HMR crashes with "Cannot access 'routes' before initialization" when editing large `.mdx` files using `virtual:react-router/server-build`

[nikolailehbrink]

I'm using React Router as a...

framework

Reproduction

https://stackblitz.com/edit/github-pvha4jzr?file=app%2Froutes%2Fblog%2Fshort-article-without-error.mdx

1. Start the dev server.
2. Navigate to /blog/long-article or click on the Long Article with HMR error link on the homepage
3. Add content to long-article-with-error.mdx route file (e.g., repeated paragraphs).
4. Save the file.
5. Observe crash:

   ReferenceError: Cannot access 'routes' before initialization
   

Important

The crash sometimes does not occur after every save

This only happens when the MDX file exceeds a certain content length. Smaller files do not trigger this issue. To test this, you can do the same thing with /blog/short-article

Note

The getPosts function used in the loader of layout.tsx is not causing the error as I initially suspected, even though it imports virtual:react-router/server-build. This part can be removed from the repro, but I included it to show how it's set up in a real-world scenario.

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (16) x64 AMD Ryzen 7 5800X 8-Core Processor
    Memory: 50.57 GB / 63.93 GB
  Binaries:
    Node: 22.14.0 - C:\nvm4w\nodejs\node.EXE
    npm: 10.9.2 - C:\nvm4w\nodejs\npm.CMD
    pnpm: 9.5.0 - ~\AppData\Local\pnpm\pnpm.EXE
  Browsers:
    Edge: Chromium (133.0.3065.59)
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    @react-router/dev: ^7.5.3 => 7.5.3
    @react-router/node: ^7.5.3 => 7.5.3
    @react-router/serve: ^7.5.3 => 7.5.3
    react-router: ^7.5.3 => 7.5.3
    vite: ^6.3.3 => 6.3.4

Used Package Manager

pnpm

Expected Behavior

Hot Module Reloading should:

• Reload the changed .mdx file.
• Update the browser without full reload or crashing.
• Not throw any errors from virtual:react-router/server-build.

Actual Behavior

When the .mdx file exceeds a certain size:

• The app crashes after saving the file, disabling HMR.

• Console error shows:

  ReferenceError: Cannot access 'routes' before initialization
  

• Stack trace indicates virtual:react-router/server-build is being accessed too early during HMR cycle.

[nicksrandall]

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