layer.open输入字数实时显示

    {
                    field: ‘mainSupervision‘,
                    align: ‘center‘,
                    title: ‘监督要点‘,
                    formatter: function (value, row, index) {
                        var html = $.common.sprintf("<input onclick=openWin(‘%s‘) class=‘form-control‘ type=‘text‘ name=‘task[%s].mainSupervision‘ value=‘%s‘>", index, index, value);
                        return html;
                    }
                },

 //点击监督要点输入框时的弹窗
    function openWin(i) {
        var key = "task[" + i + "].";
        var text = $("input[name=‘"+ key + "mainSupervision" + "‘]").val();
        var num=0;
        if(text){
           num=text.length;
        }
        layer.open({
            title: "监督要点",
            type: 1,
            content: "<div class=\"col-sm-8\">\n" +
                "                    <textarea id=\"supDesc\" placeholder=\"输入1-1000个字符\"" +
                "                              onkeyup=\"texLength(this, 1000, ‘stepDescLength‘);\"\n" +
                "                              maxlength=\"1000\" class=\"form-control\" style=\"height: 280px;width: 770px\">"+text+"</textarea>\n" +
                "                <div style=\"display: inline-block;padding-left: 700px\">\n" +
                "                    <span id=\"stepDescLength\">"+num+"</span><span class=\"num_count\">/1000</span>\n" +
                "                </div>\n" +
                "            </div>", //这里content是一个DOM，注意：最好该元素要存放在body最外层，否则可能被其它的相对元素所影响
            area:["800px","400px"],
            btn: [‘确认‘],
            yes: function(index, layero){
                $("input[name=‘"+ key + "mainSupervision" + "‘]").val($("#supDesc").val());
                layer.close(index);
            }
        });
    }

/**
 * 计算还可以输入多少字
 * @param obj
 * @param maxlength
 * @param id
 */
function texLength(obj, maxlength, id) {
   var curr = obj.value.length;
   if (curr >= maxlength) {
      layer.msg(‘字数在‘ + maxlength + ‘字以内‘);
      document.getElementById(id).innerHTML = maxlength;
   } else {
      document.getElementById(id).innerHTML = curr;
   }
}