GA4 COOKIES PARSER

ga4CookieParser.js

/**
 * Parses GA4 cookies using a measurement ID without polluting the global namespace
 * @param {string} measurementId - GA4 measurement ID (e.g., 'G-XXXXXXXX')
 * @returns {Object|null} Parsed GA4 cookie data or null if cookies not found
 */
function parseGA4Cookies(measurementId) {
  function getCookieValue(name) {
    const match = document.cookie.match('(^|;)\\s*' + name + '\\s*=\\s*([^;]+)');
    return match ? match.pop() : null;
  }

  // Validate measurement ID
  if (!measurementId || typeof measurementId !== 'string') {
    console.error('Invalid measurement ID');
    return null;
  }

  // Extract ID suffix
  const parts = measurementId.split('-');
  if (parts.length !== 2 || !parts[1]) {
    console.error('Invalid measurement ID format. Expected: G-XXXXXXXX');
    return null;
  }
  const idSuffix = parts[1];
  
  // Get the cookies
  const gaCookie = getCookieValue('_ga');
  const ga4Cookie = getCookieValue(`_ga_${idSuffix}`);
  
  if (!ga4Cookie) {
    return null;
  }
  
  // Parse GA4 cookie
  const cookieParts = ga4Cookie.split('.');
  if (cookieParts.length < 6) {
    return null;
  }
  
  // Build result object
  const result = {
    measurementId: measurementId,
    streamType: cookieParts[0],
    hostnameSegments: parseInt(cookieParts[1], 10) || 0,
    sessionStartTimestamp: new Date(parseInt(cookieParts[2], 10) * 1000 || 0).toISOString(),
    sessionsCount: parseInt(cookieParts[3], 10) || 0,
    sessionEngaged: cookieParts[4] === '1',
    latestHitTimestamp: new Date(parseInt(cookieParts[5], 10) * 1000 || 0).toISOString()
  };
  
  // Add enhanced user ID if available
  if (cookieParts.length > 8 && cookieParts[8]) {
    result.enhancedUserId = isNaN(cookieParts[8]) ? cookieParts[8] : parseInt(cookieParts[8], 10);
  }
  
  // Extract client ID from _ga cookie if available
  if (gaCookie) {
    const match = gaCookie.match(/^[^.]*\.[^.]*\.(.*)$/);
    if (match && match[1]) {
      const clientId = match[1];
      result.clientId = clientId;
      
      const timestampPart = clientId.split('.')[1];
      if (timestampPart && !isNaN(timestampPart)) {
        result.firstVisitTimestamp = new Date(parseInt(timestampPart, 10) * 1000).toISOString();
      }
    }
  }
  
  return result;
}