See https://github.com/erikras/ducks-modular-redux (but here we add epics as well)

reducers.js

export const UPDATE_EDITOR_CONTENT = 'mock_test/UPDATE_EDITOR_CONTENT';
export const updateMockTestContent = (testId: number, content: string) => ({
  type: UPDATE_EDITOR_CONTENT,
  testId,
  content,
});
handlers[UPDATE_EDITOR_CONTENT] = (state, action) => {
  const { testId, content } = action;
  return state
    .setIn(['tests', 'items', testId, 'answer'], content)
    .setIn(['tests', 'items', testId, 'lastUpdated'], Date.now());
};
const updateEditorContentEpic = action$ => action$
  .ofType(UPDATE_EDITOR_CONTENT)
  .debounceTime(500)
  .mergeMap(({ testId, content }) => (
    EJApi.updateMockTestContent(testId, { content })),
  )
  .map(responseToAction(SUCCESS_UPDATE_EDITOR_CONTENT));

export const SUCCESS_UPDATE_EDITOR_CONTENT = 'mock_test/SUCCESS_UPDATE_EDITOR_CONTENT';
handlers[SUCCESS_UPDATE_EDITOR_CONTENT] = (state, action) => {
  const data = fromJS(action.data);
  const testId = data.get('id');

  // we shouldn't use the data from the server
  return state.setIn(['tests', 'items', testId, 'isFetching'], false);
};

// epics
export const mockTestEpics = [
  updateEditorContentEpic,
];

// default export
export default createReducer(initialState, handlers);