passing value from child from to parrent in javascript

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ASP.NET

i have one parent form and a child form.
i am passing the value of selected id from radgrid to child page.and receive the value through query string
like this..................

var text;
   function RowSelected(sender, args) {
       document.getElementById("<%=Label4.ClientID %>").innerHTML = args.getDataKeyValue("Number");
       text = document.getElementById("<%=Label4.ClientID %>").innerHTML;

   }

   function ClosedClicked() {

       window.open("PurchaseOrderpopuptest.aspx?controlID=" + text);
   }

in my child page receiving value like this
.....................................

string controlID = "";
       protected void Page_Load(object sender, EventArgs e)
       {
         controlID = Request["controlID"].ToString ();
         TextBox1.Text = controlID;
       }

...........................
then what i want to do is i want send the value back to parrent page

function sendvalue() {

            var textval = document.getElementById('TextBox1').value;
            alert(textval);          
            window.opener.document.forms.namedItem('Label6') = textval;        
            window.close();
            return false;
        } 

if i comment this line

window.opener.document.forms.namedItem('Label6') = textval;

then the script execute but with htis line script is not executing
so, anyone help me how to solve this problem.
label6 is the control of parent page
Thank You