gistfile1.txt

addLoadEvent(function() {
  var dropdowns = form.getElementsByTagName("select");
    for(var i = 0; i < dropdowns.length; ++i) {
      dropdowns[i].onchange = function() {
        if(dropdowns[i].value != "") {
          if(document.getElementsByClassName(dropdowns[i].id).length == 0) {
            var input = document.createElement("input");
            input.type = "hidden";
            input.className = dropdowns[i].id;
            input.name = "lists[]";
            input.value = "108";
            form.appendChild(input);
          }
        } else {
          var input = document.getElementsByClassName(dropdowns[i].id);
          if(input.length != 0) {
            input[0].parentNode.removeChild(input[0]);
          }
        }
      }
    }
  });