怎么计算文本域里输入了多少个字节,请教高手

<HTML>
<HEAD>
<TITLE> 字的显示 </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<SCRIPT LANGUAGE="JavaScript">
<!--
function getNo()
{
theForm.flag.value=theForm.textarea.value.length;
}
//-->
</SCRIPT>
</HEAD><BODY>
<FORM METHOD=POST ACTION="" name="theForm">
<TEXTAREA NAME="textarea" ROWS="90" COLS="260" onclick="getNo()" onmouseover="getNo()"></TEXTAREA>
<INPUT TYPE="text" NAME="flag" value="0">
</FORM>
</BODY>
</HTML>