ASP.NET DATAGRID 内のtextboxをJAVASCRIPTで参照したい

    Private Sub DataGrid1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataGridItemEventArgs) Handles DataGrid1.ItemDataBound

        If e.Item.ItemType = ListItemType.EditItem Then

            Dim btn_c As ImageButton = CCNT.GetControl(e.Item.Cells(3), GetType(ImageButton))
            Dim txt_c As TextBox = CCNT.GetControl(e.Item.Cells(3), GetType(TextBox))

            If btn_c Is Nothing Or txt_c Is Nothing Then
            Else
                Session("intdate") = txt_c.Text
                Dim strs As String = txt_c
                Dim strscript As String = CCNT.pop_calender_gde(strs) ーーーーー（１）

                btn_c.Attributes.Add("onclick", strscript)
            End If
        End If
    End Sub

Public Class PopCalGgrid　　−−−−−−−−−−−−−−（２）
    Inherits System.Web.UI.Page

　　　　　　　　　略
    Private Sub Btn_ok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btn_ok.Click
        Dim strscript As String
        Dim strs As String = Request.Params("source")
        Dim dtmdate As Date = Calendar1.SelectedDate
        Dim typ As String

        strscript &= "<script Language=javascript>"
        '''strscript &= "window.opener.document.Form1." & strs
        strscript &= "window.opener.document.Form1.datagrid1.[3].['" & strs　−−−ＸＸＸＸ
        strscript &= "'].value = '" & dtmdate.ToString("d") & "';"
        strscript &= "window.close();"
        strscript &= "</script>"
        Response.Write(strscript)
    End Sub
　　　　　　　略
End Class

Public Class CCONT
    Inherits core
    Public Function pop_calender_gde(ByVal strs As String) As String　−−−−−−−−（１）
        Dim strscript As String
        strscript &= "window.open('../../共用/PopCalGgrid.aspx?source=" & strs & "'"　　　　−−−−−−−（２）
        strscript &= ",'','Height=300,Width=290,Top=200,Left=300,dependent=yes,"
        strscript &= "Location=no,menubar=no,resizable=no,scroLLbar=no');"
        Return strscript
    End Function
End Class