NDEFReadingEvent.message

let aMessage = NDEFReadingEvent.message;

const ndefReader = new NDEFReader();

  function read() {
    return new Promise((resolve, reject) => {
      const ctlr = new AbortController();
      ctlr.signal.onabort = reject;
      ndefReader.addEventListener("reading", event => {
        ctlr.abort();
        resolve(event);
      }, { once: true });
      ndefReader.scan({ signal: ctlr.signal }).catch(err => reject(err));
    });
  }

  read().then(({ serialNumber }) => {
    console.log(serialNumber);
  });