changedetection.io/changedetectionio/content_fetchers/res/favicon-fetcher.js

async () => {
  const links = Array.from(document.querySelectorAll('link[rel~="apple-touch-icon"], link[rel~="icon"]'));
  const icons = links.map(link => {
      const sizesStr = link.getAttribute('sizes');
      let size = 0;
      if (sizesStr) {
          const [w] = sizesStr.split('x').map(Number);
          if (!isNaN(w)) size = w;
      } else {
          size = 16;
      }
      return {
          size,
          rel: link.getAttribute('rel'),
          href: link.href
      };
  });

  if (icons.length === 0) return null;

  icons.sort((a, b) => {
      const isAppleA = /apple-touch-icon/.test(a.rel);
      const isAppleB = /apple-touch-icon/.test(b.rel);
      if (isAppleA && !isAppleB) return -1;
      if (!isAppleA && isAppleB) return 1;
      return b.size - a.size;
  });

  // Set a timeout value in ms
  const timeoutMs = 2000;

  for (const icon of icons) {
    try {
      const controller = new AbortController();
      const timeout = setTimeout(() => controller.abort(), timeoutMs);

      const resp = await fetch(icon.href, {
        signal: controller.signal,
        redirect: 'follow'
      });

      clearTimeout(timeout);

      if (!resp.ok) {
        // skip 404, 500, etc.
        continue;
      }

      const blob = await resp.blob();

      // Convert to base64
      const reader = new FileReader();
      return await new Promise(resolve => {
        reader.onloadend = () => {
          resolve({
            url: icon.href,
            base64: reader.result.split(",")[1]
          });
        };
        reader.readAsDataURL(blob);
      });

    } catch (e) {
      // fetch error, timeout, or abort
      continue;
    }
  }

  return null;
}