I don't know if this is correct for the Mac version for avast, but detections in windows for this JS:Blacole some of these detections have been corrected.
Ensure that you have the latest avast virus definitions as this detection has now been corrected.
Deletion isn't really a good first option (you have none left), 'first do no harm' don't delete, send virus to the chest (a protected area) and investigate.