How I read a js cookie the ONLY one for the site, set via below code ?

<script language="JavaScript" type="text/JavaScript">
<!--
var affiliate = <?= $affiliate ?> // value
var date = new Date();
date.setTime(date.getTime()+(90*24*60*60*1000));
var expires = "; expires="+date.toGMTString();
document.cookie = aff+"="+affiliate+expires+"; path=/";
-->
</script>