What will be the output of this code snippet?

What will be the output of this code snippet?

class Mediator {
  notify(sender, event) {
    if (event === 'start') {
      console.log(sender + ' started');
    } else {
      console.log('Unknown event');
    }
  }
}
const mediator = new Mediator();
mediator.notify('ComponentX', 'stop');