refactor SigninTabsMemoizer class to ES module syntax

app/assets/javascripts/dispatcher.js

 /* eslint-disable func-names, space-before-function-paren, no-var, prefer-arrow-callback, wrap-iife, no-shadow, consistent-return, one-var, one-var-declaration-per-line, camelcase, default-case, no-new, quotes, no-duplicate-case, no-case-declarations, no-fallthrough, max-len */
-/* global ActiveTabMemoizer */
 /* global ShortcutsNavigation */
 /* global IssuableIndex */
 /* global ShortcutsIssuable */
@@ -50,6 +49,7 @@ import UsersSelect from './users_select';
 import RefSelectDropdown from './ref_select_dropdown';
 import GfmAutoComplete from './gfm_auto_complete';
 import ShortcutsBlob from './shortcuts_blob';
+import SigninTabsMemoizer from './signin_tabs_memoizer';
 import Star from './star';
 import Todos from './todos';
 import TreeView from './tree';
@@ -131,7 +131,7 @@ import OAuthRememberMe from './oauth_remember_me';
           break;
         case 'sessions:new':
           new UsernameValidator();
-          new ActiveTabMemoizer();
+          new SigninTabsMemoizer();
           new OAuthRememberMe({ container: $(".omniauth-container") }).bindEvents();
           break;
         case 'projects:boards:show':

app/assets/javascripts/main.js

@@ -143,7 +143,6 @@ import './render_math';
 import './right_sidebar';
 import './search';
 import './search_autocomplete';
-import './signin_tabs_memoizer';
 import './smart_interval';
 import './snippets_list';
 import './star';

app/assets/javascripts/signin_tabs_memoizer.js

@@ -6,7 +6,7 @@ import AccessorUtilities from './lib/utils/accessor';
  * Memorize the last selected tab after reloading a page.
  * Does that setting the current selected tab in the localStorage
  */
-class ActiveTabMemoizer {
+export default class SigninTabsMemoizer {
   constructor({ currentTabKey = 'current_signin_tab', tabSelector = 'ul.nav-tabs' } = {}) {
     this.currentTabKey = currentTabKey;
     this.tabSelector = tabSelector;
@@ -51,5 +51,3 @@ class ActiveTabMemoizer {
     return window.localStorage.getItem(this.currentTabKey);
   }
 }
-
-window.ActiveTabMemoizer = ActiveTabMemoizer;

spec/javascripts/signin_tabs_memoizer_spec.js

 import AccessorUtilities from '~/lib/utils/accessor';
+import SigninTabsMemoizer from '~/signin_tabs_memoizer';
 
-import '~/signin_tabs_memoizer';
-
-((global) => {
+(() => {
   describe('SigninTabsMemoizer', () => {
     const fixtureTemplate = 'static/signin_tabs.html.raw';
     const tabSelector = 'ul.nav-tabs';
@@ -10,7 +9,7 @@ import '~/signin_tabs_memoizer';
     let memo;
 
     function createMemoizer() {
-      memo = new global.ActiveTabMemoizer({
+      memo = new SigninTabsMemoizer({
         currentTabKey,
         tabSelector,
       });
@@ -78,7 +77,7 @@ import '~/signin_tabs_memoizer';
         beforeEach(function () {
           memo.isLocalStorageAvailable = false;
 
-          global.ActiveTabMemoizer.prototype.saveData.call(memo);
+          SigninTabsMemoizer.prototype.saveData.call(memo);
         });
 
         it('should not call .setItem', () => {
@@ -92,7 +91,7 @@ import '~/signin_tabs_memoizer';
         beforeEach(function () {
           memo.isLocalStorageAvailable = true;
 
-          global.ActiveTabMemoizer.prototype.saveData.call(memo, value);
+          SigninTabsMemoizer.prototype.saveData.call(memo, value);
         });
 
         it('should call .setItem', () => {
@@ -117,7 +116,7 @@ import '~/signin_tabs_memoizer';
         beforeEach(function () {
           memo.isLocalStorageAvailable = false;
 
-          readData = global.ActiveTabMemoizer.prototype.readData.call(memo);
+          readData = SigninTabsMemoizer.prototype.readData.call(memo);
         });
 
         it('should not call .getItem and should return `null`', () => {
@@ -130,7 +129,7 @@ import '~/signin_tabs_memoizer';
         beforeEach(function () {
           memo.isLocalStorageAvailable = true;
 
-          readData = global.ActiveTabMemoizer.prototype.readData.call(memo);
+          readData = SigninTabsMemoizer.prototype.readData.call(memo);
         });
 
         it('should call .getItem and return the localStorage value', () => {
@@ -140,4 +139,4 @@ import '~/signin_tabs_memoizer';
       });
     });
   });
-})(window);
+})();