Performance Improvements for the Epic View

StartupJS Loading of Epic Discussions
Better Init
Removed double rendering

app/assets/javascripts/issue_show/components/app.vue

@@ -3,6 +3,7 @@ import { GlIcon, GlIntersectionObserver } from '@gitlab/ui';
 import Visibility from 'visibilityjs';
 import { __, s__, sprintf } from '~/locale';
 import { deprecatedCreateFlash as createFlash } from '~/flash';
+import { sanitize } from '~/lib/dompurify';
 import { visitUrl } from '~/lib/utils/url_utility';
 import Poll from '~/lib/utils/poll';
 import eventHub from '../event_hub';
@@ -178,7 +179,7 @@ export default {
     const store = new Store({
       titleHtml: this.initialTitleHtml,
       titleText: this.initialTitleText,
-      descriptionHtml: this.initialDescriptionHtml,
+      descriptionHtml: sanitize(this.initialDescriptionHtml),
       descriptionText: this.initialDescriptionText,
       updatedAt: this.updatedAt,
       updatedByName: this.updatedByName,

ee/app/assets/javascripts/pages/groups/epics/show/index.js

@@ -5,8 +5,11 @@ import ZenMode from '~/zen_mode';
 import '~/notes/index';
 import loadAwardsHandler from '~/awards_handler';
 
-new ZenMode(); // eslint-disable-line no-new
 initEpicApp();
-new ShortcutsEpic(); // eslint-disable-line no-new
-new EpicTabs(); // eslint-disable-line no-new
-loadAwardsHandler();
+
+requestIdleCallback(() => {
+  new EpicTabs(); // eslint-disable-line no-new
+  new ShortcutsEpic(); // eslint-disable-line no-new
+  loadAwardsHandler();
+  new ZenMode(); // eslint-disable-line no-new
+});

ee/app/views/groups/epics/show.html.haml

@@ -19,6 +19,8 @@
 - add_page_specific_style 'page_bundles/epics'
 - add_page_specific_style 'page_bundles/roadmap'
 
+- add_page_startup_api_call discussions_path(@epic)
+
 #epic-app-root{ data: epic_show_app_data(@epic),
   'data-allow-sub-epics' => allow_sub_epics }