var adPositions = {};
function writeAdDiv(name) {
  document.write('<div id="'+name+'-beacon"></div>');
  adPositions[name] = name;
}
function positionAds() {
  for (ad in adPositions) {
    var oldDiv = document.getElementById(ad);
    var newDiv = document.getElementById(ad+'-beacon');
    newDiv.parentNode.replaceChild(oldDiv, newDiv);
  }
}