Date Validation in JavaScript

var txtFromDate = document.getElementById('<%= txtDueFromDate.ClientID %>');

                var txtToDate = document.getElementById('<%= txtDueToDate.ClientID %>');

                if (txtFromDate.value.trim() == '') {

                    divDueDateSearch.innerHTML = '*Enter From Date!';

                    divDueDateSearch.style.display = 'block';

                    txtFromDate.focus();

                    return false;

                }

                if (txtFromDate.value.trim() != '' && txtFromDate.value.trim() != '__/__/__') {

                    if (!isDate(txtFromDate.value.trim())) {

                        divDueDateSearch.innerHTML = '*Enter Valid Date!';

                        divDueDateSearch.style.display = 'block';

                        txtFromDate.focus();

                        return false;

                    }

                }

                if (txtToDate.value.trim() == '') {

                    divDueDateSearch.innerHTML = '*Enter To Date!';

                    divDueDateSearch.style.display = 'block';

                    txtToDate.focus();

                    return false;

                }

                if (txtToDate.value.trim() != '' && txtToDate.value.trim() != '__/__/__') {

                    if (!isDate(txtToDate.value.trim())) {

                        divDueDateSearch.innerHTML = '*Enter Valid Date!';

                        divDueDateSearch.style.display = 'block';

                        txtToDate.focus();

                        return false;

                    }

                }

                var Date1 = new Date(txtFromDate.value.trim());

                var Date2 = new Date(txtToDate.value.trim());

                if (Date2 < Date1) {

                    divDueDateSearch.innerHTML = '*To Date should be greater than From Date!';

                    divDueDateSearch.style.display = 'block';

                    txtToDate.focus();

                    return false;

                }

                else if (Date2 >= Date1) {

                     return true;

                }

<asp:Panel ID="pnlCustomDate" runat="server" Enabled="false">

                                                                                                                    <span>From Date: </span>

                                                                                                                    <asp:TextBox ID="txtFromDate" runat="server" Width="120px"></asp:TextBox>

                                                                                                                    <asp:ImageButton runat="Server" ID="imgFromDate" ImageUrl="~/images/Calendar.gif"

                                                                                                                        ImageAlign="AbsMiddle" AlternateText="cal" />

                                                                                                                    <ajaxToolkit:CalendarExtender ID="ceSearch" runat="server" TargetControlID="txtFromDate"

                                                                                                                        CssClass="MyCalendar" Format="MM/dd/yy" PopupPosition="TopLeft" PopupButtonID="imgFromDate" />

                                                                                                                    <ajaxToolkit:MaskedEditExtender ID="meeSearch" runat="server" Mask="99/99/99" CultureName="en-US"

                                                                                                                        MaskType="Date" TargetControlID="txtFromDate" PromptCharacter="_">

                                                                                                                    </ajaxToolkit:MaskedEditExtender>

                                                                                                                    <span>To Date: </span>

                                                                                                                    <asp:TextBox ID="txtToDate" runat="server" Width="120px"></asp:TextBox>

                                                                                                                    <asp:ImageButton runat="Server" ID="imgToDate" ImageUrl="~/images/Calendar.gif" ImageAlign="AbsMiddle"

                                                                                                                        AlternateText="cal" />

                                                                                                                    <ajaxToolkit:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txtToDate"

                                                                                                                        CssClass="MyCalendar" Format="MM/dd/yy" PopupPosition="TopLeft" PopupButtonID="imgToDate" />

                                                                                                                    <ajaxToolkit:MaskedEditExtender ID="MaskedEditExtender1" runat="server" Mask="99/99/99"

                                                                                                                        CultureName="en-US" MaskType="Date" TargetControlID="txtToDate" PromptCharacter="_">

                                                                                                                    </ajaxToolkit:MaskedEditExtender>

                                                                                                                </asp:Panel>