importing ts files with js extension does not work

[dominikg]

a.ts

import './b.js' 

b.ts

console.log('hello from imported')

tsx a.ts results in an error that b.js cannot be found.

Expected behavior:
Resolve and transpile b.ts when importing as b.js

Additional info:
similar issue that was resolved in vite repo: vitejs/vite#6671
info in typescript repo why this is expected to work: microsoft/TypeScript#46452

This used to work in esmo, discovered it didn't when switching to tsx in vite-ecosystem-ci, workaround was to use b.ts instead for importing.