SOURCE

//仓库
const store = new Vuex.Store({
  state: {
    count: 1
  }
});
//foo组件
const foo = {
  template: `
						<div>
							count: {{ count }}
							countAlias: {{ countAlias }}
							countPlusLocalCount: {{ countPlusLocalCount }}
						<div>
						`,
  data() {
    return {
      localCount: 2
    };
  },
  computed: Vuex.mapState({
    //只处理仓库中的count
  	count: state => state.count*2,
    //映射
    countAlias: 'count',
    //需要用到Vue实例的话不能使用箭头函数不然this无法获取到Vue实例
    countPlusLocalCount(state) {
      return state.count + this.localCount;
    }
  })
};
//App组件
const App = {
  template: `
						<div>
							<foo></foo>
						<div>
						`,
  components: {
    foo
  }
};
//挂载App
new Vue({
  el: '#app',
  store,
  render: h => h(App)
});

<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<script src="https://unpkg.com/vuex"></script>
<div id="app"></div>