jQuery(window).unload(function(){
  jQuery.cookie('enter', null);
});

var date = new Date();
function track_user() {
    setInterval(function() {
        date.setTime(date.getTime()+(2*1000));
        document.cookie = "enter=1; expires="+ date.toGMTString() + "; path=/";
    }, 1000);
}
track_user();

window.onbeforeunload = function(){jQuery.cookie('enter', null);}