Server side data fetching using 'redux-saga'

container.js

import { fork } from 'redux-saga';
import fetchEntitySaga from './fetchEntitySaga';

export default prefetch(
  ({ getState }) => {
    if (needsFetching(getState())) {
      return fork(fetchEntitySaga, getState, ...args);
    }
  }
)(Component);

fetchEntitySaga.js

import { call, put } from 'redux-saga';
import { fetchStart, fetchSuccess, fetchFailure } from './actions/entity';

export default function *fetchEntitySaga(getState, ...args) {
  yield put(fetchStart());
  
  try {
    const result = yield call(fetch, ...args); 
    yield put(fetchSuccess(result));
  } catch (err) {
    yield put(fetchFailure(err));
  }
}

serverMiddleware.js

import createReduxSagaMiddleware from 'redux-saga';
import serverSaga from './serverSaga';

export default async function serverMiddleware(ctx, next) {
  // ...
  const reduxSagaMiddleware = createReduxSagaMiddleware();

  const store = configureStore(state, [reduxSagaMiddleware]);
  
  const locals = { getState: store.getState };
  
  // same way as react-fetcher / redial, but fetcher functions return 'fork' effects instead of promises.
  const forks = collectSagaForks( 
    routerProps.components,
    locals
  );

  if (forks.length > 0) {
    try {
      await reduxSagaMiddleware.run(serverSaga, forks).done;
    } catch (err) {
      // handle error...
    }
  }
  // ...
}

serverSaga.js

import { join } from 'redux-saga';

export default function *serverSaga(getState, forks: Array<ForkEffect>) {
  const tasks = yield forks;

  yield tasks.map(join);
};