Oh snap, good catch, thanks! Fixed!
The method was supposed to be private all along, I just missed the underscore in the first code block. The underscore has always been an indicator of “privacy” in methods in various languages, so I used it here as convention. The checkState method isn’t meant to be used by anything outside this “library”, so marking it as private like so was only logical. It’s also a sort of precursor to a further upgrade to the whole matter of this extension - building React components to simplify Trello UI customization even further.