Homepage</a></Link>
    </div>
  );
}

• API Route Implementation:

export default async function handler(req, res) {
  if (req.method !== 'POST') {
    res.status(405).json({ message: 'Method not supported' });
    return;
  }

  // Extracting error data from request body
  const { errorType, additionalData } = req.body;

  try {
    await sendToMonitoringService(errorType, additionalData); // Your custom function to send logs
    res.status(200).json({ status: 'success' });
  } catch (error) {
    res.status(500).json({ message: 'Server error occurred while logging' });
  }
}

6. Best Practices for Custom Error Pages

• Consistent Branding: Ensure that your custom error pages align with your site’s branding guidelines, including colors, fonts, and imagery.
• Clear Messaging: Provide users with clear messages indicating the nature of the error and what they can do next.
• Responsive Design: Make sure your custom error pages are mobile-friendly and work across all browsers.
• SEO Considerations: Although unlikely to be indexed by search engines due to their temporary nature, ensure your error pages don’t include unnecessary keywords or tags that could confuse crawlers.

7. Testing Custom Error Pages

• Thoroughly test your custom error pages to ensure they handle various scenarios gracefully.
• For the 404.js file, test by visiting non-existent URLs.
• For the 500.js file, simulate server-side errors (e.g., by throwing exceptions in getServerSideProps or API routes).

8. Important Notes and Limitations

• Static Generation: Custom error pages (404.js and 500.js) must be statically generated. This means you can’t use hooks like useRouter or useState at the top level of these files.
• Global Customization: If you wish to apply specific styles or layouts to all pages, including your custom error pages, consider defining a _app.js file in the pages/ directory to wrap your pages with a consistent layout or design.

  // pages/_app.js
  import '../styles/globals.css'
  
  function MyApp({ Component, pageProps }) {
    return <Component {...pageProps} />
  }
  
  export default MyApp
  

By following these steps and incorporating these best practices, you can create custom error pages in Next.js that not only improve the user experience but also facilitate better error management and analytics.

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