Detecting when the window is closing when quitOnLastWindowClosed is off

[DizzyHSlightlyVoided]

So, I'm trying to write an app with quitOnLastWindowClosed disabled in Node.js, so that I can open an error-window after the main window is closed/hidden if necessary. I can call quitEventLoop() manually when necessary in, say, the cancel-button and other places; the problem is, it never quits the event-loop if I close the window using alt+F4 or in the minimize/maximize/close box or any other way that isn't directly handled in the code. Is there something I'm missing/somewhere else I should be looking here?