JS简单限制textarea内输入字符数量的方法

<script> 
function getStringUTFLength(str) { 
 var value = str.replace(/[\u4e00-\u9fa5]/g," ");
 //将汉字替换为两个空格
 return value.length; 
} 
function leftUTFString(str,len) { 
 if(getStringUTFLength(str)<=len) { 
  return str; 
 }
 var value = str.substring(0,len); 
 while(getStringUTFLength(value)>len) { 
  value = value.substring(0,value.length-1); 
 } 
 return value; 
} 
function count() { 
 var len=255;
 var value = document.getElementById("licenseother").value; 
 if(getStringUTFLength(value)>=len) {  
  document.getElementById("licenseother").value = leftUTFString(document.getElementById("licenseother").value,len); 
 } 
 document.getElementById("result").value = len-getStringUTFLength(document.getElementById("licenseother").value); 
} 
</script> 
<table width="100%"> 
 <tr>
  <td> 
   <textarea cols=100 rows=4 id="licenseother" onkeypress="count()" onkeyup="count()" onblur="count();" onChange="count();"></textarea> 
  </td>
 </tr> 
 <tr>
  <td> 
   本输入框限制输入255个字符(汉字计算为2个字符) &nbsp;剩余字符数：
   <input readonly type="text" size="3" id="result" value="255"> 
  </td>
 </tr> 
</table>