Exactly what versions of npm and ionic to make this sample to work on Mac?

Exactly what versions of npm and ionic to make this sample to work on Mac? I have struggled weeks trying to make this PWA work: https://github.com/driftyco/ionic-conference-app

I followed the instructions but either I got “Ionic not found” even if it was installed successfully. If I switched to the newest, “ionic serve” will throw errors like “There was an error serving your Ionic application: There was an error with the spawned command: serve”.

I did not expect ionic is so difficult to start. For weeks I had no luck to get ionic serve to work. So Exactly what versions of npm and ionic to make this sample to work on Mac?

Thanks in advance.