vue js select下拉框

<template>
    <ul id="select">
        <li>
            <div class="select-head">
                <span class="select-head-cont">{{cont}}</span>
                <span class="select-icon">▼</span>
            </div>
            <ul class="option">
                <li class="option-item" v-for="v in 10" @click="optionClick(v-1)">{{v-1}}</li>
            </ul>
        </li>
    </ul>
</template>
<style type="text/css">

    ul,li{
        list-style: none;
        padding: 0;
        margin: 0;
    }
    /*下拉框样式*/
    #select{
        margin-right: .05rem;
        background: rgba(0,0,0,0);
        width: .5rem;
        height: .28rem;
        font-family: "微软雅黑";
        font-size: 16px;
        color: white;
        border: 1px #DDDDDD solid;
        border-radius: 3px;
    }
    .select-head{
        overflow: hidden;
        width: 100%;
        height: .28rem;
        box-sizing: border-box;
        padding: 0 5px;
        line-height: .28rem;
    }
    .select-head .select-head-cont{
        float: left;
        color: black;
    }
    .select-head .select-icon{
        float: right;
        color: #B2B2B2;
    }
    .option{
        text-indent: 10px;
        margin-top: 1px;
        width: 100%;
        color: black;
        background: rgba(236,111,111,0.1);
        line-height: .28rem;
        border: 1px #cfcfcf solid;
        visibility: hidden;
    }
    .option-item:hover{
        background: rgba(204,106,67,0.3);
    }
</style>
<script>
    export default {
        data () {
            return {
                cont:'-',
            }
        },
        methods: {
            optionClick(v){
                this.cont='*'
                this.$emit('input', v)
                document.getElementsByClassName('option')[0].style.visibility = 'hidden';
            }
        },
        mounted(){
            let selectHead = document.getElementsByClassName('select-head')[0];
            let Option = document.getElementsByClassName('option')[0];
            let optionItem = document.getElementsByClassName('option-item');
            let itemH=optionItem[0].offsetHeight
            let Y =document.body.clientHeight-selectHead.getBoundingClientRect().bottom;

            if(Y<itemH*10){
                Option.style.webkitTransform="translate(0px,-"+(itemH*11+5)+"px)"
            }
            // console.log(Y,itemH*11,Option.offsetHeight)
            /*点击后出现下拉框*/
            selectHead.addEventListener('click',()=>{
                Option.style.visibility = 'visible';
            },false);

            /*点击其他地方时，select会收起来*/
            document.body.addEventListener('click',()=>{
                Option.style.visibility = 'hidden';
            },true);
        },
    }
</script>

效果：