vuex：
state===>相当于 vue里面的data
mutations====>相当于vue 里面的methods方法
getter==》相当于vue 里面的computed 计算属性

import vuex from 'vuex'
Vue.use(vuex)//挂载

const store = new vuex.Store({
  state: {
    scrollTag: false,
    currency: 'HKD'
  },
  mutations: {
    getScolltagTrue(state) {
      state.scrollTag = true
    },
    getScolltagFalse(state) {
      state.scrollTag = false
    },
    updateCurrencyToChange(state, obj) {
      state.currency = obj
    }

  }
})

new Vue({
  el: '#app',
  router,
  render: h => h(App),
  store//注册
})

在组件中：

  watch: {
            moneys: {
                handler: function (val, oldVal) {
                    window.localStorage.setItem('xingChengCurrency', val)
                    this.$store.commit('updateCurrencyToChange', val)
                },
                deep: true//深度监视
            }
        },