var NUMBER_CARTOONS=4;

function loader() {
 
  var id = getRandomNumber(NUMBER_CARTOONS) + 1;
 
  if (document.getElementById) {
    var elem = document.getElementById("comic");
    if (isEmpty(elem)) return false;
    elem.setAttribute("src", "images/belvedere/" + id + ".gif");
    var elem = document.getElementById("link");
    if (isEmpty(elem)) return false;
    elem.setAttribute("href", "comics.php?id=" + id);
  }
}

function getRandomNumber(maxNumber) {
  return Math.floor(maxNumber*Math.random());
}

function isEmpty(s){  
  return ((s == null) || (s.length == 0))
}