<script type="text/discourse-plugin" version="0.8">
var u = api.getCurrentUser();
if (u !== null) {
u.findDetails().then(function(u) {
if (!u.groups.some((g) => g.name === 'patrons')) {
// user isn't a patron, insert code here
}
});
}
</script>
This will work, but will be an extra request on every page load.