gistfile1.js

var states = new Array();
<% for region in @regions -%>
  states.push(new Array(<%= region.parent_id || '-1' %>, '<%=h region.name %>', <%= region.id %>));
<% end -%>

$(document).ready(function() {
  $('#ad_root_region_id').change(function() {  
     country_id = parseInt( $('#ad_root_region_id').val() );
     var options = '<option></option>';

     for (i=0;i < states.length;i++) {
       if (country_id == states[i][0]) {
        options += '<option value="' + states[i][2] + '">' + states[i][1] + '</option>';
       }
     }
     $("#ad_region_id").html(options);
  });
});