请问如何在javascript里判断表单的单选框是否选中?在线等？急！

<html><head>
</head><body>
<script>
function check()
{
   if(form1.mail[0].checked){alert(form1.mail[0].value)}
   else if(form1.mail[1].checked){alert(form1.mail[1].value)}
}
</script>
<form name="form1" onsubmit="check()">
<input type="radio" name="mail" value="1" selected>aaa;
<input type="radio" name="mail" value="0">bbb
<input type="submit">
</form></body></html>