testEpic.js

// @flow
import Rxjs from 'rxjs';

import { ajax } from 'rxjs/observable/dom/ajax';

const { Observable } = Rxjs;

const retryActionOnError = (action, error, retryCount = 0, delay = 5000) => {
  if (retryCount && action.retry && action.retry >= retryCount) {
    return Observable.of({ ...action, payload: error, error: true });
  }

  return Observable.of({ ...action, retry: (action.retry || 0) + 1 }).delay(delay);
};

export const testEpic = (action$: Object) => {
  return action$
    .filter(action => action.type === 'FETCH_EPIC')
    .do(x => console.log('EPIC ACTION ', x))
    .mergeMap(
      action =>
        (action.error
          ? Observable.of({ type: 'FETCH_ERROR', payload: action.payload })
          : ajax
            .getJSON('https://yandex.ru/123')
            .map(r => ({ type: 'UPDATE_EPIC', payload: r }))
            .catch(e => retryActionOnError(action, e, 3, 1000))
            .takeUntil(action$.ofType('FETCH_EPIC'))
            .takeUntil(action$.ofType('CANCEL_EPIC'))),
    );
};

        <Button onPress={() => this.props.dispatch({ type: 'FETCH_EPIC', payload: Date.now() })}>
          Epic
        </Button>
        <Button onPress={() => this.props.dispatch({ type: 'CANCEL_EPIC', payload: Date.now() })}>
          Cancel Epic
        </Button>