jQuery计算textarea中文字数(剩余个数)的小程序

代码如下:
<div class="area">
        <p>
            还可以输入<b class="num">140</b>字</p>
        <textarea class="chackTextarea"></textarea>
    </div>

 
<script type="text/javascript">
    var txtobj = {
        divName: "area", //外层容器的class
        textareaName: "chackTextarea", //textarea的class
        numName: "num", //数字的class
        num: 140 //数字的最大数目
    }
    var textareaFn = function () {
        //定义变量
        var $onthis; //指向当前
        var $divname = txtobj.divName; //外层容器的class
        var $textareaName = txtobj.textareaName; //textarea的class
        var $numName = txtobj.numName; //数字的class
        var $num = txtobj.num; //数字的最大数目
        function isChinese(str) {  //判断是不是中文
            var reCh = /[u00-uff]/;
            return !reCh.test(str);
        }
        function numChange() {
            var strlen = 0; //初始定义长度为0
            var txtval = $.trim($onthis.val());
            for (var i = 0; i < txtval.length; i++) {
                if (isChinese(txtval.charAt(i)) == true) {
                    strlen = strlen + 2; //中文为2个字符
                } else {
                    strlen = strlen + 1; //英文一个字符
                }
            }
            strlen = Math.ceil(strlen / 2); //中英文相加除2取整数
            if ($num - strlen < 0) {