JEASYUI : Mengirimkan parameter javascript via combobox jeasyui

Combobox
<div id="resultzen" class="fitem">
                <label>Customer Type</label>
                    
                     <select name="m_CustType_ID" id="m_CustType_ID" class="easyui-combobox" required="true" >
                                                 <?
foreach ($custipe as $resulejs) {
?>
            <option value="<?= $resulejs['CustType_ID']; ?>"><?= $resulejs['Nama_CustType']; ?>
            </option>
            <?php
}
?>
        </select>
     
            </div>


Function Javascript mengirim data POST
function refreshdif(){
$.ajax({type:"POST",url:"<?=site_url() ?>/masterp/getcombo",data:{m_CustType_ID:$('#m_CustType_ID').combobox('getValue')},success:function(a){$("#resultzen").html(a)}})}