moduledStore.js

const userModule = {
  namespaced: true,
  state: () => ({}),
  mutations: {},
  actions: {},
  getters: {}
}

const organisationModule = {
  namespaced: true,
  state: () => ({}),
  mutations: {},
  actions: {},
}

const store = new VueX.Store({
  modules: {
    user: userModule,
    organisation: organisationModule
  }
})

store.state.user // -> `userModule`'s state
store.state.organisation // -> `organisationModule`'s state