use asButton() instead of custom JS code, fixes #2830

Closes #2830

Merge request studip/studip!1916

app/controllers/messages.php

@@ -718,7 +718,6 @@ class MessagesController extends AuthenticatedController {
     /* delete all sent or received messages */
     public function purge_action($sndrec)
     {
-        if (Request::isPost()) {
         CSRFProtection::verifyUnsafeRequest();
 
         $query = "SELECT message_id
@@ -741,7 +740,6 @@ class MessagesController extends AuthenticatedController {
             $this->redirect('messages/sent');
         }
     }
-    }
 
     protected function getMessages($received = true, $limit = 50, $offset = 0, $tag = null, $search = null)
     {
@@ -1009,8 +1007,8 @@ class MessagesController extends AuthenticatedController {
                     _('Nachrichten im Posteingang löschen'),
                     $this->url_for('messages/purge/rec'),
                     Icon::create('trash'),
-                    ['onclick' => 'return STUDIP.Dialog.confirmAsPost("' . $message . '", this.href);']
-                );
+                    ['data-confirm' => $message]
+                )->asButton();
             }
         } elseif ($action === 'sent') {
             if (MessageUser::countBySQL("snd_rec = 'snd' AND user_id = :id AND deleted != 1 LIMIT 1", ['id' => $GLOBALS['user']->id])) {