JS判断字串字节数，并截取长度

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>