解决Element ui导航栏选中背景色刷新消失的问题

<el-menu
        :is-collapse="isCollapse"
        text-color="#fff"
        active-text-color="#fff"
        :default-active="activerouter"
        :router="true"
      >
</el-menu>
 //重点在于:default-active="activerouter"的设置

data() {
    return:activerouter;
}

mounted() {
    this.activerouter =  window.location.pathname
   //正常情况下加上这句话是可以解决的，如果解决不了，继续往下看
  },

<el-menu-item
            :index="subItem.path"
            class="active_bg"
            :class="{ active_bg: index == activeIndex }"
            @click="selectMenuItem(subItem.path)"
          >
</el-menu-item>

selectMenuItem(path) {
      this.activerouter = path
      window.sessionStorage.setItem("activerouter", path);
    },

mounted() {
    //获取地址栏中的路由，设置elementui中的导航栏选中状态
    this.activerouter =  window.sessionStorage.getItem("activerouter");
    console.log('activerouter',this.activerouter)
  },

<!--侧边菜单-->
         <el-menu :default-active="active" class="el-menu-vertical-demo" router>
            <router-link to="/user" style="text-decoration: none">
              <el-menu-item index="/user" v-if="isflag" @click="selectMenuItem('/user')"> 
                <el-icon><User /></el-icon>
                <span>User Information</span>
              </el-menu-item>
            </router-link>
            <el-menu-item index="order" v-if="isflag" @click="selectMenuItem('order')">
              <el-icon><Tickets /></el-icon>
              <span>Order Management</span>
            </el-menu-item>
            <el-menu-item index="manage" v-if="userInfo.rolename=='op' ? false : true" @click="selectMenuItem('manage')">
              <el-icon><Reading /></el-icon>
              <span>Task Management</span>
            </el-menu-item>
            <el-menu-item index="task" v-if="isflag" @click="selectMenuItem('task')">
              <el-icon><Calendar /></el-icon>
              <span>Schedule</span>
            </el-menu-item>
          </el-menu>

  data() {
    return {
      active: "/user",
    };
  },

mounted(){
    this.active =  window.sessionStorage.getItem("activerouter");
  },

  methods: {
    selectMenuItem(path) {
      this.active = path
      window.sessionStorage.setItem("activerouter", path);
    },
   }