How is the correct way to work with Vuex and typescript?

Vuex is perfectly compatible with typescript using these vuex imports:

import {GetterTree, MutationTree, ActionTree} from "vuex"

The example below shows the easiest and most complete way to use vuex in typescript.

Principal store file:

import Vue from 'vue'
import Vuex from 'vuex'
import { GetterTree, MutationTree, ActionTree } from "vuex"
import MySubModule from '@/store/submodule'

Vue.use(Vuex)

class State {
    userId: string | null = null;
}

const getters = <GetterTree<State, any>>{
};

const mutations = <MutationTree<State>>{
    setUserId(state, payload) {
        state.userId = payload;
    }
};

const actions = <ActionTree<State, any>>{
    fetchUserId(store) {
    }
};

export default new Vuex.Store({
    state: new State(),
    mutations: mutations,
    actions: actions,
    modules: {
        subModuleName: MySubModule,
        //other submodules
    }
})

SubModule store file:

import { GetterTree, MutationTree, ActionTree } from "vuex"

class State {
}

const mutations = <MutationTree<State>>{
};

const actions = <ActionTree<State, any>>{
};

const MySubModule = {
    namespaced: true,
    state: new State(),
    mutations: mutations,
    actions: actions
};

export default MySubModule;

Hoping to help you !