Get top-most URL from within an iFrame. It either uses the referrer or the current location.

get-url.js

export default getUrl;

function getUrl(window) {
  const topMostWindow = getTopMostIframeWithReferrer(window);
  const { referrer } = topMostWindow.document;

  if (!isInIframe(window)) return window.location.href;

  // in Firefox it won't fill the referrer for friendly iframes
  if (referrer === '' && isParentFrameFriendly(topMostWindow)) {
    return topMostWindow.parent.location.href;
  }

  return referrer || '';
}

function getTopMostIframeWithReferrer(window) {
  if (isInIframe(window)) {
    if (isParentFrameFriendly(window) && !isParentFrameTop(window)) {
      return getTopMostIframeWithReferrer(window.parent);
    }
  }
  return window;
}

function isParentFrameFriendly(window) {
  try {
    return !!window.parent.document;
  } catch (e) {
    return false;
  }
}

function isParentFrameTop(window) {
  try {
    return window.parent === window.top;
  } catch (e) {
    return false;
  }
}

// taken from http://stackoverflow.com/questions/326069
function isInIframe(window) {
  try {
    return window.self !== window.top;
  } catch (e) {
    return true;
  }
}