search.js

$(function(){
  $("select#search_country_id").change(function(){
    $("img#spinner_city_id").show();
    $("select#search_city_id").disable();
    $.getJSON("/cities.json",{country_id: $(this).val(), ajax: 'true'}, function(j){
      var options = '';
      for (var i = 0; i < j.length; i++) {
        options += '<option value="' + j[i]["city"]["id"] + '">' + j[i]["city"]["name"] + '</option>';
      }
      $("select#search_city_id").html(options);
      $("select#search_city_id").enable();
      $("img#spinner_city_id").hide();
    })
  })
})