インタラクションとソフト ナビゲーションのペイントのタイミングを測定する

/**
 * Observes contentful paints caused by user interactions and invokes a callback
 * whenever an interaction produces a larger contentful paint.
 *
 * @param {(entry: PerformanceEntry) => void} onInteractionPaint
 */
export function observeInteractionPaints(onInteractionPaint) {
  // Feature-detect support before calling observe() so unsupported browsers
  // do not throw or log console warnings.
  if (
    typeof PerformanceObserver === 'undefined' ||
    !PerformanceObserver.supportedEntryTypes?.includes('interaction-contentful-paint')
  ) {
    return null;
  }

  const observer = new PerformanceObserver((list) => {
    for (const entry of list.getEntries()) {
      // entry.duration is already calculated as (entry.presentationTime - entry.startTime),
      // giving the total time from the user interaction to this contentful paint.
      onInteractionPaint(entry);
    }
  });

  // MANDATORY: Pass buffered: true to capture interaction paints that occurred
  // before this observer was registered.
  observer.observe({ type: 'interaction-contentful-paint', buffered: true });
  return observer;
}

/**
 * Tracks FCP and LCP for each client-side soft navigation and reports finalized
 * route metrics when the user navigates to a new route or hides the page.
 *
 * @param {(report: {
 *   url: string,
 *   navigationId: number,
 *   interactionId: number,
 *   fcpDuration: number,
 *   lcpDuration: number | null,
 *   lcpElement: Element | null,
 *   lcpSize: number | null
 * }) => void} onSoftNavReport
 */
export function trackSoftNavigationLCP(onSoftNavReport) {
  const supported =
    typeof PerformanceObserver !== 'undefined' &&
    PerformanceObserver.supportedEntryTypes?.includes('soft-navigation') &&
    PerformanceObserver.supportedEntryTypes?.includes('interaction-contentful-paint');

  if (!supported) {
    return null;
  }

  let activeSoftNav = null;
  let activeLcpEntry = null;

  function finalizeCurrentSoftNav() {
    if (!activeSoftNav) return;

    onSoftNavReport({
      // activeSoftNav.name holds the destination URL of the soft navigation.
      url: activeSoftNav.name,
      navigationId: activeSoftNav.navigationId,
      interactionId: activeSoftNav.interactionId,
      // activeSoftNav.duration is (activeSoftNav.presentationTime - activeSoftNav.startTime),
      // which represents First Contentful Paint (FCP) relative to interaction start.
      fcpDuration: activeSoftNav.duration,
      // activeLcpEntry.duration is (activeLcpEntry.presentationTime - activeSoftNav.startTime),
      // representing the soft navigation's LCP duration relative to interaction start.
      lcpDuration: activeLcpEntry ? activeLcpEntry.duration : null,
      lcpElement: activeLcpEntry?.largestContentfulPaint?.element ?? null,
      lcpSize: activeLcpEntry?.largestContentfulPaint?.size ?? null,
    });

    activeSoftNav = null;
    activeLcpEntry = null;
  }

  const softNavObserver = new PerformanceObserver((list) => {
    for (const softNavEntry of list.getEntries()) {
      // Finalize the previous route's metrics before resetting state for the new route.
      finalizeCurrentSoftNav();

      activeSoftNav = softNavEntry;
      // MANDATORY: Seed the LCP candidate with getLargestInteractionContentfulPaint()
      // to capture any attributed contentful paints that occurred before the URL updated.
      activeLcpEntry = softNavEntry.getLargestInteractionContentfulPaint();
    }
  });

  const icpObserver = new PerformanceObserver((list) => {
    for (const icpEntry of list.getEntries()) {
      // MANDATORY: Match by interactionId (not navigationId) so only paints caused
      // by the soft navigation's initiating interaction update the route's LCP.
      if (activeSoftNav && icpEntry.interactionId === activeSoftNav.interactionId) {
        activeLcpEntry = icpEntry;
      }
    }
  });

  softNavObserver.observe({ type: 'soft-navigation', buffered: true });
  icpObserver.observe({ type: 'interaction-contentful-paint', buffered: true });

  // Finalize the active route's LCP when the page is backgrounded or unloaded.
  document.addEventListener('visibilitychange', () => {
    if (document.visibilityState === 'hidden') {
      finalizeCurrentSoftNav();
    }
  });

  return { softNavObserver, icpObserver, finalizeCurrentSoftNav };
}

import { onLCP, onFCP, onCLS, onINP } from 'web-vitals';

function sendToAnalytics(metric) {
  // Example-only endpoint; replace with your real telemetry URL.
  navigator.sendBeacon(
    '/analytics',
    JSON.stringify({
      name: metric.name,
      value: metric.value,
      navigationType: metric.navigationType,
      navigationURL: metric.navigationURL,
    }),
  );
}

// Pass { reportSoftNavs: true } to report metrics per soft navigation in addition
// to the initial hard navigation.
onLCP(sendToAnalytics, { reportSoftNavs: true });
onFCP(sendToAnalytics, { reportSoftNavs: true });
onCLS(sendToAnalytics, { reportSoftNavs: true });
onINP(sendToAnalytics, { reportSoftNavs: true });