Add error message if loading fails

frontend/src/services/UserStatsService.ts

@@ -13,6 +13,14 @@ export default class UserStatsService {
   async getStats(): Promise<TableEntry[]> {
     return fetch(this.apiURL, this.requestInit)
       .then(res => { console.log(res); return res; })
-      .then(res => res.json())
+      .then(res => this.checkResponse(res))
+      .then(data => data.json())
+  }
+
+  private checkResponse(response: any): any {
+    if (!response.ok) {
+      throw Error(response.statusText);
+    }
+    return response;
   }
 }