But be careful because it seems very easy to lose data. At least in my testing, if you create a new page but don't save and close the tab then you lose all data without any warnings. Similarly, if you are in the middle of adding content to a page and close the tab then it is gone without any confirmation box. A built-in browser confirmation box when closing tab/window should be relatively easy to add in I think.
Tiddlywiki will prevent a page close, this does not and will lose the entire wiki. Feather warns on not saving individual pages, but saving in this context means so little, this should just be part of the ephemeral internal state. No saving required. Save to disk is the only permanent storage and Feather doesn't have any guardrails here.
I don't do browsers, but can locally loaded file set cookies and/or use browser storage? I shouldn't ever have to consciously think about saving a file, let alone an entire wiki in 2022.