empty responseText sending a xmlhttprequest

Question

when I send the request the alert is blank. the files are uploaded fine, just no responsetext. Am I doing something wrong here?

var request = new XMLHttpRequest();

request.open('POST','upload.php');
request.setRequestHeader('Cache-Control','no-cache');
request.send(data);
alert(request.responseText);

and upload.php

if(!empty($_FILES['file'])){
foreach  ($_FILES['file']['name'] as $key => $name) {
if($_FILES['file']['error'][$key] == 0 && move_uploaded_file($_FILES['file']['tmp_name'][$key],"video/$name"))
    {
       $x = "1";
    }
        else
    {
      $x = "2";
    }
  }
}
   if ($x == "1"){echo "success";}
   if ($x == "2"){echo "failed";}

Answer 1

您已经处理了$x的输出，其值为1和2。如果根本没有设置$x怎么办？