These docs are for an old release.
Info on upgrading to v4
loading
Triggered when event or resource fetching starts/stops.
function( isLoading, view )
Triggered with a true argument when the calendar begins fetching events via AJAX. Triggered with false when done.
view is the current View Object.
This function is often used to show/hide a loading indicator.
When the Scheduler plugin is loaded, this callback is also fired when resources are fetched.