code: function appendTd(tr, text, classNames) {
    let td = document.createElement('td');
    let cell = document.createTextNode(text);
    td.appendChild(cell);
    tr.appendChild(td);
    if(classNames) {
      td.setAttribute('class', classNames);
    }
  }
docs: Append a <td> with the given content to the given <tr>