Make CSS selector related improvements to IssuableBulkUpdateSidebar.

app/assets/javascripts/issuable_bulk_update_sidebar.js

+const HIDDEN_CLASS = 'hidden';
+const DISABLED_CONTENT_CLASS = 'disabled-content';
+const SIDEBAR_EXPANDED_CLASS = 'right-sidebar-expanded';
 export default class IssuableBulkUpdateSidebar {
   constructor() {
@@ -35,7 +38,7 @@ export default class IssuableBulkUpdateSidebar {
   }
   prepForSubmit() {
-    this.$bulkEditSubmitBtn.prop('disabled', true);
+    this.$bulkEditSubmitBtn.disable();
     this.updateSelectedIssuableIds();
   }
@@ -59,41 +62,31 @@ export default class IssuableBulkUpdateSidebar {
   }
   toggleSidebarDisplay(show) {
-    const SIDEBAR_EXPANDED_CLASS = 'right-sidebar-expanded';
+    this.$page.toggleClass(SIDEBAR_EXPANDED_CLASS, show);
+    this.$sidebar.toggleClass(SIDEBAR_EXPANDED_CLASS, show);
     if (show) {
-      this.$page.addClass(SIDEBAR_EXPANDED_CLASS);
-      this.$sidebar.addClass(SIDEBAR_EXPANDED_CLASS).show();
+      this.$sidebar.show();
     } else {
-      this.$page.removeClass(SIDEBAR_EXPANDED_CLASS);
-      this.$sidebar.removeClass(SIDEBAR_EXPANDED_CLASS).hide();
+      this.$sidebar.hide();
     }
   }
   toggleBulkEditButtonDisabled(disable) {
-    this.$bulkUpdateEnableBtn.attr('disabled', disable);
+    if (disable) {
+      this.$bulkUpdateEnableBtn.disable();
+    } else {
+      this.$bulkUpdateEnableBtn.enable();
+    }
   }
   toggleCheckboxDisplay(show) {
-    const HIDDEN_CLASS = 'hidden';
-
-    if (show) {
-      this.$checkAllContainer.removeClass(HIDDEN_CLASS);
-      this.$issueChecks.removeClass(HIDDEN_CLASS);
-    } else {
-      this.$checkAllContainer.addClass(HIDDEN_CLASS);
-      this.$issueChecks.addClass(HIDDEN_CLASS);
-    }
+    this.$checkAllContainer.toggleClass(HIDDEN_CLASS, show);
+    this.$issueChecks.toggleClass(HIDDEN_CLASS, show);
   }
   toggleOtherFiltersDisabled(disable) {
-    const DISABLED_CONTENT_CLASS = 'disabled-content';
-
-    if (disable) {
-      this.$otherFilters.addClass(DISABLED_CONTENT_CLASS);
-    } else {
-      this.$otherFilters.removeClass(DISABLED_CONTENT_CLASS);
-    }
+    this.$otherFilters.toggleClass(DISABLED_CONTENT_CLASS, disable);
   }
   static getCheckedIssueIds() {
@@ -102,6 +95,7 @@ export default class IssuableBulkUpdateSidebar {
     if ($checkedIssues.length > 0) {
       return $.map($checkedIssues, value => $(value).data('id'));
     }
+
     return [];
   }
 }