路由守卫判断是否是登陆页面

import Vue from 'vue'
import Router from 'vue-router'

const login= () => import('./components/login.vue')
const routerB = () => import('./components/routerB.vue')
const routerC  = () => import('./components/routerC.vue')
const routerD = () => import('./components/routerD.vue')
Vue.use(Router)
const router = new Router({
  routes: [
    { path: '/', redirect: '/login' },
    { path: '/login', component: login},
    {
      path: '/routerB ',
      component: routerB ,
      redirect: '/routerB ',
      children: [
        { path: '/routerC  ', component: routerC },
        { path: '/routerD ', component: routerD }
      ]
    }
  ]
})
// 挂载路由导航守卫,to表示将要访问的路径，from表示从哪里来，next是下一个要做的操作 next('/login')强制跳转login
router.beforeEach((to, from, next) => {
  // 访问登录页，放行
  if (to.path === '/login') return next()
  // 获取token
  const token = window.sessionStorage.getItem('token')
  // 没有token, 强制跳转到登录页
  if (!token) return next('/login')
  next()
})
export default router