An example of Performance Observer reporting data to Google Analytics

performance-observer-ga.js

const observer = new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    // `name` will be either 'first-paint' or 'first-contentful-paint'.
    const metricName = entry.name;
    const time = Math.round(entry.startTime + entry.duration);

    ga('send', 'event', {
      eventCategory: 'Performance Metrics',
      eventAction: metricName,
      eventValue: time,
      nonInteraction: true,
    });
  }
});

// Start observing paint entries.
observer.observe({entryTypes: ['paint']});