从javascript中检索变量到控制器的函数中

Question

我在名为people_amount的控制器中调用此函数时遇到问题

//function inside people_amount controller
function ajax_amount($cName)
{
    $this->db->select('Amount');
    $this->db->where('Country_Name', $cName);
    $result = $this->db->get('tb_country');
    $amount = $result->row('Amount');
    echo json_encode($amount) ;
}

这是我的js

<script type="text/javascript">
jQuery( document ).ready(function() {
    function changeTest(obj){
         //get name from dropdown
         $cName = (obj.options[obj.selectedIndex].value);

         //call function to get amount
         $amount = $this->ajax_amount($cName);
    }
});
</script>

这是我的观点

<div class="col-md-6">
    <?php
         $atribut_blangko = 'class="form-control" onChange="changeTest(this)"';
         $selectedBlangko = $values->ID_Blangko;
         echo form_dropdown('ID_Blangko', $dropdown_Blangko, $selectedBlangko, $atribut_blangko);
     ?>
</div>

<div class="col-md-6">
//show the amount in the form input
    <?php echo form_input('Amount', $getAmountfromJS, 'id="amount" class="form-control" readonly="true"') ?>
</div>

我在这里尝试的是当我从下拉列表中选择一个名称时，输入表单将显示所选名称的金额。我该怎么做呢？任何帮助将非常感谢。感谢