InterventionReportBody.message

The message read-only property of the InterventionReportBody interface returns a human-readable description of the intervention, including information such as how the intervention could be avoided. This typically matches the message a browser will display in its DevTools console when an intervention is imposed, if one is available.

const options = {
  types: ["intervention"],
  buffered: true,
};

const observer = new ReportingObserver((reports, observer) => {
  const firstReport = reports[0];
  console.log(firstReport.type); // intervention
  console.log(firstReport.body.message);
}, options);