code: function exitFullScreen() {
      if (Windows.UI.ViewManagement.ApplicationViewBoundsMode) { // else crash on 8.1
          var view = Windows.UI.ViewManagement.ApplicationView.getForCurrentView();
          view.setDesiredBoundsMode(Windows.UI.ViewManagement.ApplicationViewBoundsMode.useVisible);
          view.suppressSystemOverlays = false;
      }
  }
docs: Exit fullscreen mode