vue 动态绑定NavMenu 导航菜单（两级）

<el-menu
          :default-active="$route.path"
          unique-opened
          router
          :collapse="isCollapse"
          :collapse-transition="false"
        >
          <el-submenu
            :index="item.root_id + ''"
            v-for="item in menuList"
            :key="item.root_id"
          >
            <template slot="title">
              <i :class="iconObj[item.root_id]"></i>
              <span>{{ item.root_name }}</span>
            </template>
            <el-menu-item
              :index="'/' + subItem.root_url"
              v-for="subItem in item.children"
              :key="subItem.root_id"
            >
              <i class="el-icon-menu"></i>{{ subItem.root_name }}
            </el-menu-item>
          </el-submenu>
        </el-menu>