pass a variable value from code behind to javascript

I have a hidden variable in my .aspx page.

  input type="hidden" runat="server" id="isdup" 

Now in code behind i check for certain conditions and assign isdup a value accordingly. However, this may not help you much but this is what i do in code behind.

            bool exist = (from n in mCDC.NCDCPoints
                          where n.EVENT_TYPE_ID == eventID
                          wher开发者_开发百科e n.BeginDate == begin
                          where n.EndDate == end
                          select n).Count() > 0;

    try
    {
        if (!exist)
        {
            //do this before insert so the insert will have correct values
            isdup.Value = "false";
            SaveAllColumnFields(ref ncdc, e);
            mCDC.NCDCPoints.InsertOnSubmit(ncdc);
            mCDC.SubmitChanges();
            //do this after insert because it wont work until the ncdc object
            //has been assigned an ID
            SaveAllDynamicFields(mCDC, ref ncdc, e);
            mCDC.SubmitChanges();
            Grid1.CurrentPageIndex = 0;
        }
        else
        {
            isdup.Value = "true";
            System.Windows.Forms.MessageBox.Show(isdup.Value);
        }

Now I need to access the isdup inside javascript. However the problem has been that those values are not passed and isdup is null.

    var showus= document.getElementById("<%=isdup.ClientID %>").value;
    alert(showus);
    if(showus == "true")
    {
      Showduplicate();
    }

So, kindly let me know the mistake i have been doing?

Hve you tried with:

  var showus= document.getElementById('<%=isdup.ClientID %>').value;

update

is javascript at the end of the page?

update

try to put this code in the page:

 <asp:HiddenField ID="isdup" runat="server"  Value="eee"/>
    <script>
        var showus = document.getElementById("<%=isdup.ClientID %>").value;
        alert(showus);
</script>

this works for me!

update

in page_load...

   protected void Page_Load(object sender, EventArgs e)
    {

if (!ClientScript.IsStartupScriptRegistered("clientscript"))
{
   string script1 = "<script language=JavaScript>";
   script1 += "var showus= document.getElementById('" + isdup.ClientID + "').value;";
   script1 += "alert(showus);";
   script1 += "</script>";

   ClientScript.RegisterStartupScript(typeof(Page), "clientscript", script1);
}

my example:

 protected void pagesTree_NodeClick(object sender, RadTreeNodeEventArgs e)
   {
        PageStructure page = pageService.GetPage(Guid.Parse(e.Node.Value));

        this.LoadPageData(page);

        isdup.Value = "xxx";
    }

update

         bool exist = (from n in mCDC.NCDCPoints
                      where n.EVENT_TYPE_ID == eventID
                      where n.BeginDate == begin
                      where n.EndDate == end
                      select n).Count() > 0;

 if (!ClientScript.IsStartupScriptRegistered("clientscript"))
{
   string script1 = "<script language=JavaScript>";
   script1 += "var showus= document.getElementById('" + isdup.ClientID + "').value;";
   script1 += "alert(showus);";
   script1 += "</script>";

   ClientScript.RegisterStartupScript(typeof(Page), "clientscript", script1);
}


try
{
    if (!exist)
    {
        //do this before insert so the insert will have correct values
        isdup.Value = "false";
        SaveAllColumnFields(ref ncdc, e);
        mCDC.NCDCPoints.InsertOnSubmit(ncdc);
        mCDC.SubmitChanges();
        //do this after insert because it wont work until the ncdc object
        //has been assigned an ID
        SaveAllDynamicFields(mCDC, ref ncdc, e);
        mCDC.SubmitChanges();
        Grid1.CurrentPageIndex = 0;
    }
    else
    {
        isdup.Value = "true";
        System.Windows.Forms.MessageBox.Show(isdup.Value);
    }

Try this JQuery code.

var showus= $("#<%=isdup.ClientID %>").val();

Replace your input field and try this with jquery code
UPDATED

<asp:HiddenField ID="isdup" runat="server" EnableViewState="true" />
<script type="text/javascript" src="http://code.jquery.com/jquery-1.6.1.min.js"/>
<script type="text/javascript" language="javascript">
    $(document).ready(function() {
    var showus = $("#<%=isdup.ClientID %>").val();
    alert(showus);
    if (showus == "true") {
        Showduplicate();
     }
    });
</script>