function doAction(results) {
  switch(ex_type) {
    case "get_content":
      var myDiv = document.getElementById("content_div");
      myDiv.innerHTML = results;
      break;
    case "dyn_select":
      myOriginal = document.getElementById("city_select_original");
      if (myOriginal.style["display"] == 'inline') {
        myOriginal.style["display"] = 'none';
      }
      myNew = document.getElementById("city_select_new");
      myNew.innerHTML=results;
      myNew.style["display"] = 'inline';
      break;
    case "cat_tree":
      myDiv = document.getElementById(current_node);
      if (myDiv.innerHTML!="") {
        myDiv.innerHTML="";
        myDiv.style["display"] = 'none';
      } else {
        myDiv.innerHTML=results;
        myDiv.style["display"] = 'inline';
      }
      break;
    case "image_viewer":
      var myDiv = document.getElementById("imageViewer");
      myDiv.innerHTML = results;
      myDiv.style["display"] = 'inline';
      break;
  }
}