const observer = new PerformanceObserver(
  (list, observer, options) => {
    for (const entry of list.getEntries()) {
      console.log(
        'Received entry with type',
        entry.entryType,
        'and name',
        entry.name,
        'that started at',
        entry.startTime,
        'and took',
        entry.duration,
        'ms',
      );
    }
  },
);

observer.observe({entryTypes: ['mark', 'measure']});