上一篇章介绍了用户登录的过程。那么，用户登录成功后，根据权限，渲染侧边栏菜单。首先我们看一下前端的根目录的路由信息。

  {
    path: '',
    component: Layout,
    redirect: 'index',
    children: [
      {
        path: 'index',
        component: () => import('@/views/index'),
        name: 'Index',
        meta: { title: '首页', icon: 'dashboard', affix: true }
      }
    ]
  }

这里包含了两个部分，组件Layout和@view/index。主要关注下Layout组件。
看看src/Layout/index.vue：

<template>
  <div :class="classObj" class="app-wrapper" :style="{'--current-color': theme}">
    <div v-if="device==='mobile'&&sidebar.opened" class="drawer-bg" @click="handleClickOutside"/>
    <sidebar v-if="!sidebar.hide" class="sidebar-container" />
    <div :class="{hasTagsView:needTagsView,sidebarHide:sidebar.hide}" class="main-container">
      <div :class="{'fixed-header':fixedHeader}">
        <navbar />
        <tags-view v-if="needTagsView" />
      </div>
      <app-main />
      <right-panel>
        <settings />
      </right-panel>
    </div>
  </div>
</template>

这里包含了sidebar, navbar, settings等组件。sidebar对应的是左侧菜单栏。我们看下src/Layout/components/Siderbar/index.vue：

<template>
    <div :class="{'has-logo':showLogo}" :style="{ backgroundColor: settings.sideTheme === 'theme-dark' ? variables.menuBackground : variables.menuLightBackground }">
        <logo v-if="showLogo" :collapse="isCollapse" />
        <el-scrollbar :class="settings.sideTheme" wrap-class="scrollbar-wrapper">
            <el-menu
                :default-active="activeMenu"
                :collapse="isCollapse"
                :background-color="settings.sideTheme === 'theme-dark' ? variables.menuBackground : variables.menuLightBackground"
                :text-color="settings.sideTheme === 'theme-dark' ? variables.menuColor : variables.menuLightColor"
                :unique-opened="true"
                :active-text-color="settings.theme"
                :collapse-transition="false"
                mode="vertical"
            >
                <sidebar-item
                    v-for="(route, index) in sidebarRouters"
                    :key="route.path  + index"
                    :item="route"
                    :base-path="route.path"
                />
            </el-menu>
        </el-scrollbar>
    </div>
</template>

<script>
import { mapGetters, mapState } from "vuex";
import Logo from "./Logo";
import SidebarItem from "./SidebarItem";
import variables from "@/assets/styles/variables.scss";

export default {
    components: { SidebarItem, Logo },
    computed: {
        ...mapState(["settings"]),
        ...mapGetters(["sidebarRouters", "sidebar"]),
        activeMenu() {
            const route = this.$route;
            const { meta, path } = route;
            // if set path, the sidebar will highlight the path you set
            if (meta.activeMenu) {
                return meta.activeMenu;
            }
            return path;
        },
        showLogo() {
            return this.$store.state.settings.sidebarLogo;
        },
        variables() {
            return variables;
        },
        isCollapse() {
            return !this.sidebar.opened;
        }
    }
};
</script>

可以看出，是根据sidebarRouters构建出菜单项。这里的sidebar-item也是一个自定义组件，用于构建多级菜单。我们看一下sidebar-item组件：

<template>
  <div v-if="!item.hidden">
    <template v-if="hasOneShowingChild(item.children,item) && (!onlyOneChild.children||onlyOneChild.noShowingChildren)&&!item.alwaysShow">
      <app-link v-if="onlyOneChild.meta" :to="resolvePath(onlyOneChild.path, onlyOneChild.query)">
        <el-menu-item :index="resolvePath(onlyOneChild.path)" :class="{'submenu-title-noDropdown':!isNest}">
          <item :icon="onlyOneChild.meta.icon||(item.meta&&item.meta.icon)" :title="onlyOneChild.meta.title" />
        </el-menu-item>
      </app-link>
    </template>

    <el-submenu v-else ref="subMenu" :index="resolvePath(item.path)" popper-append-to-body>
      <template slot="title">
        <item v-if="item.meta" :icon="item.meta && item.meta.icon" :title="item.meta.title" />
      </template>
      <sidebar-item
        v-for="child in item.children"
        :key="child.path"
        :is-nest="true"
        :item="child"
        :base-path="resolvePath(child.path)"
        class="nest-menu"
      />
    </el-submenu>
  </div>
</template>

我们再回到src/Layout/components/Siderbar/index.vue，看下sidebarRouters是怎么获取值的。...mapGetters(["sidebarRouters", "sidebar"]),这里用到的是vuex知识，就是从store的getters中去获取，我们在store/getters中sidebarRouters: state => state.permission.sidebarRouters，接下来看下src/store/modules/permissions.js：

import auth from '@/plugins/auth'
import router, { constantRoutes, dynamicRoutes } from '@/router'
import { getRouters } from '@/api/menu'
import Layout from '@/layout/index'
import ParentView from '@/components/ParentView'
import InnerLink from '@/layout/components/InnerLink'

