function ShowAuthor(elem, author) {
  if (elem != null && author != null) {
    document.getElementById(elem).innerHTML = "<br />Author: " + author;
    document.getElementById(elem).style.display = 'block';
  }
}

function HideAuthor(elem) {
  if (elem != null) {
    document.getElementById(elem).style.display = 'none';
  }
}