The message read-only property of the DeprecationReportBody interface returns a human-readable description of the deprecation. This typically matches the message a browser will display in its DevTools console regarding a deprecated feature.

A string.

In this example we create a new ReportingObserver to observe deprecation reports, then print the value of message to the console.

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

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