const permission = {
  state: {
    routes: [],
    addRoutes: [],
    defaultRoutes: [],
    topbarRouters: [],
    sidebarRouters: []
  },
  mutations: {
    SET_ROUTES: (state, routes) => {
      state.addRoutes = routes
      state.routes = constantRoutes.concat(routes)
    },
    SET_DEFAULT_ROUTES: (state, routes) => {
      state.defaultRoutes = constantRoutes.concat(routes)
    },
    SET_TOPBAR_ROUTES: (state, routes) => {
      state.topbarRouters = routes
    },
    SET_SIDEBAR_ROUTERS: (state, routes) => {
      state.sidebarRouters = routes
    },
  },
  actions: {
    // 生成路由
    GenerateRoutes({ commit }) {
      return new Promise(resolve => {
        // 向后端请求路由数据
        getRouters().then(res => {
          const sdata = JSON.parse(JSON.stringify(res.data))
          const rdata = JSON.parse(JSON.stringify(res.data))
          const sidebarRoutes = filterAsyncRouter(sdata)
          const rewriteRoutes = filterAsyncRouter(rdata, false, true)
          const asyncRoutes = filterDynamicRoutes(dynamicRoutes);
          rewriteRoutes.push({ path: '*', redirect: '/404', hidden: true })
          router.addRoutes(asyncRoutes);
          commit('SET_ROUTES', rewriteRoutes)
          commit('SET_SIDEBAR_ROUTERS', constantRoutes.concat(sidebarRoutes))
          commit('SET_DEFAULT_ROUTES', sidebarRoutes)
          commit('SET_TOPBAR_ROUTES', sidebarRoutes)
          resolve(rewriteRoutes)
        })
      })
    }
  }
}

// 遍历后台传来的路由字符串，转换为组件对象
function filterAsyncRouter(asyncRouterMap, lastRouter = false, type = false) {
  return asyncRouterMap.filter(route => {
    if (type && route.children) {
      route.children = filterChildren(route.children)
    }
    if (route.component) {
      // Layout ParentView 组件特殊处理
      if (route.component === 'Layout') {
        route.component = Layout
      } else if (route.component === 'ParentView') {
        route.component = ParentView
      } else if (route.component === 'InnerLink') {
        route.component = InnerLink
      } else {
        route.component = loadView(route.component)
      }
    }
    if (route.children != null && route.children && route.children.length) {
      route.children = filterAsyncRouter(route.children, route, type)
    } else {
      delete route['children']
      delete route['redirect']
    }
    return true
  })
}

function filterChildren(childrenMap, lastRouter = false) {
  var children = []
  childrenMap.forEach((el, index) => {
    if (el.children && el.children.length) {
      if (el.component === 'ParentView' && !lastRouter) {
        el.children.forEach(c => {
          c.path = el.path + '/' + c.path
          if (c.children && c.children.length) {
            children = children.concat(filterChildren(c.children, c))
            return
          }
          children.push(c)
        })
        return
      }
    }
    if (lastRouter) {
      el.path = lastRouter.path + '/' + el.path
    }
    children = children.concat(el)
  })
  return children
}

// 动态路由遍历，验证是否具备权限
export function filterDynamicRoutes(routes) {
  const res = []
  routes.forEach(route => {
    if (route.permissions) {
      if (auth.hasPermiOr(route.permissions)) {
        res.push(route)
      }
    } else if (route.roles) {
      if (auth.hasRoleOr(route.roles)) {
        res.push(route)
      }
    }
  })
  return res
}

export const loadView = (view) => {
  if (process.env.NODE_ENV === 'development') {
    return (resolve) => require([`@/views/${view}`], resolve)
  } else {
    // 使用 import 实现生产环境的路由懒加载
    return () => import(`@/views/${view}`)
  }
}

export default permission

可以看到，是通过getRouter函数去获取路由信息，然后通过filterAsyncRouter递归调用构造我们需要的结构，最后一起整合到路由中。getRouter的代码如下：

// 获取路由
export const getRouters = () => {
  return request({
    url: '/getRouters',
    method: 'get'
  })
}

就是向服务端发送getRouters的请求，等待返回。这里我们找到了构造菜单的函数，那是从哪里调用的呢。答案是从路由守卫。我们再回到src/permissions.vue中：

router.beforeEach((to, from, next) => {
  NProgress.start()
  if (getToken()) {
    to.meta.title && store.dispatch('settings/setTitle', to.meta.title)
    /* has token*/
    if (to.path === '/login') {
      next({ path: '/' })
      NProgress.done()
    } else {
      if (store.getters.roles.length === 0) {
        isRelogin.show = true
        // 判断当前用户是否已拉取完user_info信息
        store.dispatch('GetInfo').then(() => {
          isRelogin.show = false
          store.dispatch('GenerateRoutes').then(accessRoutes => {
            // 根据roles权限生成可访问的路由表
            router.addRoutes(accessRoutes) // 动态添加可访问路由表
            next({ ...to, replace: true }) // hack方法 确保addRoutes已完成
          })
        }).catch(err => {
            store.dispatch('LogOut').then(() => {
              Message.error(err)
              next({ path: '/' })
            })
          })
      } else {
        next()
      }
    }
  } else {
    // 没有token
    if (whiteList.indexOf(to.path) !== -1) {
      // 在免登录白名单，直接进入
      next()
    } else {
      next(`/login?redirect=${to.fullPath}`) // 否则全部重定向到登录页
      NProgress.done()
    }
  }
})

就是每次访问地址之前，先判断store中是否有存储的role信息（store.getters.roles.length === 0），如果没有就通过store.dispatch(‘GenerateRoutes’)进行获取路由信息。