HTML Sort Table by clicking header

I am trying to write a script to sort a table by clicking an icon in the header, I've tried copying the code from a different website and when I copy and paste it the table sorts fine but when I apply it to my table it doesn't work. I've copied and pasted the relevant code into this link: https://codepen.io/bawsmith/pen/gOzxbyz

    function sortTable(n) {
  var table,
    rows,
    switching,
    i,
    x,
    y,
    shouldSwitch,
    dir,
    switchcount = 0;
  table = document.getElementById("myTable");
  switching = true;
  //Set the sorting direction to ascending:
  dir = "asc";
  /*Make a loop that will continue until
  no switching has been done:*/
  while (switching) {
    //start by saying: no switching is done:
    switching = false;
    rows = table.getElementsByTagName("TR");
    /*Loop through all table rows (except the
    first, which contains table headers):*/
    for (i = 0; i < rows.length - 1; i++) { //Change i=0 if you have the header th a separate table.
      //start by saying there should be no switching:
      shouldSwitch = false;
      /*Get the two elements you want to compare,
      one from current row and one from the next:*/
      x = rows[i].getElementsByTagName("TD")[n];
      y = rows[i + 1].getElementsByTagName("TD")[n];
      /*check if the two rows should switch place,
      based on the direction, asc or desc:*/
      if (dir == "asc") {
        if (x.innerHTML.toLowerCase() > y.innerHTML.toLowerCase()) {
          //if so, mark as a switch and break the loop:
          shouldSwitch = true;
          break;
        }
      } else if (dir == "desc") {
        if (x.innerHTML.toLowerCase() < y.innerHTML.toLowerCase()) {
          //if so, mark as a switch and break the loop:
          shouldSwitch = true;
          break;
        }
      }
    }
    if (shouldSwitch) {
      /*If a switch has been marked, make the switch
      and mark that a switch has been done:*/
      rows[i].parentNode.insertBefore(rows[i + 1], rows[i]);
      switching = true;
      //Each time a switch is done, increase this count by 1:
      switchcount++;
    } else {
      /*If no switching has been done AND the direction is "asc",
      set the direction to "desc" and run the while loop again.*/
      if (switchcount == 0 && dir == "asc") {
        dir = "desc";
        switching = true;
      }
    }
  }
}

Any advise would be appreciated.