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'
                },
​
            ]
        }
    ]
}