only show the scroll top top of activity feed button when the user has scroll...

only show the scroll top top of activity feed button when the user has scroll passed the top of the window

opentech/static_src/src/javascript/main.js

@@ -50,6 +50,11 @@ import Tabs from './components/tabs';
             $('.js-activity-feed').removeClass('is-open');
         });
 
+        // Show scroll to top of activity feed button on scroll
+        $('.js-activity-feed').on('scroll', function() {
+            $(this).scrollTop() === 0 ? $('.js-to-top').removeClass('is-visible') : $('.js-to-top').addClass('is-visible');
+        });
+
         // Scroll to the top of the activity feed
         $('.js-to-top').click(() => $('.js-activity-feed').animate({ scrollTop: 0 }, 250));
     });