fix some code style issues according to feedback

app/assets/javascripts/activities.js.es6

@@ -5,9 +5,9 @@
   class Activities {
     constructor() {
       Pager.init(20, true, false, this.updateTooltips);
-      $('.event-filter-link').on('click', (event) => {
-        event.preventDefault();
-        this.toggleFilter($(event.currentTarget));
+      $('.event-filter-link').on('click', (e) => {
+        e.preventDefault();
+        this.toggleFilter(e.currentTarget);
         this.reloadActivities();
       });
     }
@@ -22,12 +22,13 @@
     }
 
     toggleFilter(sender) {
-      const filter = sender.attr('id').split('_')[0];
+      const $sender = $(sender);
+      const filter = $sender.attr('id').split('_')[0];
 
       $('.event-filter .active').removeClass('active');
       Cookies.set('event_filter', filter);
 
-      sender.closest('li').toggleClass('active');
+      $sender.closest('li').toggleClass('active');
     }
   }
 

app/assets/javascripts/pager.js.es6

 (() => {
+  const ENDLESS_SCROLL_BOTTOM_PX = 400;
+  const ENDLESS_SCROLL_FIRE_DELAY_MS = 1000;
+
   const Pager = {
     init(limit = 0, preload = false, disable = false, callback = $.noop) {
       this.limit = limit;
+      this.offset = this.limit;
       this.disable = disable;
       this.callback = callback;
       this.loading = $('.loading').first();
       if (preload) {
         this.offset = 0;
         this.getOld();
-      } else {
-        this.offset = this.limit;
       }
       this.initLoadMore();
     },
@@ -20,19 +22,19 @@
         type: 'GET',
         url: $('.content_list').data('href') || window.location.href,
         data: `limit=${this.limit}&offset=${this.offset}`,
+        dataType: 'json',
         error: () => this.loading.hide(),
         success: (data) => {
           this.append(data.count, data.html);
           this.callback();
 
           // keep loading until we've filled the viewport height
-          if (data.count > 0 && !this.isScrollable()) {
+          if (!this.disable && !this.isScrollable()) {
             this.getOld();
           } else {
             this.loading.hide();
           }
         },
-        dataType: 'json',
       });
     },
 
@@ -46,14 +48,15 @@
     },
 
     isScrollable() {
-      return $(document).height() > $(window).height() + $(window).scrollTop() + 400;
+      const $w = $(window);
+      return $(document).height() > $w.height() + $w.scrollTop() + ENDLESS_SCROLL_BOTTOM_PX;
     },
 
     initLoadMore() {
       $(document).unbind('scroll');
       $(document).endlessScroll({
-        bottomPixels: 400,
-        fireDelay: 1000,
+        bottomPixels: ENDLESS_SCROLL_BOTTOM_PX,
+        fireDelay: ENDLESS_SCROLL_FIRE_DELAY_MS,
         fireOnce: true,
         ceaseFire: () => this.disable === true,
         callback: () => {