自适应输入框

<textarea class="common"  placeholder="测试测试测试" id="txt"></textarea> 
 <script type="text/javascript">  
  const txt = document.getElementById("txt");  
  txt.addEventListener('input', (e) => { 
     txt.style.height = 'auto'
     txt.style.height = txt.scrollHeight + 2 + 'px'; 
   }, false); 
 </script>
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