<html>

<head>
    <meta http-equiv='content-type' content='text/html;charset=utf-8'>
    <title>WebBike V1.0</title>
    <link href="style.css" rel="stylesheet" media="screen">
</head>

<body>
    <button type='button' onclick="window.opener.document.forms['lolo'].elements['lala'].value='laurent';">Fils</button>
</body>

</html>