materio-d8/web/themes/custom/materiotheme/vuejs/store/index.js

import Vue from 'vue'
import Vuex from 'vuex'
import User from './modules/user'

// https://github.com/vuejs/vuex/tree/dev/examples/shopping-cart

Vue.use(Vuex)
export default new Vuex.Store({
  modules: {
    User
  }
})