With the introduction of ShadowDOM, tracking active focus elements on the page
for the purposes of accessibility features has been complicated. FocusObserver
is intended to simplify observation of focus changes that span the full depth of
the accessibility tree, including parts of the tree within shadow roots.
FocusObserver has an interface that is modeled after MutationObserver.
var focusObserver = new FocusObserver(function onFocus(event) {
console.log('The current active element is', event.activeElement);
console.log('The active element\'s root is', event.activeRoot);
console.log('The active element\'s host is', event.activeHost):
});
// Connect the focus observer..
focusObserver.observe();
// Disconnect the focus observer..
focusObserver.disconnect();