Event name is case insensitive.

This event calls user-defined handlers (if there are any) and passes the following parameters:

• by - a template of sort-by field
• dir - a direction of sorting
• as - a type of sorting

  chart.attachEvent("onBeforeSort", function (by, dir, as){
       //any custom logic here
  });

Event can be blocked, returning false will prevent normal reaction of component.