这是vue的代码，都在里面了，为什么不显示div中的每个li呢？

<template>
  <div class="index">
    <div class="container">
      <div class="swiper-box">
        <div class="nav-menu">
          <ul class="menu-wrap">
            <li class="menu-item">
              <a href="javascript:;">手机 电话卡</a>
              <div class="children">
                <ul v-for="(item,index) in menuList" :key="index">
                  <li v-for="product in item" :key="product.id">
                    <a :href="product? '/#/product/' + product.id : ''">
                      ![](product.img ? product.img : )
                      {{product ? product.name : '小米9'}}
                    </a>
                  </li>
                </ul>
              </div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">电视 盒子</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">笔记本 平板</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">家电 插线板</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">出行 穿戴</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">智能 路由器</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">电源 配件</a>
              <div class="children"></div>
            </li>
            <li class="menu-item">
              <a href="javascript:;">生活 箱包</a>
              <div class="children"></div>
            </li>
          </ul>
        </div>
        <swiper :options="swiperOptions">
          <swiper-slide v-for="(item,index) in slideList" :key="index">
            <a :href="'/#/product/' + item.id">
              ![](item.img)
            </a>
          </swiper-slide>
          <div class="swiper-pagination"  slot="pagination"></div>
          <div class="swiper-button-prev" slot="button-prev"></div>
          <div class="swiper-button-next" slot="button-next"></div>
        </swiper>
      </div>
      <div class="ads-box"></div>
      <div class="banner"></div>
      <div class="product-box"></div>
    </div>
    <service-bar></service-bar>
  </div>
</template>

<script>
import ServiceBar from './../components/ServiceBar'
import { swiper, swiperSlide } from 'vue-awesome-swiper'
import 'swiper/dist/css/swiper.css'
export default {
  name: 'index',
  components: {
    ServiceBar,
    swiper,
    swiperSlide
  },
  data () {
    return {
      swiperOptions: {
        autoplay: {
          delay: 4000
        },
        loop: 'true',
        effect: 'cube',
        pagination: {
          el: '.swiper-pagination',
          clickable: 'true'
        },
        navigation: {
          nextEl: '.swiper-button-next',
          prevEl: '.swiper-button-prev'
        }
      },
      slideList: [
        {
          id: '42',
          img: '/imgs/slider/slide-1.jpg'
        },
        {
          id: '45',
          img: '/imgs/slider/slide-2.jpg'
        },
        {
          id: '46',
          img: '/imgs/slider/slide-3.jpg'
        },
        {
          id: '',
          img: '/imgs/slider/slide-4.jpg'
        },
        {
          id: '',
          img: '/imgs/slider/slide-5.jpg'
        }
      ],
      menuList: [
        [
          {
            id: 30,
            img: './imgs/item-box-1.png',
            name: '小米CC9'
          },
          {
            id: 31,
            img: './imgs/item-box-2.png',
            name: '小米8青春版'
          },
          {
            id: 32,
            img: './imgs/item-box-3.jpg',
            name: 'Redmi K20 Pro'
          },
          {
            id: 33,
            img: './imgs/item-box-4.jpg',
            name: '移动4G专区'
          }
        ], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]
      ]
    }
  }
}
</script>

<style lang="scss" scoped>
@import '../assets/base.scss';
@import '../assets/config.scss';
@import '../assets/mixin.scss';
.index{
  .swiper-box{
    .swiper-container{
      height: 451px;
      img{
      width: 100%;
      height: 100%;
      }
      .swiper-button-prev{
        left: 274px;
      }
      /deep/ .swiper-pagination-bullet-active {
        background: #fff;
      }
    }
    .nav-menu{
      width: 264px;
      height: 451px;
      position: absolute;
      z-index: 2;
      padding-top: 26px;
      padding-bottom: 26px;
      background-color: #55585a82;
      box-sizing: border-box;
      .menu-wrap{
        .menu-item{
          height: 50px;
          line-height: 50px;
          &:hover{
            background: $colorA;
          }
          a{
            display: block;
            position: relative;
            color: $colorG;
            font-size: $fontI;
            padding-left: 30px;
            &:after{
              position: absolute;
              top: 17.5px;
              right: 30px;
              content: '';
              @include bgImg(10px,15px,'/imgs/icon-arrow.png');
            }
          }
          .children{
            width: 962px;
            height: 451px;
            background-color: $colorG;
            position: absolute;
            left: 264px;
            top: 0;
            border: 1px solid $colorH;
            box-sizing: border-box;
            ul{
              display: flex;
              justify-content: space-between;
              height: 75px;
              li{
                height: 75px;
                line-height: 75px;
                flex: 1;
                padding-left: 23px;
              }
            }
          }
        }
      }
    }
  }
}
</style>

效果是这样的：

谢谢各位！

楼主的menuList数组有问题，console控制台肯定会报错。
楼主把menuList设置为二维数组，固定设置问题不大。（一般不会这么用，因为后台传过来的数据一般为json，你这数组就不满足json格式）。
menuList数组后面的

[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]

会导致第二层循环中product为0，从而在控制台报错“product.id未定义”

<li v-for="product in item" :key="product.id">

我不明白楼主为什么把menuList数组设置这么复杂，且不便于从后台获取。
正确的做法：
(1) 设置对象数组

menuList:
        [
          {
            id: 30,
            img: './imgs/item-box-1.png',
            name: '小米CC9'
          },
          {
            id: 31,
            img: './imgs/item-box-2.png',
            name: '小米8青春版'
          },
          {
            id: 32,
            img: './imgs/item-box-3.jpg',
            name: 'Redmi K20 Pro'
          },
          {
            id: 33,
            img: './imgs/item-box-4.jpg',
            name: '移动4G专区'
          }
        ]

（2） 设置json数组

menuList:{
    name:"手机 电话卡",
    children: [
          {
            id: 30,
            img: './imgs/item-box-1.png',
            name: '小米CC9'
          },
          {
            id: 31,
            img: './imgs/item-box-2.png',
            name: '小米8青春版'
          },
          {
            id: 32,
            img: './imgs/item-box-3.jpg',
            name: 'Redmi K20 Pro'
          },
          {
            id: 33,
            img: './imgs/item-box-4.jpg',
            name: '移动4G专区'
          }
        ]
  }

key是需要该数组有唯一的值，你这每个都是0了，key值不唯一了，下面就会有问题