JS控制输入字符长度

     <script language="javascript" type="text/javascript">
    function checkLength(ctl)
    {
       var maxLength=200;
       var nowLength=ctl.value.length;        
       if (nowLength>maxLength)
       {
            ctl.value=ctl.value.substring(0,maxLength);                      
       }
    }
    </script>

调用时：onkeyup="checkLength(this);"