Epubreader save bookmark does not work on iOS

Any browser running on an iOS device won’t update the bookmark/progress feature with the epubreader. I tested on iPad Mini 6, iPad Pro 2nd gen, and MacBook air. It seems to work fine on my Windows computers and Android phone. I think I traced it back to the event window.onbeforeunload in the epubreader.js. Researching it brings up that a number of browsers/systems don’t support/aren’t compatible with that event. I tested adding these:

document.addEventListener('visibilitychange', function() {
if (document.visibilityState === 'hidden') {
$scope.storeBookmark();
}
});

setInterval($scope.storeBookmark, 60000); // Save every 60 seconds

and it is now updating reading progress on epubs in the browser reader.
Hopefully this is helpful. Let me know if you need any help narrowing it down further or testing.