load-data-epic.js

function loadDataEpic(action$) {
  return action$
    .ofType('LOAD_DATA')
    .switchMap(({ url }) =>
      fetch(url)
        .then(response => response.ok ? response.json() : requestFailedAction())
        .then(result => result.type === 'REQUEST_FAILED' ? result : requestSuccessAction(result))
        .catch(() => requestFailedAction())
    )
}