Guard class

Provides functionality to block pages being loaded. Generally it's cleaner to not to use this class, and just use logic within the route map to return NotFound or Redirect, like this:

 '/protected-route': (route) {
   if (!isLoggedIn()) return Redirect('/login');
   if (!canUserAccessPage) return Redirect('/no-access');
   return ProtectedPage();
 }

If canNavigate returns true, the page returned by builder is shown.

If it returns false, the onNavigationFailed function is called. This can either return a new page, or return Redirect to go to a different path.

If no onNavigationFailed is provided, the default behavior is to redirect to the router's default path.