--- jsLoader.php.orig	2017-09-03 13:27:09.118746062 +0000
+++ jsLoader.php	2017-09-03 13:40:45.320446601 +0000
@@ -306,8 +306,8 @@
 }
 
 $jsLength = strlen($js);
-$etag = md5($jsLength);
-if (isset($_SERVER['HTTP_IF_NONE_MATCH']) && $_SERVER['HTTP_IF_NONE_MATCH'] == $etag) {
+$etag = '"'.md5($jsLength).'"';
+if (isset($_SERVER['HTTP_IF_NONE_MATCH']) && ($_SERVER['HTTP_IF_NONE_MATCH'] == $etag || $_SERVER['HTTP_IF_NONE_MATCH'] == 'W/'.$etag)) {
    header('HTTP/1.1 304 Not Modified');
    header('ETag: '.$etag);
    exit;