Re: visibilitychange event

Generally ok, given it is a global listener and you probably just install it once on app initialization. However you should use $doc instead of document to make sure you listen on the global document. Depending on your browser support you might want a utility method to check if visibility change events are actually supported by the browser.

static native boolean isSupported() /*-{
  return $doc.hidden !== 'undefined' && $doc.visibilityState !== 'undefined';
}-*/;

In our app we created a PageVisibilityChangedEvent which extends GwtEvent and then fire it on the app wide EventBus so everyone can easily listen for it. To register the DOM handler we used 

Element doc = Document.get().cast();
DOM.sinkBitlessEvent(doc, VISIBILITY_CHANGE_EVENT);
DOM.setEventListener(doc, new EventListener() {
  @Override
  public void onBrowserEvent(final Event event) {
    if (VISIBILITY_CHANGE_EVENT.equals(event.getType())) {
     firePageVisibilityChangedEvent();
   }
 }
});

You could of course also use elemental2 (requires newest GWT) or JsInterop to reduce the amount of JSNI if that is important for you.

-- J.

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