code: function isActive(_ref, indexOnly, currentLocation, routes, params) {
    var pathname = _ref.pathname;
    var query = _ref.query;
  
    if (currentLocation == null) return false;
  
    // TODO: This is a bit ugly. It keeps around support for treating pathnames
    // without preceding slashes as absolute paths, but possibly also works
    // around the same quirks with basenames as in matchRoutes.
    if (pathname.charAt(0) !== '/') {
      pathname = '/' + pathname;
    }
  
    if (!pathIsActive(pathname, currentLocation.pathname)) {
      // The path check is necessary and sufficient for indexOnly, but otherwise
      // we still need to check the routes.
      if (indexOnly || !routeIsActive(pathname, routes, params)) {
        return false;
      }
    }
  
    return queryIsActive(query, currentLocation.query);
  }
docs: Returns true if a <Link> to the given pathname/query combination is
  currently active.