function importSystemJsExtras(){
  return System.import('systemjs.config.extras.js')
  .catch(function(reason) {
    console.log(
      'Warning: System.import could not load the optional "systemjs.config.extras.js". Did you omit it by accident? Continuing without it.'
    );
    console.log(reason);
  });
}
Optional SystemJS configuration extras. Keep going w/o it