pokemon.trade/app/javascript/packs/frontend/graphqlEnvironment.ts

import {Environment, Network, RecordSource, Store} from 'relay-runtime';

function fetchQuery(operation, variables): Promise<void> {
  return fetch('/api/graphql', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      query: operation.text,
      variables,
    }),
  }).then((response): Promise<void> => response.json());
}

const environment = new Environment({
  network: Network.create(fetchQuery),
  store: new Store(new RecordSource()),
});

export default environment;