Add days to calendar while onEventMoving or onEventResizing

I'm trying to get the calendar to extend when moving or resizing an event. Not sure if this can be done, but I got some errors while I tried:

onEventMoving: function(args) {
    if (args.end >= $scope.dp.visibleEnd()) {
        $scope.dp.days = $scope.dp.days + 5;
        $scope.dp.update();
    }
}

The errors are attached in the screenshot below. Not sure if I need to do anything extra or not.