Is there a way to determine when ng build/serve is finished?

In my current project I am working on a Service which internally spawns a process which executes a ng serve or a ng build depending on what the client wants to do with its webapplication.

The problem I am facing right now is that the service does not know when the ng serve or ng build process is finished. Is there a way to deterministically determine when the ng serve/build process is finished?

I found a --buildEventLog flag in Angular version 10 which does exactly what I want but apparently this experimental feature has been removed in the latest version so I am looking for alternatives.

Would love to get some ideas/recommendations how to tackle this problem!