Cleaner global variable in JS

templates/feedbackform.html

@@ -73,7 +73,6 @@
 <script type="text/javascript">
     var call = JSON.parse('{{ @call | raw }}');
     var call_url = call['data']['url'];
-    var interval;
     function normalize_phone(phone) {
         if (phone.startsWith('+')) {
             return phone.replace('+', '00');
@@ -146,7 +145,7 @@
             $('#step5').removeClass('green').removeClass('outline_green').addClass('red');
             $('#step6').removeClass('green').removeClass('outline_green').addClass('red');
             $('#callee').removeClass('green').removeClass('outline_green').addClass('red');
-            clearInterval(interval);
+            clearInterval(window.interval);
         }
         console.log(call_state[0]);
     };
@@ -162,6 +161,6 @@
     };
     $(document).ready(function() {
         update_call(call);
-        interval = window.setInterval(fetch, 3000);
+        var window.interval = window.setInterval(fetch, 3000);
     });
 </script>