TypeScript with allowJS and absolute imports fails at runtime

[novascreen]

I've created a repo to reproduce this issue:
https://github.com/novascreen/ncc-ts-allowjs

TypeScript is configured to allowJS, which we need in a project we are transitioning over to TS gradually. We also have baseUrl/paths configured to be able to do absolute imports of modules in src.
The ncc build runs fine and absolute imports of TS files work perfectly, but when running the output we get a Cannot find module for a JS file we tried to import using an absolute import.

In summary:

• relative TS import: ✔
• absolute TS import: ✔
• relative JS import: ✔
• absolute JS import: ❌

I would expect this to either work or hope to get at least an error during build. We can work around this using relative imports for the JS files, but it's easy to accidentally forget and then get a runtime error once the app is built and deployed 😬