动态显示文本框输入的字符数

html:

 <INPUT name=lbl_limit style="font-size:12px;color:Blue;BORDER-TOP-STYLE: none; BORDER-RIGHT-STYLE: none; BORDER-LEFT-STYLE: none; BACKGROUND-COLOR: #ffffff; BORDER-BOTTOM-STYLE: none" size="48" >

JS:

   function checkMemoSize(){ 
             document.form1.lbl_limit.value="最多支持500汉字；已输入字数：" + document.getElementById("txtMemo").value.length;
             if (document.getElementById("txtMemo").value.length>500){
              document.getElementById("txtMemo").value.length=document.getElementById("txtMemo").value.substring(0,500);
                }
             }

调用：

<script language="javascript">
setInterval("checkMemoSize()", 100);
</script>