var tableCellVal = function(node) {
  return $(".val", $(node)).text();
};

var addTableSort = function() {
  $("table.sortable").tablesorter(
    {
      sortList: [[0,0]],
      headers: { 1: {sorter: false} }, 
      textExtraction: tableCellVal
    }
  );
};

$(document).ready(function() {
  addTableSort();
});