/*************************************************************************
* CodeBy:SCY CodeDate:2011年3月11日 12:01:16 
* DESC：主要是用来判断当前输入的字节数，以便做到限制输入标题的长度功能
**************************************************************************/
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>