Is there a basePath bug in Next.js 16?

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Summary

The issue at hand is related to basePath configuration in Next.js 16. When a basePath is specified in next.config.mjs, serving assets from the /public directory using the Image component does not work as expected. Instead of automatically handling the basePath, the asset path needs to be manually prefixed with the basePath value.

Root Cause

The root cause of this issue can be attributed to the following:

  • The basePath configuration in Next.js 16 does not automatically handle asset paths for the Image component.
  • The assetPrefix option is set to basePath in production, but this does not seem to affect the Image component’s behavior.
  • The need to manually prefix the asset path with basePath suggests a potential basePath bug in Next.js 16.

Why This Happens in Real Systems

This issue can occur in real-world systems when:

  • Deploying a Next.js application to a custom server with a non-root basePath.
  • Serving assets from the /public directory using the Image component.
  • The basePath configuration is not properly handled by the Image component.

Real-World Impact

The impact of this issue can be significant, leading to:

  • Broken asset links: Assets may not be served correctly, resulting in broken links and a poor user experience.
  • Increased development time: Developers may need to spend extra time troubleshooting and manually prefixing asset paths.
  • Decreased performance: Manually prefixing asset paths can lead to decreased performance and increased maintenance costs.

Example or Code

// next.config.mjs
const isProd = process.env.NODE_ENV === "production";
const defaultProdBasePath = "/MyNextEMailApp";
const basePath = isProd? process.env.NEXT_BASE_PATH?? defaultProdBasePath : "";
const nextConfig = {
  output: "standalone",
  basePath,
  assetPrefix: isProd? basePath : undefined,
  trailingSlash: true,
  env: {
    NEXT_PUBLIC_BASE_PATH: basePath,
  },
};
export default nextConfig;

How Senior Engineers Fix It

Senior engineers can fix this issue by:

  • Manually prefixing asset paths: Using the basePath value to prefix asset paths, as shown in the example code.
  • Configuring assetPrefix correctly: Ensuring that the assetPrefix option is set correctly in next.config.mjs.
  • Testing and verifying: Thoroughly testing and verifying that assets are served correctly with the basePath configuration.

Why Juniors Miss It

Junior engineers may miss this issue due to:

  • Lack of experience: Limited experience with Next.js and basePath configuration.
  • Insufficient testing: Inadequate testing and verification of asset serving with basePath.
  • Misunderstanding of documentation: Misinterpretation of the Next.js documentation regarding basePath and asset serving.