Source Maps don't work for `js` or `jsx` files in live dev mode.

[shobhitg]

Hi,

Source maps do not work if I add a .js or .jsx file and then try to do live dev using yarn start.

This works in yarn build however.

I have a sample repo here to reproduce the issue:
https://github.com/shobhitg/source-map-issue/

Its basically a fresh project. Only thing I did is rename App.tsx to App.jsx.

With App.tsx, it works:

With App.jsx, it doesn't work:

Is this a known issue?
If yes, is there some workaround by which I can get source maps to work with .jsx files?