how to use typescript, next-redux-wrapper, getServerSideProps?

I want JavaScript -> TypeScript! but, so hard.

// store.js

import { applyMiddleware, createStore, compose, Store } from "redux";
import createSagaMiddleware, { Task } from "redux-saga";
import { createWrapper } from "next-redux-wrapper";
import { composeWithDevTools } from "redux-devtools-extension";

import reducer from "./reducers";
import rootSaga from "./sagas";

const configureStore = () => {
  const sagaMiddleware = createSagaMiddleware();
  const middlewares = [sagaMiddleware];
  const enhancer =
    process.env.NODE_ENV === "production"
      ? compose(applyMiddleware(...middlewares))
      : composeWithDevTools(applyMiddleware(...middlewares));
  const store = createStore(reducer, enhancer);
  store.sagaTask = sagaMiddleware.run(rootSaga);
  return store;
};

const wrapper = createWrapper(configureStore, {
  debug: process.env.NODE_ENV === "development",
});

export default wrapper;

// reducers/index.ts

import { HYDRATE } from "next-redux-wrapper";
import { AnyAction, combineReducers } from "redux";

import url, { IUrlReducerState } from "./reducer_url";
import user, { IUserReducerState } from "./reducer_user";

export type State = {
  url: IUrlReducerState;
  user: IUserReducerState;
};

const rootReducer = (state: State, action: AnyAction) => {
  switch (action.type) {
    case HYDRATE:
      return action.payload;

    default: {
      const combineReducer = combineReducers({
        url,
        user,
      });
      return combineReducer(state, action);
    }
  }
};
export type RootState = ReturnType<typeof rootReducer>;
export default rootReducer;

reducers/index.ts <- Is this how you do it? I've changed it a little bit.

// pages/index.js

import { END } from "redux-saga";
import wrapper from "../store";

export const getServerSideProps = wrapper.getServerSideProps(
  async (context) => {

    context.store.dispatch({
      type: LOAD_USER_REQUEST,
    });

    context.store.dispatch(END);
    await context.store.sagaTask.toPromise();
  }
);

I saw the official documentation, but I don't understand: https://github.com/kirill-konshin/next-redux-wrapper#getserversideprops

These codes are not problematic in JavaScript. But there's a problem with TypeScript.

Here are the issues that I see:

1. You will get an error in createStore(reducer, enhancer) because your reducer does not fit the type (state: State | undefined, action: AnyAction) => State. You must make your reducer fit this type. The problem right now is that your reducer does not allow for state to be undefined.

change

const rootReducer = (state: State, action: AnyAction) => {

to

const rootReducer = (state: State | undefined, action: AnyAction): State => {

2. You will get an error on the line store.sagaTask = sagaMiddleware.run(rootSaga); because the store object created by redux does not have a property called sagaTask. There is another discussion about that here.

Here is one solution, based on the next-redux-wrapper docs:

define a new interface for your store which includes the task

export interface SagaStore extends Store<State, AnyAction> {
  sagaTask: Task;
}

replace

store.sagaTask = sagaMiddleware.run(rootSaga);

with

(store as SagaStore).sagaTask = sagaMiddleware.run(rootSaga);

replace

await context.store.sagaTask.toPromise();

with

await (context.store as SagaStore).sagaTask.toPromise();