HeaderDragStart Property

// The client event 'HeaderDragStart' takes two parameters sender and e
// sender  is the object which is raising the event
// e is the HeaderDragStartEventArgs 
  function WebDataGrid_HeaderDragStart(sender, e) {

      //Gets the column object you want to move
      var column = e.get_column();

      //Gets the key of the column
      var key = column.get_key();

      //Gets the index of the column
      var index = column.get_index();

      if (!confirm("Are you sure you want to move the column '" + key + "' from the index '" + index + "' ?"))

          //Cancels the HeaderDragStart event
          e.set_cancel(true);
               
  }