Extract mounting of multiple boards switcher (EE-port)

app/assets/javascripts/boards/index.js

 import $ from 'jquery';
 import Vue from 'vue';
 
+import mountMultipleBoardsSwitcher from 'ee_else_ce/boards/mount_multiple_boards_switcher';
 import Flash from '~/flash';
 import { s__, __ } from '~/locale';
 import './models/label';
@@ -30,7 +31,6 @@ import 'ee/boards/models/list';
 import 'ee/boards/models/issue';
 import 'ee/boards/models/project';
 import BoardService from 'ee/boards/services/board_service';
-import BoardsSelector from 'ee/boards/components/boards_selector.vue';
 import collapseIcon from 'ee/boards/icons/fullscreen_collapse.svg';
 import expandIcon from 'ee/boards/icons/fullscreen_expand.svg';
 import tooltip from '~/vue_shared/directives/tooltip';
@@ -381,34 +381,5 @@ export default () => {
     `,
   });
 
-  const boardsSwitcherElement = document.getElementById('js-multiple-boards-switcher');
-  // eslint-disable-next-line no-new
-  new Vue({
-    el: boardsSwitcherElement,
-    components: {
-      BoardsSelector,
-    },
-    data() {
-      const { dataset } = boardsSwitcherElement;
-
-      const boardsSelectorProps = {
-        ...dataset,
-        currentBoard: JSON.parse(dataset.currentBoard),
-        hasMissingBoards: parseBoolean(dataset.hasMissingBoards),
-        canAdminBoard: parseBoolean(dataset.canAdminBoard),
-        multipleIssueBoardsAvailable: parseBoolean(dataset.multipleIssueBoardsAvailable),
-        projectId: Number(dataset.projectId),
-        groupId: Number(dataset.groupId),
-        scopedIssueBoardFeatureEnabled: parseBoolean(dataset.scopedIssueBoardFeatureEnabled),
-        weights: JSON.parse(dataset.weights),
-      };
-
-      return { boardsSelectorProps };
-    },
-    render(createElement) {
-      return createElement(BoardsSelector, {
-        props: this.boardsSelectorProps,
-      });
-    },
-  });
+  mountMultipleBoardsSwitcher();
 };

app/assets/javascripts/boards/mount_multiple_boards_switcher.js

+// this will be moved from EE to CE as part of https://gitlab.com/gitlab-org/gitlab-ce/issues/53811
+export default () => {};

ee/app/assets/javascripts/boards/mount_multiple_boards_switcher.js

+import Vue from 'vue';
+import { parseBoolean } from '~/lib/utils/common_utils';
+import BoardsSelector from 'ee/boards/components/boards_selector.vue';
+
+export default () => {
+  const boardsSwitcherElement = document.getElementById('js-multiple-boards-switcher');
+  return new Vue({
+    el: boardsSwitcherElement,
+    components: {
+      BoardsSelector,
+    },
+    data() {
+      const { dataset } = boardsSwitcherElement;
+
+      const boardsSelectorProps = {
+        ...dataset,
+        currentBoard: JSON.parse(dataset.currentBoard),
+        hasMissingBoards: parseBoolean(dataset.hasMissingBoards),
+        canAdminBoard: parseBoolean(dataset.canAdminBoard),
+        multipleIssueBoardsAvailable: parseBoolean(dataset.multipleIssueBoardsAvailable),
+        projectId: Number(dataset.projectId),
+        groupId: Number(dataset.groupId),
+        scopedIssueBoardFeatureEnabled: parseBoolean(dataset.scopedIssueBoardFeatureEnabled),
+        weights: JSON.parse(dataset.weights),
+      };
+
+      return { boardsSelectorProps };
+    },
+    render(createElement) {
+      return createElement(BoardsSelector, {
+        props: this.boardsSelectorProps,
+      });
+    },
+  });
+};