使用jQuery，JSON和AJAX，codeigniter填充子菜单下拉菜单

<select id="parentMenu">
  <option value="">请选择</option>
  <option value="1">菜单1</option>
  <option value="2">菜单2</option>
  <option value="3">菜单3</option>
</select>

<select id="childMenu">
  <option value="">请选择</option>
</select>

$(document).ready(function() {
  $('#parentMenu').change(function() {
    var parentId = $(this).val();
    
    $.ajax({
      url: '菜单控制器的URL',
      type: 'POST',
      dataType: 'json',
      data: {parentId: parentId},
      success: function(data) {
        // 清空子菜单下拉框
        $('#childMenu').empty();
        
        // 填充子菜单下拉框
        $.each(data, function(key, value) {
          $('#childMenu').append('<option value="' + value.id + '">' + value.name + '</option>');
        });
      }
    });
  });
});

class MenuController extends CI_Controller {
  public function getChildMenu() {
    $parentId = $this->input->post('parentId');
    
    // 根据父菜单ID查询子菜单数据，这里假设使用数据库查询
    $childMenuData = $this->db->get_where('child_menu', array('parent_id' => $parentId))->result_array();
    
    // 返回JSON格式的子菜单数据
    echo json_encode($childMenuData);
  }
}

$route['menu/getChildMenu'] = 'menuController/getChildMenu';