Report.url

let reportURL = reportInstance.url

let options = {
  types: ['deprecation'],
  buffered: true
}

let observer = new ReportingObserver(function(reports, observer) {
  let firstReport = reports[0];
  // Log the URL of the document that generated the first report
  // e.g. "https://www.example.com/cats.html"
  console.log(firstReport.url);
}, options);