我想弄一个把下拉选单&datepicker 调用选中的选项讯息

其实我已经弄了一个用Date() 取得时间来取得图片的代码

http://huitc.ga/hw.html

但只能在当天有效 (学校以year + month + day + classNo来命名当天功课表的相片
    

<script>
        function ImageErr(source) {
            source.src = null;
            source.onerror = "";
            source.setAttribute("style", "display: none;");
            document.getElementById("result").innerHTML = "image did not found";
            return true;
        }
        var dat = new Date();
        var year = dat.getFullYear();
        year = "" + year;
        var month = dat.getMonth() + 1;
        var day = dat.getDate();
        if(day <= 9)
            day = "0" + day;
        else
            day = "" + day;
        if(month <= 9)
            month = "0" + month;
        else
            month = "" + month;
        var className = "4B";
        var requestStr = year + month + day + className + ".jpg";
        var url = "http://www.wcbss.edu.hk/learn_teach/homework/" + requestStr;
        
        //错误照片范例，会触发 ImageErr 方法
        //var url = "http://www.wcbss.edu.hk/learn_teach/homework/201509084B.jpg";
        var text = document.getElementById("text");
        var image = document.getElementById("image");
        image.setAttribute("src", url);
        </script>

我想把以下选项被选中时和datepicker选中的日期调用至能够显示图片

例如下拉选单选了4b, datepicker选了2017.02.04
那么就会显示网址为 "http://www.wcbss.edu.hk/learn_teach/homework/" + year + month + day + className + ".jpg" 的图片
即显示 xxx.com + datepicker选项(年月日) + 下拉选单(class)选中项 + ".jpg" 的图片

<select id="class">
        　<option value="bob">4a</option>
        　<option value="nok">4b</option>
        　<option value="na">5a</option>
        　<option value="wcb">5b</option>
</select>

会的huitc716@qq.com详谈 感激不尽~!