I am trying to use the following code to get a reference to a modalpopupextender, but when I check the value of the javascript variable 'modal' it is always null. What is the proper way to get a reference to the AJAX control using javascript?

.vb

        Dim myStringBuilder As New StringBuilder(246)
        myStringBuilder.AppendFormat("      <script type=""text/javascript"">{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("            var modal = $find('<%=modal1.ClientID%>');{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("            debugger;{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("            $find('<%=modal1.ClientID%>').add_showing({0}", Environment.NewLine)
        myStringBuilder.AppendFormat("                function(){0}", Environment.NewLine)
        myStringBuilder.AppendFormat("                {{{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("                    alert(""Modal popup will be showing"");{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("                }}{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("            );{0}", Environment.NewLine)
        myStringBuilder.AppendFormat("      </script>{0}", Environment.NewLine)
        ClientScript.RegisterStartupScript(Me.GetType(), "myJSalert", myStringBuilder.ToString())

.aspx

        <ajaxToolkit:ModalPopupExtender ID="mpeResetConfirm" runat="server"
        TargetControlID="btnReset" PopupControlID="pnlConfirmation" BehaviorID="modal1"/>

Problem solved here

I removed the code behind and added this to the .aspx page

    <script type="text/javascript" language="javascript">
        function pageLoad() 
        {
            var modal = $find('modal1');
            debugger;
            $find('modal1').add_showing(
                function()
                {
                    alert("Modal popup will be showing");
                }
           );  
        }
    </script>

swolff1978, thanks for posting this information.  I had been having a hard time referencing a modalpopupextender from my javascript code (and may possibly still be).  Currently, I'm having an issue with referencing the show() method of my modalpopupextender.  Here is a quick rundown:

Overview:  I have a custom control that contains a wizard control.  On that wizard control I am attempting to transfer the validationsummary information into a modalpopupextender rather than displaying a validationsummary on the page itself.  I have a modalpopupextender sitting inside my wizard control which I am referencing from javascript on the aspx.  I have added some attributes to three controls that pass the control into my javascript function.  Details follow...

Error:  Object doens't support this property or method.

Codebehind (this codes sits in the Page_PreRender method):

((Button)this.FindControl("wizDCS$StepNavigationTemplateContainerID$StepNextButton")).Attributes.Add("onclick", "mVsInit('ValSumDiv', " + wizDCS.WizardSteps[6].FindControl("mpeValSum_Info") + ", 'no');");
((Button)this.FindControl("wizDCS$StepNavigationTemplateContainerID$StepNextButton")).Attributes.Add("onmouseup", "mVsInit('ValSumDiv', '" + wizDCS.WizardSteps[6].FindControl("mpeValSum_Info") + "', 'no');");
this.Attributes.Add("onload", "mVsInit('ValSumDiv', '" + wizDCS.WizardSteps[6].FindControl("mpeValSum_Info") + "', 'no');");

Javascript:

    var objVSMH = new oVsModalHandler();
    
    ...
    
    function mVsInit(val4, val5, val6)
    {
        objVSMH.setInternalDiv(val4);
        objVSMH.setVsCtrl(val5);
        objVSMH.setInit(val6);
        objVSMH.GetStarted();
    }
    
    function oVsModalHandler()
    {
        var internalDiv = "";
        var internalVsCtrl = null;
        var internalInit = "";
        
        function mValSumModalDialog()
        {
            var mpe = internalVsCtrl;
            Page_ClientValidate();
            if (!Page_IsValid)
                mpe.show();
        }
        
        this.setInternalDiv = function(val4)
        {
            internalDiv = val4;
        }
        
        this.setVsCtrl = function(val5)
        {
            internalVsCtrl = val5;
        }
        
        this.setInit = function(val6)
        {
            internalInit = val6;
        }
        
        this.GetStarted = function()
        {
            mValSumModalDialog();
        }
    }

Ok, I figured it out.  Perhaps it isn't the best way to handle it, but it is working just fine so I thought I'd post it here.  Initially, I had the modalpopupextender and associated controls stored within one of the steps on the wizard.  Here are the steps I took:

1. Since I was having a hard time referencing the control from javascript because it was embedded in the wizard step, I opted to move that stuff out of the steptemplate and after the wizard control.
   
2. I got rid of all my previous validationsummary handlers and created a single validationsummary control to handle all the summary listings
3. I added the following javascript functions:
   

   function ShowModalDialog(mpeId)
   {
       Page_ClientValidate();
       if (!Page_IsValid)
           $find('mpeBVS0').show();
    }
   
    function init()
    {
       $get('VSDiv0').style.display = 'none';
    }

   
   
4. Then I added the handlers on the "next" button in the wizard to check for errors before going on (all in the Page_PreRender:
   

   ((Button)this.FindControl("wizDCS$StepNavigationTemplateContainerID$StepNextButton")).Attributes.Add("onclick", "ShowModalDialog('" + mpeVS0.ClientID + "');");        ((Button)this.FindControl("wizDCS$StepNavigationTemplateContainerID$StepNextButton")).Attributes.Add("onmouseup", "ShowModalDialog('" + mpeVS0.ClientID + "');");
   this.Attributes.Add("onload", "init();");

   
   

Now, instead of having multiple validationsummary controls, I have one control handling all my errors while still having the modalpopup behavior.