AJAX调用不返回数据

Question

有人能告诉我为什么名为tellme的div只显示半秒钟的东西......或更少然后什么都不做？我已经尝试了所有方法，但却无法使代码生效。这很有趣，因为我在我的其他页面上有完全相同的代码并且它没有任何问题，所以有任何问题，我试图调用一个AJAX调用，它只是没有工作，它不会使div称为tellme任何东西，它＆＃ 39;只是把它留空......

<script type="text/javascript">
function fireWorkerFixed(userid)
{
    // Create our XMLHttpRequest object
    var hr = new XMLHttpRequest();
    // Create some variables we need to send to our PHP file
    var url = "http://private.com/fire_worker.php";
    var id = userid;
    var vars = "userid="+id;
    hr.open("POST", url, true);
    // Set content type header information for sending url encoded variables in the request
    hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    // Access the onreadystatechange event for the XMLHttpRequest object
    hr.onreadystatechange = function() {
        if(hr.readyState == 4 && hr.status == 200) {
            var return_data = hr.responseText;
            document.getElementById('tellme').innerHTML = return_data;
        }
    }
    // Send the data to PHP now... and wait for response to update the status div
    hr.send(vars); // Actually execute the request
    document.getElementById('tellme').innerHTML = "<div class='alert alert-info'>Please wait, Processing request...</div>";
}
</script>