I am getting an undefined variable

I am trying to retrieve a file name from the server of the file that has just been uploaded. The problem is that I am getting an undefine index on my php variable below:

 Undefined index: fileimagename in /web/stud/xxx/Mobile_app/QandATable.php on line 19
 

What I am trying to do is that user uploads the form which is done by the php script (imageupload.php), Now when uploading stops it uses the javascript function which is on a seperate page (QandATable.php, same page as the ) to display the message if upload is successful and this would append the name of the file uploaded.
So my question is how can I fix the undefined variable and how can I get the javascript function in the QandATable.php to retireve the file name from imageupload.php?

Below is code which consists the undefined variable and javascript function (QandATable.php):

            <?php
 session_start();
 
 $fileimagename = $_SESSION['fileimagename'];
 
 ?>
 
 <script type="text/javascript">
 
 function stopImageUpload(success){
 
      var fileimagename = <?php echo $fileimagename; ?>;
       var result = '';
       if (success == 1){
       result = '<span class="msg">The file was uploaded successfully!</span><br/><br/>';
          $('.listImage').append(fileimagename + '<br/>');
       }
       else {
    result = '<span class="emsg">There was an error during file upload!</span><br/><br/>';
       }
 
 return true
 };
 </script>
 

Below is php script which uploads the file into the server: (imageupload.php)

 <?php
 
     session_start();
 
     if (isset($_POST['fileimagename'])) {
 
     $_SESSION['fileimagename'] =  $_SESSION[' $_FILES['fileImage']['name']'];
 
     }
 
     if( file_exists("ImageFiles/".$_FILES['fileImage']['name'])) {
         $parts = explode(".",$_FILES['fileImage']['name']);
         $ext = array_pop($parts);
         $base = implode(".",$parts);
         $n = 2;
 
         while( file_exists("ImageFiles/".$base."_".$n.".".$ext)) $n++;
         $_FILES['fileImage']['name'] = $base."_".$n.".".$ext;
 
         move_uploaded_file($_FILES["fileImage"]["tmp_name"],
         "ImageFiles/" . $_FILES["fileImage"]["name"]);
         $result = 1;
 
     }
         else
           {
           move_uploaded_file($_FILES["fileImage"]["tmp_name"],
           "ImageFiles/" . $_FILES["fileImage"]["name"]);
           $result = 1;
 
           }
 
     ?>
 
     <script language="javascript" type="text/javascript">
 
 window.top.window.stopImageUpload(<?php echo $result;?>,'<?php echo $fileimagename;?>');
 
 </script>  
 

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