Non-root deployments: in-app URLs about router HOT 2 CLOSED

let isUrlAvailable;
let urlDocument, urlBase, urlAnchor;

function ensureUrlAvailableOrPolyfilled() {
  if (isUrlAvailable === undefined) {
    try {
      const url = new URL('b', 'http://a');
      url.pathname = 'c';
      isUrlAvailable = (url.href === 'http://a/c');
    } catch (e) {
      isUrlAvailable = false;
    }

    if (!isUrlAvailable) {
      // The URL constructor is not available in IE11. Polyfil it by creating an
      // HTMLAnchorElement in an in-memory HTML document.
      urlDocument = document.implementation.createHTMLDocument('url');
      urlBase = urlDocument.createElement('base');
      urlDocument.head.appendChild(urlBase);
      urlAnchor = urlDocument.createElement('a');

      if (!urlAnchor.origin) {
        // IE11: HTMLAnchorElement does not have the `origin` property
        Object.defineProperty(urlAnchor, 'origin', {
          get: () => {
            // IE11: on HTTP and HTTPS the default port is not included into
            // window.location.origin, so won't include it here either.
            const port = urlAnchor.port;
            const protocol = urlAnchor.protocol;
            const defaultHttp = protocol === 'http:' && port === '80';
            const defaultHttps = protocol === 'https:' && port === '443';
            const host = (defaultHttp || defaultHttps)
              ? urlAnchor.hostname
              : urlAnchor.host;
            return `${protocol}//${host}`;
          }
        });
      }
    }
  }
}

function resolveURL(path, base) {
  ensureUrlAvailableOrPolyfilled();
  if (isUrlAvailable) {
    return new URL(path, base);
  }

  urlBase.href = base;
  urlAnchor.href = path.replace(/ /g, '%20');
  return urlAnchor;
}