一、思路说明：

这里是以城市列表数据作为索引，通过对于城市拼音的首字母进行Index索引标识，通过右侧的字母索引列表，能够快速到定位到左侧的城市列表信息，找到指定的字母Index下的所有城市列表信息数据，并且进行显示，实现了VantUI中IndexBar索引导航栏功能。

二、代码实现：

<template>
    <div class="city_body">
        <div class="city_list">
            <div class="city_hot">
                <h2>热门城市</h2>
                <ul class="clearfix">
                    <li v-for="item in hotList" :key="item.id">{{ item.nm }}</li>
                </ul>
            </div>
            <div class="city_sort" ref="city_sort">
                <div v-for="item in cityList" :key="item.index">
                    <h2>{{ item.index }}</h2>
                    <ul>
                        <li v-for="itemList in item.list" :key="itemList.id">{{ itemList.nm }}</li>
                    </ul>
                </div>
            </div>
        </div>
        <div class="city_index">
            <ul>
                <li v-for="(item, index) in cityList" :key="item.index"  @touchstart="handleToIndex(index)">{{ item.index }}</li>
            </ul>
        </div>
    </div>
</template>
    
<script>

export default {
    name: 'City',
    data() {
        return {
            cityList: [],
            hotList: []
        }
    },
    mounted() {
        this.axios.get('/api/cityList').then((res) => {
            // console.log(res);
            // 数据格式： [ { index: 'A', list: [{ nm: '北京', id: 1}]}]
            var msg = res.data.msg;
            if( msg === 'ok') {
                var cities = res.data.data.cities;
                var {cityList, hotList} =  this.formatCityList(cities);
                this.cityList = cityList;
                this.hotList = hotList;
            }
        });
    },
    methods: {
        formatCityList(cities) {
            var cityList = [];
            var hotList = [];
				
			// 热门城市列表信息		
            for(var i=0;i<cities.length; i++) {
                if(cities[i].isHot === 1){
                    hotList.push( cities[i]);
                }
            }
            
            // 城市列表信息
            for(var i=0; i<cities.length; i++) {
                var firstLetter = cities[i].py.substring(0,1).toUpperCase();
                if(toCom(firstLetter)) {  // 新添加到索引中
                    cityList.push({index: firstLetter, list: [{ nm: cities[i].nm, id: cities[i].id}]});
                }else { // 累计到已有的索引
                    for(var j=0; j<cityList.length; j++){
                        if(cityList[j].index === firstLetter) {
                            cityList[j].list.push(  { nm: cities[i].nm, id: cities[i].id} );
                        }
                    }
                }
            }

            // 城市数据索引index的排序
            cityList.sort((n1,n2) => {
                if(n1.index > n2.index) {
                    return 1;
                }
                else if (n1.index < n2.index) {
                    return -1;
                } else {
                    return 0;
                }
            })

            // 判断index是否存在于cityList中
            function toCom(firstLetter) {
                for(var i=0;i<cityList.length;i++){
                    if(cityList[i].index === firstLetter) {
                        return false;
                    }
                }
                return true;
            }

            // console.log(cityList);
            // console.log(hotList);
            return {
                cityList,
                hotList
            }
        },
        // 点击右侧索引，左侧城市列表也滚动到指定的位置
        handleToIndex(index) {
            var h2 = this.$refs.city_sort.getElementsByTagName('h2');
            this.$refs.city_sort.parentNode.scrollTop = h2[index].offsetTop;
        }
    }
}
</script>

//  style样式代码
<style scoped>
#content .city_body{ margin-top: 45px; display: flex; width:100%; position: absolute; top: 0; bottom: 0;}
.city_body .city_list{ flex:1; overflow: auto; background: #FFF5F0;}
.city_body .city_list::-webkit-scrollbar{
    background-color:transparent;
    width:0;
}
.city_body .city_hot{ margin-top: 20px;}
.city_body .city_hot h2{ padding-left: 15px; line-height: 30px; font-size: 14px; background:#F0F0F0; font-weight: normal;}
.city_body .city_hot ul li{ float: left; background: #fff; width: 29%; height: 33px; margin-top: 15px; margin-left: 3%; padding: 0 4px; border: 1px solid #e6e6e6; border-radius: 3px; line-height: 33px; text-align: center; box-sizing: border-box;}
.city_body .city_sort div{ margin-top: 20px;}
.city_body .city_sort h2{ padding-left: 15px; line-height: 30px; font-size: 14px; background:#F0F0F0; font-weight: normal;}
.city_body .city_sort ul{ padding-left: 10px; margin-top: 10px;}
.city_body .city_sort ul li{ line-height: 30px; line-height: 30px;}
.city_body .city_index{ width:20px; display: flex; flex-direction:column; justify-content:center; text-align: center; border-left:1px #e6e6e6 solid;}
</style>