Optionally strip off the basename from the dashboard URL when

normalizing.

src/dashboard.tsx

@@ -1,6 +1,6 @@
 import { IFrame, MainAreaWidget, ToolbarButton } from '@jupyterlab/apputils';
 
-import { URLExt } from '@jupyterlab/coreutils';
+import { PageConfig, URLExt } from '@jupyterlab/coreutils';
 
 import { ServerConnection } from '@jupyterlab/services';
 
@@ -453,12 +453,25 @@ namespace Private {
   /**
    * Optionally remove a `status` route from a dashboard url.
    */
-  export function normalizeDashboardUrl(url: string): string {
-    if (url.endsWith('status')) {
-      return url.slice(0, -'status'.length);
+  export function normalizeDashboardUrl(url: string, baseUrl = ''): string {
+    if (URLExt.isLocal(url)) {
+      if (!baseUrl) {
+        baseUrl = PageConfig.getBaseUrl();
+      }
+      // If the path-portion of the baseUrl has been included,
+      // strip that off.
+      const tmp = new URL(baseUrl);
+      if (url.startsWith(tmp.pathname)) {
+        url = url.slice(tmp.pathname.length);
+      }
+      // Fully specify the local URL.
+      url = URLExt.join(baseUrl, url);
     }
-    if (url.endsWith('status/')) {
-      return url.slice(0, -'status/'.length);
+    // If 'status' has been included at the end, strip it.
+    if (url.endsWith('status')) {
+      url = url.slice(0, -'status'.length);
+    } else if (url.endsWith('status/')) {
+      url = url.slice(0, -'status/'.length);
     }
     return url;
   }
@@ -470,7 +483,7 @@ namespace Private {
     url: string,
     settings: ServerConnection.ISettings
   ): Promise<boolean> {
-    url = normalizeDashboardUrl(url);
+    url = normalizeDashboardUrl(url, settings.baseUrl);
 
     // If this is a url that we are proxying under the notebook server,
     // it is easier to check for a valid dashboard.