Vue3中使用reactive时,后端有返回数据但dom没有更新的解决

<template>
    <div class="aside">
        <div class="collpase-btn" @click="collpaseMenu">
            <el-icon><fold /></el-icon>
        </div>
        <el-menu
            active-text-color="#ffd04b"
            background-color="#545c64"
            class="el-menu-vertical-demo"
            default-active="2"
            text-color="#fff"
            :collapse="store.state.isCollapse"
            @open="handleOpen"
            @close="handleClose"
        >
            <el-sub-menu :index="item.id" v-for="item in menus" :key="item.id">
                <template #title>
                    <el-icon><grid /></el-icon>
                    <span>{{item.title}}</span>
                </template>
                <el-menu-item :index="it.id" v-for="it in item.subMenuList">{{it.title}}</el-menu-item>
            </el-sub-menu>
 
        </el-menu>
    </div>
</template>
<script lang="ts">
import axios from 'axios';
import { defineComponent, onMounted, reactive } from 'vue'
import { useStore } from 'vuex';
 
export default defineComponent({
    name:'Aside',
    setup() {
        const store = useStore();
        const mensList:any = [];
        let menus = reactive(mensList);
        
        const handleOpen = (key: string, keyPath: string[]) => {
 
        }
        const handleClose = (key: string, keyPath: string[]) => {
            
        };
        const collpaseMenu = () => {
            store.dispatch('collpaseChange');
        };
        onMounted(() => {
            axios.get('/user/menu').then(res => {
            menus.mensList = res.data.menusList;
        });
        });
        return {
            handleOpen,
            handleClose,
            collpaseMenu,
            store,
            menus
        }
    },
})
</script>
 
<style lang="scss" scoped>
.el-menu-item.is-active{
    background-color: var(--el-menu-hover-bg-color);;
}
.collpase-btn{
   text-align: center;
    width: 100%;
    padding: 10px 0px;
    cursor: pointer;
    .el-icon{
        color: white;
        font-size: 24px;
    }
}
</style>

const addForm = reactive({ // 这里面的reactive啥意思
  sysPre: null,
  diaPre: null,
  tem: null
})