在 typescript-redux 中使用 thunk 的动作创建者，将动作视为未定义

Question

为了解决这个错误，我已经工作了大约 4 个小时：

export const fetchUsers: ActionCreator<ThunkAction<
  Promise<FetchUserActions>, //type of last action
  User[], // The type for the data within the last action
  null, //extra argument
  FetchUserActions
>> = () => {
  return async (dispatch: Dispatch<AppActions>) => {
    try {
      // ususally action creators returns an obj. but this is an api request and thunk will take over, make the request and then dispatch the res.data
      const res: AxiosResponse<User[]> = await axios.get<User[]>("/users");
      if (res && res.data) {
        return dispatch({ type: ActionTypes.fetchUsers, payload: res.data });
      }
    } catch (error) {
      console.log(error);
    }
  };
};

我收到了这些错误：

 Type 'Promise<{ type: ActionTypes.fetchUsers; payload: User[]; } | undefined>' is not assignable to type 'Promise<FetchUserActions>'.
 
Type '{ type: ActionTypes.fetchUsers; payload: User[]; } | undefined' is not assignable to type 'FetchUserActions'.

Type 'undefined' is not assignable to type 'FetchUserActions'.ts(2322)

打字稿很简单，但我很难理解解释。我不明白这个 undefined 来自哪里。

export interface FetchUserActions extends Action {
  type: ActionTypes.fetchUsers;
  payload: User[];
}

Answer 1

undefined 是因为当您的 axios 响应中有错误时，您 catch 没有任何错误并且不返回任何内容（即 undefined）。