Web-Vitals JS libraries

web vitals

<script type="module">
  // Load the web-vitals library from unpkg.com (or host locally):
  import {getFCP, getLCP, getCLS, getTTFB, getFID} from 'https://unpkg.com/web-vitals?module';
  
  function getSelector(node, maxLen = 100) {
    let sel = '';
    try {
      while (node && node.nodeType !== 9) {
        const part = node.id ? '#' + node.id : node.nodeName.toLowerCase() + (
          (node.className && node.className.length) ?
          '.' + Array.from(node.classList.values()).join('.') : '');
        if (sel.length + part.length > maxLen - 1) return sel || part;
        sel = sel ? part + '>' + sel : part;
        if (node.id) break;
        node = node.parentNode;
      }
    } catch (err) {
      // Do nothing...
    }
    return sel;
  }
  
  function getLargestLayoutShiftEntry(entries) {
    return entries.reduce((a, b) => a && a.value > b.value ? a : b);
  }
  
  function getLargestLayoutShiftSource(sources) {
    return sources.reduce((a, b) => {
      return a.node && a.previousRect.width * a.previousRect.height >
          b.previousRect.width * b.previousRect.height ? a : b;
    });
  }
  
  function wasFIDBeforeDCL(fidEntry) {
    const navEntry = performance.getEntriesByType('navigation')[0];
    return navEntry && fidEntry.startTime < navEntry.domContentLoadedEventStart;
  }
  
  function sendWebVitals() {
    function sendWebVitalsGAEvents({name, delta, id, entries}) {
      if ("function" == typeof ga) {
  
        let webVitalInfo = '(not set)';
  
        // Set a custom dimension for more info for any CVW breaches
        // In some cases there won't be any entries (e.g. if CLS is 0,
        // or for LCP after a bfcache restore), so we have to check first.
        if (entries.length) {
          if (name === 'LCP') {
             const lastEntry = entries[entries.length - 1];
             webVitalInfo =  getSelector(lastEntry.element);
          } else if (name === 'FID') {
            const firstEntry = entries[0];
            webVitalInfo = getSelector(firstEntry.target);
          } else if (name === 'CLS') {
             const largestEntry = getLargestLayoutShiftEntry(entries);
             if (largestEntry && largestEntry.sources) {
                const largestSource = getLargestLayoutShiftSource(largestEntry.sources);
                if (largestSource) {
                  webVitalInfo = getSelector(largestSource.node);
                }
             }
          }
        }
  
        ga('send', 'event', {
          eventCategory: 'Web Vitals',
          eventAction: name,
          // The `id` value will be unique to the current page load. When sending
          // multiple values from the same page (e.g. for CLS), Google Analytics can
          // compute a total by grouping on this ID (note: requires `eventLabel` to
          // be a dimension in your report).
          eventLabel: id,
          // Google Analytics metrics must be integers, so the value is rounded.
          // For CLS the value is first multiplied by 1000 for greater precision
          // (note: increase the multiplier for greater precision if needed).
          eventValue: Math.round(name === 'CLS' ? delta * 1000 : delta),
          // Use a non-interaction event to avoid affecting bounce rate.
          nonInteraction: true,
          // Use `sendBeacon()` if the browser supports it.
          transport: 'beacon',
  
          // OPTIONAL: any additional params or debug info here.
          // See: https://web.dev/debug-web-vitals-in-the-field/
          // dimension1: '...',
          // dimension2: '...',
          dimension2: webVitalInfo
          // ...
        });
      }
    }

    // Register function to send Core Web Vitals and other metrics as they become available
    getFCP(sendWebVitalsGAEvents);
    getLCP(sendWebVitalsGAEvents);
    getCLS(sendWebVitalsGAEvents);
    getTTFB(sendWebVitalsGAEvents);
    getFID(sendWebVitalsGAEvents);
  
  }
  
  sendWebVitals();
</script>