index.ts

import { createStore } from 'vuex';

// The modules to import
import auth, { Store as AuthStore, State as AuthState } from './auth';
import counter, { Store as CounterStore, State as CounterState } from './counter';

// A State type with all the submodules
type State = {
  auth: AuthState;
  counter: CounterState;
}

// And the store is an extension of all the stores but each store receives its own state
export type Store = AuthStore<Pick<State, 'auth'>> & CounterStore<Pick<State, 'counter'>>;

const store = createStore({
  modules: {
    auth,
    counter,
  },
});

export function useStore() {
  // This made the trick to me, i dont love it, but i dont know other way to do it.
  // The compiler kept complaining about it not being compatible with Vuex' store so i casted it to uknnown
  // and after that re-casted as the Store we just defined.
  return store as unknown as Store;
}

export default store;

No worries, we are using community effort here...if this remains to be unresolved, I will open up an issue to Vuex repository and/or write to core team members in Discord channel 😁

Vue 3 and Vue Router 4 (in beta) are written fully in TypeScript, however, Vuex 4 is not. It's TypeScript rewrite is coming up in Vuex 5 later on. But they have been working towards better TS support already with this version 4, which is still in beta.

Here's an issue thread in Vuex repo related to using modules in Vuex 4.0: vuejs/vuex#1833

I just realized VS Code intellisense is not showing type information for the store instance after passing it from useStore function, when used inside component. Works if imported in .ts file.