FEATURE: add 'navigation-categories' class on 'body' when visiting /categories

app/assets/javascripts/discourse/views/discovery-categories.js.es6

@@ -1,11 +1,16 @@
 import UrlRefresh from 'discourse/mixins/url-refresh';
+import { on } from 'ember-addons/ember-computed-decorators';
+
+const CATEGORIES_LIST_BODY_CLASS = "categories-list";
 
 export default Ember.View.extend(UrlRefresh, {
-  _addBodyClass: function() {
-    $('body').addClass('categories-list');
-  }.on('didInsertElement'),
+  @on("didInsertElement")
+  addBodyClass() {
+    $('body').addClass(CATEGORIES_LIST_BODY_CLASS);
+  },
 
-  _removeBodyClass: function() {
-    $('body').removeClass('categories-list');
-  }.on('willDestroyElement')
+  @on("willDestroyElement")
+  removeBodyClass() {
+    $('body').removeClass(CATEGORIES_LIST_BODY_CLASS);
+  },
 });

app/assets/javascripts/discourse/views/navigation-categories.js.es6

@@ -0,0 +1,15 @@
+import { on } from 'ember-addons/ember-computed-decorators';
+
+const CATEGORIES_BODY_CLASS = "navigation-categories";
+
+export default Ember.View.extend({
+  @on("didInsertElement")
+  addBodyClass() {
+    $('body').addClass(CATEGORIES_BODY_CLASS);
+  },
+
+  @on("willDestroyElement")
+  removeBodyClass() {
+    $('body').removeClass(CATEGORIES_BODY_CLASS);
+  },
+});

app/assets/javascripts/discourse/views/navigation-category.js.es6

@@ -1,5 +1,5 @@
 import AddCategoryClass from 'discourse/mixins/add-category-class';
 
-export default Em.View.extend(AddCategoryClass, {
-  categoryFullSlug: Em.computed.alias('controller.category.fullSlug')
+export default Ember.View.extend(AddCategoryClass, {
+  categoryFullSlug: Ember.computed.alias('controller.category.fullSlug')
 });