Can you get parameter values of reportviewer at runtime?

Question

I have a very specific question about the reporting services report viewer control.

I appreciate any help. I am a bit of a novice with Javascript on the client side, but I have to use this in my project.

THE REQUIREMENT

I need to retrieve the current value of a single parameter on a report viewer control embedded in a webpart at runtime. I need to access the value using Javascript on the client side.

Can this even be done? The reportviewer doesn't appear to get rendered.

THE HTML CODE FOR THE REPORT VIEWER

<asp:UpdatePanel ID="UpdatePanel1" runat="server" OnUnload="UpdatePanel_Unload">
    <ContentTemplate>
            <rsweb:ReportViewer ID="ReportViewer1" runat="server" 
            Font-Names="Verdana" Font-Size="8pt" Height="383px" 
            InteractiveDeviceInfos="(Collection)" ProcessingMode="Remote" 
            WaitMessageFont-Names="Verdana" WaitMessageFont-Size="14pt" Width="757px" 
            SizeToReportContent="True">
        </rsweb:ReportViewer>
    </ContentTemplate>
</asp:UpdatePanel>

Answer 1

UPDATE- WORKING CODE BELOW

The key was creating a custom data attribute as @Fil indicated in this link (http://html5doctor.com/html5-custom-data-attributes/) and passing from the code behind and then accessing the $.cache. And passing the clientID of the reportviewer into the javascript function to get to the current instance of the webpart child controls.

<input type="hidden" id="<%= ASP_SSRS.ClientID %>_myDataState" 
onchange="compareUnitValues(this.id, this.parentNode.id, '<%= ReportViewer1.ClientID %>',  '<%= ASP_SSRS.ClientID %>', '<%= btnSendHiddenField.ClientID %>');" />

<script type ="text/javascript">
function compareUnitValues(elemt, parent, reportviewerID, value1, value2) {
  var myDataUnit = $("#" + elemt),
     parentObject = $("#" + parent),
     reportviewerObject = $("#" + reportviewerID),
     ssrs    = $("#" + value1),
     btnSend = $("#" + value2);

  var myDataUnitValue = myDataUnit.val();
  var myDataUnitJSON = jQuery.parseJSON(myDataUnitValue);
  var currentmyDataUnit = myDataUnitJSON.currentUnit.objectId;
  var sessioncurrentObjectId = document.getElementById('<%= hiddenCurrentObjectId.ClientID %>').value;
  ssrs.val(myDataUnitValue);
  var currentReportViewerParam = $("#" + reportviewerID).attr("data-report-param");

  if (currentmyDataUnit != currentReportViewerParam) {
  btnSend.trigger("click");
  }    

}

FROM CODE BEHIND CREATE THE CUSTOM DATA ATTRIBUTE

ReportViewer1.Attributes.Add("data-report-param", parsedObjectId)