I'm using OSX 10.11.2.
When I am using Boostnote in full screen, if I push the window close button or enter command + w, Boostnote will not closed. And, screen is become black. I thought that this cause was Electron, because Slack does the same thing too. However Atom, VSCode, HyperTerm did not such a thing. So, this cause should be not Electron.

I am using Ubuntu 16.04.2 and Windows 10. So far I couldn't reproduce your bug. This may be platform-specific. @sosukesuzuki
Thank you for your reporting @VoLuong san!
I also have occurred the bug same as Sosuke. *macOS Sierra v10.12.3
This bug may be occurred in mac only, but we'll look it up.
This is not a bug, it's the expected behavior of an app on macOS. Generally on Windows and Ubuntu apps get closed when you click on that close button but on macOs apps keep running in background.
@akashnimare Nah, you got the issue wrong. It's not that the app didn't close that they were complaining about. Look at the GIF and see how the screen turns black after pressing the close button.
Actually, the behavior is correct for electron. And you, check them https://github.com/electron/electron/pull/7817, https://github.com/BoostIO/Boostnote/pull/349.
It will be fixed on next release.
Most helpful comment
Actually, the behavior is correct for electron. And you, check them https://github.com/electron/electron/pull/7817, https://github.com/BoostIO/Boostnote/pull/349.