mounted(){
 //记录每个内容对用的dom数组
 this.arrDom = document.getElementsByClassName("item-content");
 window.addEventListener('scroll', this.handleScroll);
 },
 
 destroyed(){
 window.removeEventListener('scroll', this.handleScroll);
 },

tabList:[{
 id:1,
 name:'详情'
 },{
 id:2,
 name:'评论'
 },{
 id:3,
 name:'新闻'
 },{
 id:4,
 name:'关于'
 },{
 id:5,
 name:'相关'
 }],

<nav :class="headerFixed" id='tab'>
 <div @click='handleSelectTab(item.id)' :class="active==item.id" v-for='item in tabList' :key='item.id'>{{item.name}}</div>
</nav>
<div class="item-content">
 <div>11111111</div>
</div>
<div class="item-content">
 <div>22222</div>
</div>
<div class="item-content">
 <div>33333</div>
</div>
<div class="item-content">
 <div>44444</div>
</div>
<div class="item-content">
 <div>555555</div>
</div>

handleScroll(){
 let scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop;
 this.headerFixed = scrollTop > this.offsetTop;
 for (let i = 0; i < this.arrDom.length; i++) {
  //因为下面使用到了i+1，所以需要把最后一个分离出来判断
 if(this.arrDom[this.arrDom.length-1].offsetTop-scrollTop>80){
  if(this.arrDom[i].offsetTop-scrollTop<=80&&this.arrDom[i+1].offsetTop-scrollTop>80){
  this.active = i+1
  }
 }else{
  this.active = this.arrDom.length;
 }
 
 }
 },