Office.VisibilityMode enum  
Visibility mode of the add-in.
Remarks
Examples
Office.onReady(() => {
    Office.addin.onVisibilityModeChanged((args) => {
        if (args.visibilityMode === Office.VisibilityMode.taskpane) {
            // Do something when the task pane is visible.
        }
    });
    // Other startup tasks.
});
Fields
| hidden = 'Hidden' | UI is hidden. | 
| taskpane = 'Taskpane' | Displayed as a task pane. |