function orderDateOnchange(obj) {
            var Now = new Date();
            try {
                var start = $('#StartDate');
                var end = $('#EndDate');
                if (new Date(start.val()) > new Date(end.val())) {
                    alert('<asp:Literal runat="server" Text="<%$ Resources:jsMsgDateError %>" />'); //問卷查詢區間，不可大於起始日期
                            obj.val(!confirmDateTime(obj, false));
                        }

                    } catch (e) {
                        obj.value = Now.getFullYear() + "/" + PadLeft(Now.getMonth() + 1, '0', 2) + "/" + PadLeft(Now.getDate(), '0', 2) + " " + PadLeft(Now.getHours(), '0', 2) + ":" + PadLeft(Now.getMinutes(), '0', 2);
                    }
                }

 <input style="width: 120px" id="StartDate" runat="server" name="StartDate" type="text" onchange="orderDateOnchange(this)" onblur="checkdate()" />