详解vuex数据传输的两种方式及this.$store undefined的解决办法

import Store from './store'

//main.js
import Vue from 'vue'
import App from './App'
import store from './store'
import router from './router'
import ElementUI from 'element-ui'
import 'element-ui/lib/theme-chalk/index.css'

Vue.config.productionTip = false
Vue.use(ElementUI)

new Vue({
 router,
 store,
 render: h => h(App)
}).$mount('#app')

//store/index.js
import Vue from "vue";
import Vuex from "vuex";

Vue.use(Vuex);

 const store = new Vuex.Store({
  state: {
    n:101
  }
})
export default store

//view部分,即真正的可视化的部分, 这个任何一个组件都可以
<template>
  <div>
    {{ n }}
  </div>
</template>
<script>
export default {
 computed: {
  n () {
    return this.$store.state.n
  }
 }
}
</script>

//main.js - 去掉了store的声明
import Vue from 'vue'
import App from './App'
import router from './router'
import ElementUI from 'element-ui'
import 'element-ui/lib/theme-chalk/index.css'

Vue.config.productionTip = false
Vue.use(ElementUI)

new Vue({
 router,
 render: h => h(App)
}).$mount('#app')

//store/index.js - 这个文件和上面的一样
//想要使用vuex数据的组件. 注意,此时$store是无效的,所以只能通过store.state.n来获取
<template>
  <div>
    {{ n }}
  </div>
</template>
<script>
import store from './store'
export default {
 computed: {
  n () {
    return store.state.n
  }
 }
}