Hiding an email address using javascript

I've used the code below and it works fine using onsubmit in the form tag.

<script language="JavaScript">
<!--//
function insertmail()
{
var f = document.phpformmail;
var one = "person";
var two = "@";
var three = "xyz.com";
f.recipient.value = one + two + three;
return true;
}
//-->
</script>

How can I use this, or something with a similar methodology, to hide and place an email address into this hidden input?

<input name="recipient_bcc" type="hidden" value="email@xyz.com">