ColumnSelectionChanging Property

// The client event ColumnSelectionChanging takes two parameters sender and e
// sender  is the object which is raising the event
// e is the ColumnSelectionChangingEventArgs

   function WDG1_ColumnSelectionChanging(sender, e) {

       //Returns a Read Only collection of the currently selected columns
       var currentSelectedColumns = e.getCurrentSelectedColumns();

       //Returns the number of columns in the collection
       var currentLength = currentSelectedColumns.get_length();

       //Returns a Read Only collection of the newly selected columns
       var newSelectedColumns = e.getNewSelectedColumns();

       var newLength = newSelectedColumns.get_length();

       window.status = "The number of columns selected changed from '" + currentLength + "' to '" + newLength + "'";
   
   
   }