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

import {
  Environment,
  Network,
  RecordSource,
  Store,
  QueryResponseCache,

  // Types
  CacheConfig,
  ObservableFromValue,
  GraphQLResponse,
  RequestParameters,
  FetchFunction,
  Variables,
} from 'relay-runtime';

import csrf from './lib/utils/csrf';

// 100 cache entries, 300 seconds until cache is invalid.
export const cache = new QueryResponseCache({size: 100, ttl: 300000});

export const fetchQuery: FetchFunction = (
  operation: RequestParameters,
  variables: Variables,
  cacheConfig: CacheConfig
): ObservableFromValue<GraphQLResponse> => {
  const queryId: string = operation.name;
  const cachedData: GraphQLResponse = cache.get(queryId, variables);
  const forceLoad: boolean = cacheConfig && cacheConfig.force;

  if (!forceLoad && cachedData) {
    // Return promise to keep returns consistent
    return new Promise(resolve => resolve(cachedData));
  }

  return fetch('/api/graphql', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      ...csrf.headers,
    },
    body: JSON.stringify({
      query: operation.text,
      variables,
    }),
  }).then(response => {
    const json = response.json();
    json.then(obj => cache.set(queryId, variables, obj));

    return json;
  });
};

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

export default environment;