diff --git a/templates/appointment.tera.html b/templates/appointment.tera.html
index 186ba54..e431d2c 100644
--- a/templates/appointment.tera.html
+++ b/templates/appointment.tera.html
@@ -30,10 +30,12 @@
 
 {% block scripts %}
     <script>
-        let iframe = document.querySelector("#iframe");
+        "use strict";
 
-        iframe.addEventListener('load', function() {
-            iframe.style.height = iframe.contentDocument.body.scrollHeight + 50 + 'px';
+        const iframe = document.querySelector("#iframe");
+
+        iframe.addEventListener("load", () => {
+            iframe.style.height = iframe.contentDocument.body.scrollHeight + 50 + "px";
         });
     </script>
 {% endblock %}