Ok but `settings` in prefs.js still has global issue. The reason we don't want to that is garbage collection. It won't get garbage collected after window close. To fix that move line 12 (prefs.js) to `fillPreferencesWindow()` and `buildPrefsWidget()`. Also make `settings` local. then you can use dependency injection for `prefsWidget` and `PrefsWindow`. Also you can pass that as an argument to the functions they need it.