Redux Toolkit typescript error when inyecting extra argument in Thunk Middleware

Question

I'm trying to customize the Redux Toolkit`s included Middleware to add an extra argument. This extra argument is an implementation of a Repository.

When I configure the store I add that extra argument:

export const store = configureStore({
 reducer: {
  students: students,
 },
 middleware: (getDefaultMiddleware) =>
  getDefaultMiddleware({
   thunk: {
    extraArgument: createAPIStudentRepository,
  },
  serializableCheck: false,
 }),
});

createAPIStudentRepository is of type StudentRepository:

export const createAPIStudentRepository = (): StudentRepository => {
 return {
   loadStudents: async (query: string, page: number, limit: number) => {
     const response = await fetch(API_STUDENTS_URL(query, page, limit));
     const results = (await response.json()) as Student[];
     return results;
  },
 };
};

And here is the Student repository:

export interface StudentRepository {
 loadAStudents(
   query: string,
   page: number,
   limit: number
 ): Promise<Student[]>;
}

Then, in my Redux Thunk I want to use the createAPIStudentRepository that I injected when configuring the store:

interface StudentParams {
  query?: string;
  page?: number;
  limit?: number;
}

export const fetchStudents = createAsyncThunk(
  'student/fetch',
  async (
    params: StudentParams,
    { fulfillWithValue, rejectWithValue, extra }
  ) => {
    const { query = '', page = 1, limit = 10 } = params;

   try {
     //TODO: here is the problem, extra() throws an error: "extra" is of type 
     //"unknown"
     const studentRepository = extra();
     const results = await studentRepository.loadAStudents(
       query,
       page,
       limit
     );

     return { results, page, query };
   } catch (error: unknown) {
     console.log(error);
     return rejectWithValue("Error: couldn't fetch Students");
   }
 }
);

The issue is in the TODO line. This code works but I get a Typescript error: "extra" is of type "unknwon".

Any ideas of how I can let Typescript know the type?

Reference:

• https://redux-toolkit.js.org/api/getDefaultMiddleware

Answer 1

You can explicitly type the createAsyncThunk function. See Usage with Typescript: createAsyncThunk for details.

interface StudentParams {
  query?: string;
  page?: number;
  limit?: number;
}

export const fetchStudents = createAsyncThunk<
  // Return type
  { results: Student[], page: number, query: string },
  // Argument
  StudentParams,
  // ThunkApi
  {
    extra: () => StudentRepository
  }
>(
  'student/fetch',
  async (
    params: StudentParams,
    { fulfillWithValue, rejectWithValue, extra }
  ) => {
    const { query = '', page = 1, limit = 10 } = params;

    try {
      const studentRepository = extra();
      const results = await studentRepository.loadAStudents(
        query,
        page,
        limit
      );

      return { results, page, query };
    } catch (error: unknown) {
      console.log(error);
      return rejectWithValue("Error: couldn't fetch Students");
    }
  }
);

Or you can cast the extra type. I believe the following should work.

interface StudentParams {
  query?: string;
  page?: number;
  limit?: number;
}

export const fetchStudents = createAsyncThunk(
  'student/fetch',
  async (
    params: StudentParams,
    { fulfillWithValue, rejectWithValue, extra }
  ) => {
    const { query = '', page = 1, limit = 10 } = params;

    try {
      const studentRepository = (extra as () => StudentRepository)();
      const results = await studentRepository.loadAStudents(
        query,
        page,
        limit
      );

      return { results, page, query };
    } catch (error: unknown) {
      console.log(error);
      return rejectWithValue("Error: couldn't fetch Students");
    }
  }
);