Javascript Ajax请求从未成功，但没有错误

我正在尝试从ajax调用加载下拉列表。这是我的密码：

<select name="customer" onChange="testAJAX(this.value)">
    <option value="0" selected >Select Customer</option>
    <?php
        $services = db_query('SELECT cust_id,cust_name FROM '.CUST_TABLE.' ORDER BY cust_name');

        while (list($cust_id,$name) = db_fetch_row($services)){
            $selected =($info['customer']==$cust_id)?'SELECTED':'';?>
                <option value="<?=$cust_id?>"<?=$selected?>><?=$name?></option>
                    <?php
                     }?>
</select>

}

以及它调用的页面

<?php 

$custID = 0;
$mysqli = new mysqli("localhost", "James", "mypassword", "OSTickets"); 

if (isset($_REQUEST['custID'])) {
    $custID = $_REQUEST['custID'];
}

$sql = 'SELECT l.location_id, l.site_name FROM ost_customer_location' 
. ' AS l JOIN ost_customer'
. ' AS c ON c.cust_id=l.cust_id'
. ' WHERE c.cust_id='.$custID;

$locations = array();

$str = "";
$str .= "<option value='0'>Select Location</option>";
if ($result = $mysqli->query($sql)) {
    while ($row = mysqli_fetch_array($result)){ 
        $str .= "<option value=".$row["0"].">".$row["1"]."</option>";
    }
}
echo $str;
?>

这是来自控制台的响应

---

对象{readyState:4，responseText:“Duke Rd-Primary”，状态：200，状态文本：“OK”}

同时拥有complete（）和success（）/error（）是多余的谢谢，我删除了complete函数，但我仍然得到了problemPHP错误处理？控制台错误？PHP自己工作吗？@godmode不是。有处理成功的代码、处理错误的代码和不管如何运行的代码（例如，删除指示正在进行ajax调用的图标）都很好，您能用一个简单的控制台来确认它没有成功或错误吗？如果打开GoogleDevTools并转到network选项卡，您应该能够看到请求，以及它是否返回了200/404/500

<?php 

$custID = 0;
$mysqli = new mysqli("localhost", "James", "mypassword", "OSTickets"); 

if (isset($_REQUEST['custID'])) {
    $custID = $_REQUEST['custID'];
}

$sql = 'SELECT l.location_id, l.site_name FROM ost_customer_location' 
. ' AS l JOIN ost_customer'
. ' AS c ON c.cust_id=l.cust_id'
. ' WHERE c.cust_id='.$custID;

$locations = array();

$str = "";
$str .= "<option value='0'>Select Location</option>";
if ($result = $mysqli->query($sql)) {
    while ($row = mysqli_fetch_array($result)){ 
        $str .= "<option value=".$row["0"].">".$row["1"]."</option>";
    }
}
echo $str;
?>

<option value='0'>Select Location</option>
<option value='252'>Location 1</option>
<option value='345'>Location 2</option>

error: function(jqXHR, textStatus, errorThrown){ console.log(jqXHR); }