Only complaints so far: the horizontal scrollbar is a bit thin and hard to grab; and, er, when I click the yellow button at top right (of the three Mac-style blobs) the window disappears entirely without leaving any way I can find (under Gnome) to get it back again.
Terrific work though.
Concertmaster is built over Electron and, as such, it is 100% JavaScript. In fact, it's not a more convenient website only because of Spotify's limitations.
It would be possible to make Concertmaster open source, but it's far from professional - it's more like a hobby I'm keeping for 3, 4 years.
(Concertmaster is more than the client. It has several server-side functions as well.)
After a few seconds, it still freezes for me, so that's one thing I could try to fix :)
https://i.imgur.com/WJZKiUA.png
After that, the GUI elements just don't respond at all. There is no CPU usage, so it's probably not an infinite loop.
I enabled logging, but don't see anything significant.