Ajax调用控制器函数返回空响应

Question

我有一个下拉列表，每当值发生变化时，我都会调用jacascript函数来更改某些值。我正在使用codeigniter，并在javascript中我使用了ajax，并对控制器函数进行了ajax调用。响应是“成功”，但它是空的，即使我在控制器中写回“hi”，响应也是空的。

ajax_operations.php

function getInventory()
    {   echo "hi";
        $table                          ="inventory"
        $inventoryRecordOptionsData     = "";
        $inventoryRecords               = array();
        $option                         ="item_name";

        if($this->input->post('storeId') != "" ){

            //$inventoryRecords = $this->base_model->fetch_records_from($table, array(store_id => $this->input->post('storeId')));
            $query = $this->db->query("SELECT id, item_name FROM dt_inventory WHERE store_id = 34");
            $inventoryRecords = $query->result_array();

            //$inventoryRecords = $this->db->get_where($table,array('store_id' => '35')->result();
            if(count($inventoryRecords) > 0) {

                $inventoryRecordOptionsData = '<option value="">Select '.$option.'</option>';

                foreach($inventoryRecords as $ic) {

                    $inventoryRecordOptionsData = $inventoryRecordOptionsData . '<option value="'.$ic->id.'">'.$ic->item_name.'</option>';

                }

            }
            else{
                $inventoryRecordOptionsData='<option value="">Select '.$option.'</option>';
            }

        }
        echo $option;
        //echo $inventoryRecordOptionsData;

    }

javascript功能

function getInventoryRecords(store_id)
   { //alert(store_id);
       var childId = "items";
       var optionTxt = "items";

       if(store_id > 0) {

       $.ajax({

        type: "post",
        url: "<?php echo site_url();?>/ajax_operations/getInventory",
        data: "storeId="+store_id+"",

        success: function(data, textStatus, xhr) {


            if(data) {

                $('#'+childId).empty();
                $('#'+childId).append(data);

            } else {
                console.log("hi"+data+"hello");
                $('#'+childId).empty();
                alert("empty response");
                $('#'+childId).append('<option value="">No '+optionTxt+' available.</option>');
            }
            $('#'+childId).trigger("liszt:updated");
        }

       });

       } else {

       $('#'+childId).empty();
       $('#'+childId).append('<option value="">Select '+optionTxt1+' First.</option>');
       $('#'+childId).trigger("liszt:updated");
       }
 }

我获得“成功”作为状态。但数据是空的。