动态获取选择框中的数据编码器

我有两个选择框，如果我选择一个选项，它会根据选项给我结果，然后结果将显示在第二个选择框。我该怎么做呢?我想，我必须做一个onchange函数，但我不知道如何在JavaScript中从控制器获取数据。

class StockInController extends MY_Controller {
    function index(){
        $data['main_content'] = 'stockInView';
        $this->load->model('supplierModel');
        $query = $this->supplierModel->getAllSuppliers();
        if ($query){
            $data['records1'] = $query; 
        } 
        $this->load->model('categoryModel');
        $query = $this->categoryModel->getAllCategories();
        if ($query){
            $data['records2'] = $query;
        }
        $this->load->model('itemsModel');
        $query = $this->itemsModel->getAllItems();
        if ($query){
            $data['records3'] = $query;
        }
        $this->load->view('dashboardTemplate/template',$data); 
    }
    function addStockIn(){
        //getting parameters from view 
        $data = array(
            'item_name' => $this->input->post('item_name'),
            'cat_id' => $this->input->post('cat_id')        
        );
        //$is_ajax = $this->input->post('ajax'); //or use this line
        //$this->input->is_ajax_request();
        $result = array();
        $this->load->model('stockInModel'); 
        $query = $this->stockInModel->addStocktoDB($data);
        if ($query){  //&& any other condition
            $result['res'] = 1;//process successful - replace 1 with any message
        } else {
            $result['res'] = 0;//process failed - replace 0 with any message
        }
        echo json_encode($result);//at the end of the function.
    }
}

视图如下:

<div class="control-group">
    <label for="selsear" class="control-label">Select a Category</label>
    <div class="controls">
         <select name="select1" id="seslsear" class='cho'>
            <option id = "y" value="0">--Select--</option>
            <?php foreach($records2 as $r) { ?>
            <option value="<?=$r->cat_id?>"><?=$r->cat_name?></option>
            <?php } ?>
        </select>
    </div>
</div>
<div class="control-group">
    <label for="selsear" class="control-label">Select an item</label>
    <div class="controls">
        <select name="select1" id="selsear" class='cho'>
            <option id = "y" value="0">--Select--</option>
            <?php foreach($records3 as $r) { ?>
            <option value="<?=$r->item_id?>"><?=$r->item_name?></option>
            <?php } ?>
        </select>
    </div>
</div>