something.js

<script type="text/javascript">
  var since = '<%= @since.to_f %>';
  var updater = setInterval( function() {
      new Ajax.Updater('notes','/poller', {
        method:'get',
        parameters:"since="+since,
        insertion:'top',
        onSuccess:function(r) { since = r.responseText; }
      })
    }, 4000);
</script>