refactor(v2): mobile dropdown navbar: expand when subitem become active (#5168)

packages/docusaurus-theme-common/src/utils/useLocalPathname.ts

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import useDocusaurusContext from '@docusaurus/useDocusaurusContext';
+import {useLocation} from '@docusaurus/router';
+
+// Get the pathname of current route, without the optional site baseUrl
+// - /docs/myDoc => /docs/myDoc
+// - /baseUrl/docs/myDoc => /docs/myDoc
+export function useLocalPathname(): string {
+  const {
+    siteConfig: {baseUrl},
+  } = useDocusaurusContext();
+  const {pathname} = useLocation();
+  return pathname.replace(baseUrl, '/');
+}