environment.js

import RelayDefaultMissingFieldHandlers from 'relay-runtime/lib/handlers/RelayDefaultMissingFieldHandlers';
import missingHandlerByRefConcreteTypeField from './missingHandlerByRefConcreteTypeField';

const store = new Store(new RecordSource());
const network = Network.create(fetchQuery);

const environment = new Environment({
  network,
  store,
  missingFieldHandlers: [
    ...RelayDefaultMissingFieldHandlers,
    missingHandlerByRefConcreteTypeField,
  ],
});