javascript - How to call controller from ajax and send $_POST -

i want call controller ajax , send post database. after post sent, display database dropdown list.

but don't know do. here code.

ajax script inside view add_produk.php

<script>     function getid(val){         // ajax function         $.ajax({             type: "post",             url: "<?php base_url();?>index.php/getdata",             data: "id_kategori="+val,             success: function(data){                 $("#subcat").html(data);             }         });     } </script> 

i want load controller getdata.php , send $_post controller, controller getdata.php :

<?php if ( ! defined('basepath')) exit('no direct script access allowed');   class getdata extends ci_controller {      public function index()     {         if(!empty($_post["id_kategori"])){             $idcat = $_post["id_kategori"];             $sql = "select * sub_kategori id_kategori = $idcat";             $result = $this->db->query($sql);              foreach ($result $subcat) {                  ?>                 <option value="<?php echo $subcat["id_sub_kategori"];?>"><?php echo $city["nama_sub_kategori"];?></option>                  <?php             }         }     } } ?> 

how can fix problem?

i think wrong in here data: "id_kategori="+val dont know php, u can try "data:{id_kategori:val}" luck