Track a Google Plus "+1" in Javascript

gistfile1.html

<!-- Call google plus library-->
<script src="https://apis.google.com/js/plusone.js"></script>

<!-- Insert +1 button with callback attribute -->
<div id="plusBox">
    <g:plusone size="Tall" count="true" callback="track_googleplus">
    </g:plusone>
</div>

<!-- Add Javascript Callback function -->
<script type="text/javascript">
function track_googleplus(data){
  if(data.state=="on"){
    alert('ok');
  }
}
</script>