convert Autosave into pure es module and remove global export

app/assets/javascripts/autosave.js

-/* eslint-disable func-names, space-before-function-paren, wrap-iife, no-param-reassign, quotes, prefer-template, no-var, one-var, no-unused-vars, one-var-declaration-per-line, no-void, consistent-return, no-empty, max-len */
+/* eslint-disable no-param-reassign, prefer-template, no-var, no-void, consistent-return */
+
 import AccessorUtilities from './lib/utils/accessor';
 
-window.Autosave = (function() {
-  function Autosave(field, key, resource) {
+export default class Autosave {
+  constructor(field, key, resource) {
     this.field = field;
     this.isLocalStorageAvailable = AccessorUtilities.isLocalStorageAccessSafe();
     this.resource = resource;
@@ -12,14 +13,10 @@ window.Autosave = (function() {
     this.key = 'autosave/' + key;
     this.field.data('autosave', this);
     this.restore();
-    this.field.on('input', (function(_this) {
-      return function() {
-        return _this.save();
-      };
-    })(this));
+    this.field.on('input', () => this.save());
   }
 
-  Autosave.prototype.restore = function() {
+  restore() {
     var text;
 
     if (!this.isLocalStorageAvailable) return;
@@ -40,9 +37,9 @@ window.Autosave = (function() {
         field.dispatchEvent(event);
       }
     }
-  };
+  }
 
-  Autosave.prototype.save = function() {
+  save() {
     var text;
     text = this.field.val();
 
@@ -51,15 +48,13 @@ window.Autosave = (function() {
     }
 
     return this.reset();
-  };
+  }
 
-  Autosave.prototype.reset = function() {
+  reset() {
     if (!this.isLocalStorageAvailable) return;
 
     return window.localStorage.removeItem(this.key);
-  };
-
-  return Autosave;
-})();
+  }
+}
 
-export default window.Autosave;
+window.Autosave = Autosave;

app/assets/javascripts/issuable_form.js

 /* eslint-disable func-names, space-before-function-paren, no-var, prefer-rest-params, wrap-iife, no-use-before-define, no-useless-escape, no-new, quotes, object-shorthand, no-unused-vars, comma-dangle, no-alert, consistent-return, no-else-return, prefer-template, one-var, one-var-declaration-per-line, curly, max-len */
 /* global GitLab */
-/* global Autosave */
 /* global GroupsSelect */
 
 import Pikaday from 'pikaday';
+import Autosave from './autosave';
 import UsersSelect from './users_select';
 import GfmAutoComplete from './gfm_auto_complete';
 import ZenMode from './zen_mode';

app/assets/javascripts/notes.js

@@ -5,7 +5,7 @@ default-case, prefer-template, consistent-return, no-alert, no-return-assign,
 no-param-reassign, prefer-arrow-callback, no-else-return, comma-dangle, no-new,
 brace-style, no-lonely-if, vars-on-top, no-unused-vars, no-sequences, no-shadow,
 newline-per-chained-call, no-useless-escape, class-methods-use-this */
-/* global Autosave */
+
 /* global ResolveService */
 /* global mrRefreshWidgetUrl */
 
@@ -21,7 +21,7 @@ import Flash from './flash';
 import CommentTypeToggle from './comment_type_toggle';
 import GLForm from './gl_form';
 import loadAwardsHandler from './awards_handler';
-import './autosave';
+import Autosave from './autosave';
 import './dropzone_input';
 import TaskList from './task_list';
 import { ajaxPost, isInViewport, getPagePath, scrollToElement, isMetaKey } from './lib/utils/common_utils';

app/assets/javascripts/notes/components/issue_comment_form.vue

 <script>
-  /* global Autosave */
   import { mapActions, mapGetters } from 'vuex';
   import _ from 'underscore';
   import autosize from 'vendor/autosize';
   import Flash from '../../flash';
-  import '../../autosave';
+  import Autosave from '../../autosave';
   import TaskList from '../../task_list';
   import * as constants from '../constants';
   import eventHub from '../event_hub';

app/assets/javascripts/notes/mixins/autosave.js

-/* globals Autosave */
-import '../../autosave';
+import Autosave from '../../autosave';
 
 export default {
   methods: {