ตรวจ hreflang ระหว่างหน้าเวอร์ชันภาษา

(async () => {
  const MAX_VARIANTS = 30;
  const deadline = Date.now() + 30000;
  const currentCanonical = new URL(document.querySelector('link[rel="canonical"]')?.href || location.href, location.href).href;
  const tags = [...document.querySelectorAll('link[rel="alternate"][hreflang][href]')].slice(0, MAX_VARIANTS);
  const rows = [];
  for (const tag of tags) {
    const target = new URL(tag.href, location.href);
    const item = { language: tag.hreflang, url: target.href, sameOrigin: target.origin === location.origin, reciprocal: 'not checked' };
    if (item.sameOrigin) {
      if (Date.now() >= deadline) { item.reciprocal = 'skipped: 30-second runtime limit'; rows.push(item); continue; }
      const controller = new AbortController();
      const timer = setTimeout(() => controller.abort(), Math.min(5000, deadline - Date.now()));
      try {
        const response = await fetch(target.href, { credentials: 'omit', redirect: 'follow', signal: controller.signal });
        if (!response.ok || new URL(response.url).origin !== location.origin) throw new Error('HTTP ' + response.status + ' or cross-origin redirect');
        const doc = new DOMParser().parseFromString(await response.text(), 'text/html');
        const reciprocal = [...doc.querySelectorAll('link[rel="alternate"][hreflang][href]')].some((link) => {
          try { return new URL(link.href, target.href).href === currentCanonical; } catch { return false; }
        });
        item.reciprocal = reciprocal ? 'yes' : 'missing';
      } catch (error) { item.reciprocal = error.name === 'AbortError' ? 'timeout' : 'could not check'; }
      finally { clearTimeout(timer); }
    }
    rows.push(item);
  }
  console.table(rows);
  console.info('Current canonical:', currentCanonical, '· hreflang variants found:', tags.length);
  if (Date.now() >= deadline) console.warn('The 30-second runtime limit was reached; remaining links were not checked.');
  if (tags.length >= MAX_VARIANTS) console.warn('Only the first ' + MAX_VARIANTS + ' language variants were checked.');
  if (!tags.length) console.warn('No link rel=\"alternate\" hreflang entries were found.');
  console.info('Cross-origin and inaccessible pages are not fetched. A “missing” reciprocal link may also result from a canonical URL variant or redirect; review it manually.');
})();

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