Don't store any property if you don't want to clean that up in window close request (line 17 `prefs.js`): EGO Review Guidelines: Destroy](https://gjs.guide/extensions/review-guidelines/review-guidelines.html#destroy-all-objects)

Thank you for the review. The link you gave me only describes this process for the main extension class. Could you tell me, how I can clean it up for the preferences class? I also thought that a variable initialized with `this.getSettings()` would not need to be destroyed as the documentation only nullifies it in the extension class: [GNOME Extension Preferences: Integrating Settings](https://gjs.guide/extensions/development/preferences.html#extension-js)

You can make it local to `fillPreferencesWindow()` and pass it to the methods needing that. or you can: ```js window.connect('close-request', () => { // clean up here }); ```