还能输入多少字？(JS动态计算)

        <div class="m-form ovh">
            <div class="hd">
                <span class="fr" id="message">还能输入200个字</span>
                我要说：
                <select name="select" id="select">                    
                   <option value="12">北京</option>
                   <option value="13">上海</option>
                   <option value="14">深圳</option> </select>
            </div>
            <div class="bd">
                <textarea name="textarea" id="textarea" cols="45" rows="5" onkeyup="checkLength()" maxlength="200"></textarea>
                <p class="ovh">
                    <input type="button" value="" class="btn-send fr" onclick="HandComment()"/>
                    <span class="fr" style="display:none;">发送成功</span>
                </p>
            </div>
        </div>

    /*动态计算能够输入的字数*/
    function checkLength() {
        var maxChars = 200;
        if ($("#textarea").val().length > maxChars)
            $("#textarea").val($("#textarea").val().substring(0, maxChars));
        var curr = "还能输入" + (maxChars - $("#textarea").val().length) + "个字";
        $("#message").html(curr.toString());
    }