javascript取My97 DatePicker控制中的日期

jsp页面代码：

<span>付款时间：</span>
<input name="beginCreateDate" id="beginCreateDate" type="text" readonly="readonly" maxlength="20" class="laydate-icon form-control layer-date input-sm"
value="<fmt:formatDate value="${machGoodsDaySale.beginCreateDate}" pattern="yyyy-MM-dd"/>"
onclick="WdatePicker({dateFmt:'yyyy-MM-dd',maxDate:'#F{$dp.$D(\'endCreateDate\')}'});"/> - 
<input name="endCreateDate" id="endCreateDate" type="text" readonly="readonly" maxlength="20" class="laydate-icon form-control layer-date input-sm"
value="<fmt:formatDate value="${machGoodsDaySale.endCreateDate}" pattern="yyyy-MM-dd"/>"
onclick="WdatePicker({dateFmt:'yyyy-MM-dd',minDate:'#F{$dp.$D(\'beginCreateDate\')}'});"/>

只能用 这种

var beginCreateDate = document.getElementById("beginCreateDate").value;
var endCreateDate = document.getElementById("endCreateDate").value;

不能用 

$("#beginCreateDate").val();