how can stop navigation on the first row and on the last row of row selection from up and down keys?

  if (e.keyCode == 40){ //arrow down
              
             table.$('tr.selected').removeClass('selected');
            tr.next().addClass('selected');
            tr = table.$('tr.selected');
              
            }
            if (e.keyCode == 38){ //arrow up
              
             table.$('tr.selected').removeClass('selected');
               tr.prev().addClass('selected');
               tr = table.$('tr.selected');
            
            }
            data = table.row('tr.selected').data();