微信小程序多层嵌套循环，三级数组遍历

<!-- 菜单标签 -->
<view class='menu_label'>
    <view class='label_ul'>
        <view wx:for="{{ menuList }}" wx:key='' class="{{ label_index == index ? 'label_lis' : 'label_li' }}" bindtap='menuList' id="{{ index }}">{{ item.title }}</view>
    </view>
</view>

<!-- 图书内容 -->
<view class='book_sec'>
    <view class='book_ul' wx:for="{{ bookUl }}" wx:key='' wx:for-item="secUl"  wx:if="{{ label_index == index }}" id="{{ index }}">
        <view class='book_li' wx:for='{{ secUl.bookSec }}' wx:key='' wx:for-item="secLi">
            <view class='book_ol'>
                <view class='book_ol_li' wx:for='{{ secLi.bookList }}' wx:key='' wx:for-item="item">
                    <view class='book_free b'>免费阅读</view>
                    <image src='{{ item.img }}'></image>
                    <view class='book_people b'>100006人在读</view>
                </view>
            </view>
        </view>
    </view>
</view>

Page({
        /**
         * 页面的初始数据
         */
        data: {
            menuList: [
                { title: '全部' },
                { title: '文学' },
                { title: '技术类' },
                { title: '社会科学' },
                { title: '设计' },
                { title: '技术类' },
                { title: '社会科学' },
            ],
            label_index: 0,
            bookUl: [
                {
                    bookSec: [
                        {
                            bookList: [
                                { img: '../../img/img1_icon.png' },
                                { img: '../../img/img2_icon.png' },
                                { img: '../../img/img3_icon.png' },
                            ]
                        },
                        {
                            bookList: [
                                { img: '../../img/img4_icon.png' },
                                { img: '../../img/img5_icon.png' },
                            ]
                        }
                    ]
                },
                {
                    bookSec: [
                        {
                            bookList: [
                                { img: '../../img/img6_icon.png' },
                                { img: '../../img/img5_icon.png' },
                                { img: '../../img/img4_icon.png' }
                            ]
                        },
                        {
                            bookList: [
                                { img: '../../img/img7_icon.png' }
                            ]
                        }
                    ]
                },
                {
                    bookSec: [
                        {
                            bookList: [
                                { img: '../../img/img7_icon.png' },
                                { img: '../../img/img2_icon.png' },
                                { img: '../../img/img1_icon.png' },
                            ]
                        },
                        {
                            bookList: [
                                { img: '../../img/img3_icon.png' },
                                { img: '../../img/img4_icon.png' },
                                { img: '../../img/img6_icon.png' }
                            ]
                        }
                    ]
                },
            ]
            
            /**
             * 菜单点击切换内容
             */
        
            menuList: function (e) {
                let that = this;
                // console.log(e);
                var id = e.target.id;
                
                that.setData({
                    label_index: id
                })
            } 
        },
    })