table固定表头滚动

<div class="tabflow" id="flowtable-cont">
     <table>
          <thead><tr><th>年度</th><th>起降架次(万架)</th><th>旅客吞吐(万人)</th><th>货邮吞吐(万吨)</th></tr></thead>
          <tbody>
                 <tr><td>2011</td><td>512</td><td>600</td><td>376</td></tr>
                 <tr><td>2012</td><td>504</td><td>593</td><td>397</td></tr>
                 <tr><td>2013</td><td>562</td><td>562</td><td>381</td></tr>
                 <tr><td>2014</td><td>705</td><td>464</td><td>302</td></tr>
                 <tr><td>2015</td><td>784</td><td>443</td><td>374</td></tr>
                 <tr><td>2016</td><td>645</td><td>504</td><td>415</td></tr>
                 <tr><td>2017</td><td>534</td><td>534</td><td>432</td></tr>
                 <tr><td>2018</td><td>375</td><td>582</td><td>460</td></tr>
                 <tr><td>2019</td><td>397</td><td>621</td><td>442</td></tr>
           </tbody>
      </table>
</div>

.tabflow{width: 100%;height: 17vh;overflow: auto;display: none;}
.tabflow table{font-size: 0.14rem;color: #5a5a5a; width: 100%;}
.tabflow table tr{text-align: center;line-height: 0.25rem;border: 1px solid #f2f2f2;border-right: none;}
.tabflow table thead{background-color: #fff;}
.tabflow table tbody tr:nth-child(2n+1){background-color: #f2f2f2;}
.tabflow table tbody tr td{font-size: 0.125rem;}

window.onload = function(){
     var tableflow = document.querySelector(‘#flowtable-cont‘);   //获取table元素
　　 function scrollHandle (e){
           console.log(this)
           var scrollTop = this.scrollTop;
           this.querySelector(‘thead‘).style.transform = ‘translateY(‘ + scrollTop + ‘px)‘;
     }
     tableflow.addEventListener(‘scroll‘,scrollHandle);   //监听scroll事件
}