Required library edition:

This event occurs before starting data sorting. onBeforeSorting event passes the following parameters:

• column index
• sorting type (“str”,”int”,”date”)
• direction of sorting (“asc”,”des”)

Event is blockable (if custom code, attached to event, returns value different from true - sorting operation will be blocked)

        grid.attachEvent("onBeforeSorting", function(ind,type,direction){
              //any custom logic here
              return false;
        });