配置vue-router报错、路由页面不显示问题

第一种：在index中创建好router实例，直接在main.js中引入

..................................main.js..................................

import Vue from 'vue'
import App from './App.vue'
import Router from 'vue-router'
import router from './router/index.js'
Vue.config.productionTip = false

new Vue({
	router,//错误3：此处引入的实例名必须为router，否则会报错
  render: h => h(App),
}).$mount('#app')

.................................. index.js .................................... 

import Vue from 'vue' 
import Router from 'vue-router' 
import HelloWorld from '../components/HelloWorld.vue' 
Vue.use(Router) 
const router = new Router({ 
　　mode:"history", 
　　routes:[ 
{ path:'/', redirect:HelloWorld }, 
{ path:'/HelloWorld', name:'HelloWorld', component:HelloWorld } ] 
}) 
export default router //错误1：export default {router}，页面不显示（export default用法出错：https://blog.csdn.net/hsany330/article/details/81001603）

第二种：将routes单独引入，在main.js中创建router实例
main.js
..................................

import Vue from 'vue'
import App from './App.vue'
import Router from 'vue-router'
import routes from './router/index.js'
Vue.config.productionTip = false

Vue.use(Router)
const router = new Router({
	mode:"history",
	routes:routes
})

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

　　

.................................... index.js .................................... 

import Vue from 'vue' 
import Router from 'vue-router' 
import HelloWorld from '../components/HelloWorld.vue' 
const routes = [ 
{ path:'/', redirect:HelloWorld }, 
{ path:'/HelloWorld', name:'HelloWorld', component:HelloWorld } 
] 
export default routes 

　........................APP.vue........................................

<template> 
<div id="app"> 
<img alt="Vue logo" src="./assets/logo.png"> 
<router-link to="/HelloWorld">你好</router-link> 
<router-view ></router-view> //错误2：不写<router-view>，页面不显示
 </div> 
</template> 
<script> 
export default { 
name: 'app', 
components: {},
 created() { 
    console.log(this.$route); 
    console.log(this.$router); 
    } 
 } 
</script>