const router = new VueRouter({
 routes: [
  {
   path: '/foo',
   component: Foo,
   beforeEnter: (to, from, next) => {
    // ...
   }
  }
 ]
})

beforeEnter(to,from,next)
// to  要进入的目标，路由对象
// from 当前导航正要离开的路由
// next 初步认为是展示页面；（是否显示跳转页面）
​
next()//直接进to 所指路由
next(false) //中断当前路由
next('route') //跳转指定路由
next('error') //跳转错误路由

import Vue from 'vue';
import VueRouter from 'vue-router';
Vue.use(VueRouter);
​
import Index from './Index/Index.vue'
​
import AA from './views/AA.vue'
import DD from './views/DD.vue'
import EE from './views/EE.vue'
export default {
  routes: [
    {
      path: '/',
      component: Index,
      name: 'index',
      children: [
        {
          path: 'AA',
          component: AA,
          name: 'aa',
          beforeEnter: (to, from, next) => {
            if (to.path == '/DD') {
              next()
            } else {
              alert('请登入');
              next('/DD')
            }
​
          }
        }, {
          path: 'DD',
          component: DD,
          name: 'dd'
        },
        {
          path: 'EE',
          component: EE,
          name: 'ee'
        },
​
      ]
    }
  ]
}