Javascriptは、実際の文字列の残りの文字数ヒントを実現します.

//         (    ）

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 = '(    :' + 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 id="spOwner_Name"

                            style="color: #808080"><em>（50   ）</em></span>