Javascript实现真实字符串剩余字数提示

//文本框剩余字数提示(字符大小）
function textLimitCheckSj(thisArea, maxLength, SpanId) {
    var str = thisArea.value;
    if (getChrLen(str, maxLength) > maxLength * 2) {
        thisArea.value = str.substring(0, x-1);
    }
    else {
        var varss = '(剩余字数:' + Math.floor((maxLength * 2 - getChrLen(str, maxLength)) / 2) + ')';
        document.getElementById(SpanId).innerHTML = varss;
    }
}
function getChrLen(str, maxLength) {
    var realLength = 0, len = str.length, charCode = -1;
    x = 0;
    for (; (x < len) && (realLength <=maxLength * 2); x++) {
        charCode = str.charCodeAt(x);
        if (charCode >= 0 && charCode <= 128)
            realLength += 1;
        else
            realLength += 2;
    }
    return realLength;
}

<asp:TextBox ID="txtOwner_Name" runat="server" Width="200px" BackColor="LightYellow"
                        onkeyup="textLimitCheckSj(this,50,'spOwner_Name')"></asp:TextBox><span 
                            style="color: #808080"><em>（50字以内）</em></span>