SPA Mode not working with `serverModuleFormat: cjs`

[krsilas]

I'm using React Router as a...

framework

Reproduction

• Go to https://stackblitz.com/edit/stackblitz-starters-6zkc9f?file=react-router.config.ts
• If dev server starts automatically, stop the dev server
• Run pnpm run build -> build/client/index.html is generated as part of build because of ssr: false
• Enable serverModuleFormat: "cjs" in react-router.config.ts
  (because even though the server build is deleted after running the build in ssr: false, ssr is used for initial prerendering and some third party libraries don't have good esm support)
• Run pnpm run build again -> Error:

  [react-router] exports is not defined in ES module scope
  This file is being treated as an ES module because it has a '.js' file extension and '/home/projects/stackblitz-starters-6zkc9f/package.json' contains "type": "module". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.

• Rename react router config to react-router.config.cjs
• Run pnpm run build again

System Info

See stackblitz environment

Used Package Manager

pnpm

Expected Behavior

When config contains ssr: false and serverModuleFormat: "cjs", the build does not fail and renders static html.

Actual Behavior

Error instructs to rename config to react-router.config.cjs but .cjs file is ignored and default config is being used -> ssr: true.

[brophdawg11]

What is the reason for using a CJS server build while using type:'module'? If you remove type:'module' I think this works as expected: https://stackblitz.com/edit/stackblitz-starters-mymkczh5?file=react-router.config.ts

[github-actions]

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