At https://www.mediawiki.org/wiki/Talk:Beta_Features/Hovercards I typed a draft, decided to discard it, and closed the tab.
There was no warning about "This page is asking you to confirm that you want to leave - data you have entered may not be saved."
My preference for this is enabled, and there should have been a warning. It was previously fixed in T60402: Flow: Flow should recognise and follow wpuseeditwarning
Users are not prompted for confirmation that they will lose data , if they try to leave an active Flow edit-session (e.g., close the tab, press the back button, left-click a link, etc).
It should display a browser-warning, as it will currently do if we edit and then try to leave a standard page (try wikitext and visualeditor)
(Note: It used to work, in wikitext at least.)
I write a many text in topic on the laptop and when I finish accidentally click on the link "GFDL" which is directly above the button. Once the page is refreshed - opens a new page GFDL and all typed data are lost.
There should be a check on the non-empty field.