How to use the qz-tray.printers function in qz-tray

qz.security.setSignaturePromise(hash => {
  return (resolve, reject) => {
   fetch("/path/to/controller?request=" + hash, {cache: 'no-store', headers: {'Content-Type': 'text/plain'}})
    .then(wrapped => wrapped.text())
    .then(data => resolve(data))
    .catch(err => console.error(err));
   });
  };
 });
 */

qz.api.setSha256Type(data => sha256(data));
qz.api.setPromiseType(resolver => new Promise(resolver));

qz.websocket.connect()
 .then(qz.printers.getDefault)
 .then(printer => console.log("The default printer is: " + printer))
 .then(qz.websocket.disconnect)
 .catch(err => console.error(err));

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'QZ Tray AngularJS Signing';
}