how to access master page control in child page .aspx page(in javscript)

Question

hi

in my master page.cs i am assiging an value to hiddenfield hfSession="abc"; in my content page(default.aspx) i need to access this value in my javscript

   <script type="text/javascript" language="javascript">
        function(sender, e) 
    { 
var Sessioninfo= $get('<%= ((Hiddenfield)this.Master.FindControl("ct100_hfSession")).ClientID %>');
          </script>

but here i get an error :object reference not set to an instance of an object

Answer 1

you can try like...

document.getElementById('<%= txt.ClientID %>')

Answer 2

I use this little javascript util function:

// This function returns a control's (mangled) client id given its ASP.NET Id
function GetClientId(strid) {
var count = document.forms[0].length;
var i = 0;
var eleName;
for (i = 0; i < count; i++) {
    eleName = document.forms[0].elements[i].id;
    pos = eleName.indexOf(strid);
    if (pos >= 0) break;
}
return '#' + eleName;
}

Answer 3

Use,

Sessioninfo= $get('<%= ((Hiddenfield)this.Master.FindControl("hfSession")).ClientID %>');