is user logged in, in plugin

<?php
/* Handle event */
if ($modx->event->name === 'OnWebPagePrerender') {
  $jscode = "<script type='text/javascript'>
  var _gaq = _gaq || [];
  _gaq.push(['_setAccount', '".$scriptProperties['code']."']);
  _gaq.push(['_trackPageview']);

  (function() {
    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
  })();
</script>
</html>" ;
 $output = &$modx->resource->_output;
  $modx->resource->_output= str_replace("</html>",$jscode,$output);
}

$isLoggedIn = $modx->user->hasSessionContext($modx->context->get('key'));

$isLoggedIn = $modx->user->hasSessionContext('web');