// Catch errors since some browsers throw when using the new `type` option.

// https://bugs.webkit.org/show_bug.cgi?id=209216

try {

  // Create the performance observer.

  const po = new PerformanceObserver((list) => {

    for (const entry of list.getEntries()) {

      // If transferSize is 0, the resource was fulfilled via the cache.

      console.log('Time to first byte', entry.responseStart);

    }

  });

  // Start listening for `navigation` entries to be dispatched.

  po.observe({type: 'navigation', buffered: true});

} catch (e) {

  // Do nothing if the browser doesn't support this API.

}

// Catch errors since some browsers throw when using the new `type` option.

// https://bugs.webkit.org/show_bug.cgi?id=209216

try {

  // Create the performance observer.

  const po = new PerformanceObserver((list) => {

    for (const entry of list.getEntries()) {

      console.log('Service Worker startup time:',

          entry.responseStart - entry.workerStart);

    }

  });

  // Start listening for `navigation` entries to be dispatched.

  po.observe({type: 'navigation', buffered: true});

} catch (e) {

  // Do nothing if the browser doesn't support this API.

}