[mikece]

If the purpose is to just run JavaScript code on Android outside of a browser context, React Native and NativeScript have been doing this for a while.

If the purpose is to run JavaScript functions as background services this is somewhat implemented via Service Workers in Progressive Web Apps.

I don't think there is any way (currently) to register a JavaScript function/library as an always-on server process. I don't see why this would be unsafe or particularly undesirable unless there is something computationally intensive happening.