Error when running npm run lint react-router

[aaronbeall]

I don't know if this is an issue with my local environment but when I try to run npm run lint react-router (or for other React related libraries) I get this error:

Error: Errors in typescript@3.9 for external dependencies:
../react/index.d.ts(36,22): error TS2307: Cannot find module 'csstype' or its corresponding type declarations.

I tried this with a fresh clone of DT as well as with my own fork. I noticed that the CI build doesn't seem to have this issue.

[aaronbeall]

I figured it out. react is imported by react-router (not surprisingly) which is defined in DT, so comes from types/react, and types/react has it's own package.json that lists csstype as an external dependency (not in DT). I needed to npm install from types/react to get the full dependencies for react-router. This makes sense now, but it was a bit of a surprise.

[davidje13]

For future people finding this issue (like me!), the same error message is currently appearing when using @types/react in a project due to a mistake in 16.14.1, fixed in #49717 (not yet published). In the meantime, downgrading to @types/react@16.14.0 fixes it.