When editing Wikidata, in case of accidentally closing the browser window, no confirmation is asked and all changes that were not saved are lost.
Steps to reproduce:
- Start editing an item, for example in the sandbox
- Force closing the window (Ctrl+W, Alt+F4)
- No confirmation dialog is shown, the window is closed immediately
On the contrary, when editing Wikipedia with the visual editor, or any page using the regular Mediawiki wikicode editor, the usual browser window ("This page is asking you to confirm that you want to leave - data you have entered may not be saved. Stay on the page / Leave page") appears.