js计算字数

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<meta name="robots" content="all" />
<meta name="author" content="" />
<meta name="Copyright" content="" />
<meta name="keywords" content="" />
<meta name="description" content="JS限制textarea输入框输入字数" />
<title>JS统计还可以输入多少字数，用于向输入者提示信息</title>
<SCRIPT language="javascript">
<!--
function checktext(text)
{
    allValid = true;
    for (i = 0;  i < text.length;  i++)
    {
      if (text.charAt(i) != " ")
      {
        allValid = false;
        break;
      }
    }
return allValid;
}

function gbcount(message,total,used,remain)
{
  var max;
  max = total.value;
  if (message.value.length > max) {
  message.value = message.value.substring(0,max);
  used.value = max;
  remain.value = 0;
 <!-- alert("留言不能超过 200 个字!");-->
 alert("不能超过"+total.value+"个字!");
  }
  else {
  used.value = message.value.length;
  remain.value = max - used.value;
  }
}

-->
</script>
<style type="text/css">
<!--
* {padding:0; margin:0;}
body, html {text-align:left; font-size:12px; line-height:150%; margin:0 auto; background:#fff; padding-top:20px;}
fieldset {padding:10px; width:550px; margin:0 auto;}
legend {font-size:14px; font-weight:bold;}
.inputtext {border:none; background:#fff;}
-->
</style>
</head>
<body>
<form action="SaveData.asp" method="post" >
<fieldset><legend>请输入内容</legend>
<textarea name="Memo" rows="10" wrap=PHYSICAL cols="75" onKeyDown="gbcount(this.form.Memo,this.form.total,this.form.used,this.form.remain);" onKeyUp="gbcount(this.form.Memo,this.form.total,this.form.used,this.form.remain);"></textarea>
<p>最多字数：
<input disabled maxLength="4" name="total" size="3" value="10" class="inputtext">
已用字数：
<input disabled maxLength="4" name="used" size="3" value="0" class="inputtext">
剩余字数：
<input disabled maxLength="4" name="remain" size="3" value="10" class="inputtext"></td>
</p>
</fieldset>
</form>
</body>
</html>