function formatNumber(num) {      if (!/^(\+|-)?(\d+)(\.\d+)?$/.test(num)) {          return num;      }      var a = RegExp.$1, b = RegExp.$2, c = RegExp.$3;      var re = new RegExp().compile("(\\d)(\\d{3})(,|$)");      while (re.test(b))   b = b.replace(re, "$1,$2$3");      return a + "" + b + "" + c;  }