Regarding Draft autosave feature.

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Saves draft every 30 seconds on on page unload, so you don't lose whatever you've typed.

For doing this on page leave there is a trick, "ajax" request must be sent synchronously - as browsers don't allow to fully hijack the page unload event - and the event to run it on is "onbeforeunload".

On the javascript side there are two classes DraftQuestion and DraftAnswer that subclass DraftPost.