如何watch dom<template lang="html"> <div class="a">   <div class="goods-container">       <div class="goods-left" ref="leftScroll">         <ul>           <li class="goods-left-list" :class="{'active':currentIndex===idex}" v-for="(item,idex) in goods" :key='item.name' @click="tofood(idex)">             <span class="text border-1px">               <span class="icon" v-if="item.type>0" :class="icon[item.type]"></span>{{item.name}}             </span>           </li>         </ul>       </div>data() {     return {       goods: [],       icon: ['decrease', 'discount', 'guarantee', 'invoice', 'special'],       listHeight: [],       scorllY: 0,       foodInfo: {},       dom: this.$refs.leftScroll     };   }, ``watch: {dom(newvalue,oldvalue) {   console.log("aaa");   console.log(newvalue+"-------"+oldvalue); }}, 無論是普通dom 還是for 循環(huán)的都watch 不了 （普通的是不是因為沒有變化才沒有監(jiān)聽到）   但打印data 中的 數(shù)據(jù)dom  顯示undefinde