sets the Jet App class for the widget
|app||object||Jet App class|
The method is not intended to be called directly. It just points to the class of the Jet App which is used as a base for this widget.
After initialization, the instance of the inner Jet App class can be accessed via the $app property:
const app = $$("myfilemanager").$app;
You can read more about Jet App within Filemanager in the corresponding section.