后台管理系统中根据用户权限显示不同菜单是很基础的需求，使用vue开发通常我们是遍历路由（this.$router.options.routes)生成用户菜单，vue中提供了addRouter()方法用于动态挂载路由，我们可以根据用户权限结合该方法实现用户路由动态生成。代码如下：

（1） router.js：该文件中初始化一个VueRouter对象，并挂载一些无需权限校验即可访问的路由：

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

Vue.use(Router)

/* Layout */
import Layout from '@/layout'

/**
 * 初始化路由（无需权限）
 */
export const ConstantRoutes = [
  {
    path: '/login',
    component: () => import('@/views/login/index'),
    hidden: true
  },
  {
    path: '/404',
    component: () => import('@/views/404'),
    hidden: true
  },
  {
    path: '/',
    component: Layout,
    redirect: '/dashboard',
    children: [
      {
        path: 'dashboard',
        name: 'Dashboard',
        component: () => import('@/views/dashboard/index'),
        meta: {
          title: '系统首页',
          icon: 'dashboard'
        }
      }
    ]
  }
]

// 定义一个函数来创建router
export const createRouter = routes => new Router({
  mode: 'history',
  routes
})

const router = createRouter(ConstantRoutes)

/**
 * 路由重置，防止router未初始化导致重复挂载
 */
export function resetRouter() {
  const newRouter = createRouter()
  router.matcher = newRouter.matcher // reset router
}

export default router

（2） dynamicRoutes.js：该文件中定义需要根据用户权限动态挂载显示的路由：

import Layout from '@/layout'
/**
 * 动态路由，需要根据用户权限动态挂载
 */
const DynamicRoutes = [
  {
    path: '/system',
    component: Layout,
    redirect: '/system/user',
    name: 'System',
    meta: {
      title: '系统管理',
      icon: 'example',
      permission: 'MENU_SYSTEM'
    },
    children: [
      {
        path: 'user',
        name: 'User',
        component: () => import('@/views/system/user/index'),
        meta: {
          title: '用户管理',
          icon: 'table',
          permission: 'MENU_SYSTEM_USER'
        }
      },
      {
        path: 'role',
        name: 'Role',
        component: () => import('@/views/system/role/index'),
        meta: {
          title: '角色管理',
          icon: 'table',
          permission: 'MENU_SYSTEM_ROLE'
        }
      },
      {
        path: 'dict',
        name: 'Dict',
        component: () => import('@/views/system/dict/index'),
        meta: {
          title: '字典管理',
          icon: 'table',
          permission: 'MENU_SYSTEM_DICT'
        }
      }
    ]
  },
]

export default DynamicRoutes

（3）permission.js：该文件用于路由跳转前的权限校验，如：token校验、获取用户信息生成用户动态菜单等

import router from './router'
import DynamicRoutes from './router/dynamicRoutes'
import store from './store'
import { Message } from 'element-ui'
import NProgress from 'nprogress' // progress bar
import 'nprogress/nprogress.css' // progress bar style
import { getToken } from '@/utils/auth' // get token from cookie
import getPageTitle from '@/utils/get-page-title'
import Layout from '@/layout/index'

NProgress.configure({ showSpinner: false }) // NProgress Configuration

const whiteList = ['/login'] // no redirect whitelist

/**
 * 根据用户权限生成路由
 * @param DynamicRoutes 动态路由表
 * @param permissions 用户权限
 */
export function generateMenu(DynamicRoutes, permissions) {
  const routers = []
  DynamicRoutes.forEach((route) => {
    if (route.meta.permission == undefined || route.meta.permission == null || permissions.indexOf(route.meta.permission) > -1) {
      let child = route.children
      route.children = []
      if (child !== undefined && child.length > 0) {
        route.children = generateMenu(child, permissions)
      }
      routers.push(route)
    }
  })
  return routers;
}

router.beforeEach(async(to, from, next) => {
  
  NProgress.start()

  // 判断是否登录
  const hasToken = getToken()

  if (hasToken) {
    if (to.path === '/login') {
      next({ path: '/' })
      NProgress.done()
    } else {
      const hasGetUserInfo = store.getters.name
      if (hasGetUserInfo) {
        next()
      } else {
        try {
          // 获取用户信息
          store.dispatch('getInfo').then((data) => {
          	// data.permissions是请求后台获取到的权限列表
            const routers = generateMenu(DynamicRoutes, data.permissions)
            let constantRouters = router.options.routes
            constantRouters = constantRouters.concat(routers)
            // 注意：'/404'必须挂载在路由的最后位置
            constantRouters.push({
              path: '*', redirect: '/404', hidden: true
            })
            // addRouter是让挂载的路由生效，但是挂载后'router.options.routes'并未刷新(八成是个bug)，所以还需要手动将路由加入'router.options.routes'
            router.addRoutes(routers)
            router.options.routes = constantRouters
            next()
          })
        } catch (error) {
          // remove token and go to login page to re-login
          await store.dispatch('user/resetToken')
          Message.error(error || 'Has Error')
          next(`/login?redirect=${to.path}`)
          NProgress.done()
        }
      }
    }
  } else {
    /* has no token*/

    if (whiteList.indexOf(to.path) !== -1) {
      // in the free login whitelist, go directly
      next()
    } else {
      // other pages that do not have permission to access are redirected to the login page.
      next(`/login?redirect=${to.path}`)
      NProgress.done()
    }
  }
})

router.afterEach(() => {
  // finish progress bar
  NProgress.done()
})

易错点总结：
（1）动态挂载路由时addRouter不会导致’router.options.routes’的刷新，需要我们手动将生成的路由列表设置到router.options.routes中；
（2）/404路由必须放在路由表的最后。