var matchwords;
        function notifytextlength() {
            var inputnum = document.getelementbyid(txttitle).value.replace(/[^\x00-\xff]/g, **).length; //得到输入的字节数
            if (inputnum <= 200) {
matchwords = document.getelementbyid("txttitle").value.length;
document.getelementbyid("inputedword").innerhtml = inputnum + "字节," + matchwords + "字符";
document.getelementbyid("inputtingword").innerhtml = (200 - inputnum) + "字母,"+(math.round(((200-inputnum)/2)-0.5))+"汉字";
}
if (inputnum > 200) {
                document.getelementbyid(txttitle).value = document.getelementbyid(txttitle).value.substring(0, matchwords);
 //如果超过200字节，就截取到200字节
             }
}
<input id="txttitle" type="text" class="inputtext" runat="server" onpropertychange="notifytextlength();" />
当前已经输入<span id="inputedword" style="color:red"></span> 还可以输入<span id="inputtingword" style="color:red;"></span>