Function resolveRelativeUrlFallback_

src/url.js:573–599

(relativeUrlString, baseUrl)

 * @private @visibleForTesting
 */
export function resolveRelativeUrlFallback_(relativeUrlString, baseUrl) {
  baseUrl = urlAsLocation(baseUrl);
  relativeUrlString = relativeUrlString.replace(/\\/g, '/');
  const relativeUrl = parseUrlDeprecated(relativeUrlString);

  // Absolute URL.
  if (relativeUrlString.toLowerCase().startsWith(relativeUrl.protocol)) {
    return relativeUrl.href;
  }

  // Protocol-relative URL.
  if (relativeUrlString.startsWith('//')) {
    return baseUrl.protocol + relativeUrlString;
  }

  // Absolute path.
  if (relativeUrlString.startsWith('/')) {
    return baseUrl.origin + relativeUrlString;
  }

  // Relative path.
  return (
    baseUrl.origin +
    baseUrl.pathname.replace(/\/[^/]*$/, '/') +
    relativeUrlString
  );
}

/**
 * Add "__amp_source_origin" query parameter to the URL.