html

<textarea   placeholder="内容框"  id="kw"></textarea>
  
  
  
<a id="ll">清除符号</a>

js

 document.getElementById('ll').onclick = function () {   var input = document.getElementById("kw");  
 var value = input.value; 
var newValue = value.replace(/[^\u4E00-\u9FA5a-zA-Z0-9]/g, ''); 
input.value = newValue; };