Vuex data updated but views not updated

  javascript, question

Description: vue2 plus webpack for vuex

Vuex changed the data through mutations. the data was indeed updated, but the page was not updated. through investigation, it was found that the problem was referring to store method.
The following is code:

//index.js
 "use strict";
 import Vue from 'Vue';
 import Vuex from 'vuex';
 import store from '../../vuex/store.js';
 import VueRouter from 'vue-router';
 import routers from '../../routers/routers';
 Vue.use(Vuex);
 Vue.use(VueRouter);
 
 Vue.config.debug = true;  //Open error prompt
 
 const router = new VueRouter({
 //mode: 'history',
 //scrollBehavior: () => ({ y: 0 }),
 routes: routers
 })
 
 
 //vuex
 //const store = new Vuex.Store({
 //    state: {
 //        count: 0
 //    },
 //    mutations: {
 //increment: state = > state.countplus,
 //        decrement: state => state.count--
 //    }
 //})
 
 const app = new Vue({
 router,
 store,
 computed: {
 indexData () {
 return this.$store.state.count
 bracket
 },
 methods: {
 increment () {
 this.$store.commit('increment')
 },
 decrement () {
 this.$store.commit('decrement')
 bracket
 },
 mounted: function () {
 },
 }).$mount('#app')
//index.html
 <div id="app">
 <h1>Hello App!  </h1>
 <p>
 <div>vuex data: {{ indexData }}</div>
 <div><a href="javascript:;"  @click="increment">IncrementCount</a></div>
 <div><a href="javascript:;"  @click="decrement">DecrementCount</a></div>
 </p>
 </div>
//store.js
 import Vue from 'vue';
 import Vuex from 'vuex';
 Vue.use(Vuex);
 
 const state ={
 count: 0
 bracket
 const mutations ={
 Count plus
 decrement: state => state.count--
 bracket
 
 export default new Vuex.Store({
 state,
 mutations
 })

These are the main codes
Using import to introduce store in index.js will cause description problems.
If you directly define store in index.js, the above problem will not occur.

Vue wrote in the store. . . Stupid ratio problem