store to localstorage on visibilty change

[rubenmoor]

https://stackoverflow.com/questions/67028712/how-to-get-a-reflex-event-that-fire-on-visibilitychange-of-document

maybe similar to this code:

eReqResult <- postRender $ do
    fileReader <- liftJSM newFileReader
    let encoding = Just ("utf8" :: String)
    performEvent_ $ eFile <&> \f -> readAsText fileReader (Just f) encoding
    eText <- fmap catMaybes $
      wrapDomEvent fileReader (`on` load) $
        liftJSM $ do
          v <- getResult fileReader
          (fromJSVal <=< toJSVal) v
    dynEitherText <- holdDyn (Left "no file") (Right . Text.unpack <$> eText)
    postConfigNew dynEitherText (void eText)