Need help on using html library on flutter web

I want to get the location of the top window using the html library but it ends up getting an error when it was opened with an IFrame. This is my code

@override
  void initState() {
   url = html.window.top.location.toString();
    super.initState();
  }

i want the url becomes http://localhost:8000/folder1 (which is where the parent IFrames is located) but it ends up becomes "Instance of 'Minified:NC'" Did anyone have an experience using the html library? thanks