史诗般的命名函数与箭头函数-Redux Observable

Question

当我将其声明为箭头函数时，我创建的史诗似乎无效。但是，当更改为命名函数时-一切正常。

有人对可能出什么问题有任何想法吗？

export const userEpic = action$ => action$.ofType(GET_USER).mergeMap(action =>
  Observable.fromPromise(methods.getUsers({ params: action.payload }))
    .map(payload => ({ type: GET_USER_SUCCESS, payload }))
    .catch(error => Observable.of({ type: GET_USER_ERROR, payload: error }))
    .takeUntil(action$.ofType(GET_USER_CANCELLED)));

vs

export function userDetailsEpic(action$) {
  return action$.ofType(GET_USER).mergeMap(action => Observable.fromPromise(methods.getUsers({ params: action.payload }))
    .map(payload => ({ type: GET_USER_SUCCESS, payload }))
    .catch(error => Observable.of({ type: GET_USER_ERROR, payload: error }))
    .takeUntil(action$.ofType(GET_USER_CANCELLED)));