Better waitForAnimation end function (?). Maybe it was better before....

scripts/session_startup_animation.js

@@ -1,16 +1,13 @@
-function waitForAnimationEnd(elem, animationName)
+function waitForAnimationEnd(elem, animation_name)
 {
     return new Promise(resolve => {
-        function handleAnimationEnd(evt)
-        {
-            if (evt.animationName === animationName)
+        elem.onanimationend = (event) => {
+            if(event.animationName === animation_name)
             {
                 elem.onanimationend = null;
                 resolve();
             }
-        }
-
-        elem.onanimationend = handleAnimationEnd;
+        };
     });
 }