how to display confirm dialog box before deleting a row in gridview by java script/vb script

<asp:ImageButton ID="btnDelete" runat="server" CausesValidation="False" CommandName="Delete" ImageUrl="~/Image/delete.png" OnClick="btnDelete_Click" Text="Delete"
OnClientClick="return confirm('Are you sure you want to Delete this record ?')" />

<asp:templatefield showheader="False" xmlns:asp="#unknown">
     <itemtemplate>
          <asp:linkbutton id="lnkBtn" commandname="Delete" text="Delete" onclientclick="return ConfirmDelete();">
runat="server">Delete</asp:linkbutton>
     </itemtemplate>
</asp:templatefield>

function ConfirmDelete()
{
    var Delet_Confirm= confirm("Do you really want to delete this record ?");
 if (Delet_Confirm== true)
 {
   return true;
 }
 else
 {
  return false;
  }
}

  protected void GridView_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        // loop all data rows
        foreach (DataControlFieldCell cell in e.Row.Cells)
        {
           // check all cells in one row
           foreach (Control control in cell.Controls)
           {
                // Must use LinkButton here instead of ImageButton
                // if you are having Links (not images) as the command button.
                ImageButton button = control as ImageButton;
                if (button != null && button.CommandName == "Delete")
                    // Add delete confirmation
                    button.OnClientClick = "if (!confirm('Are you sure " + 
                           "you want to delete this record?')) return;";
            }
        }
    }
}