var startTime = new Date();           //Start the clock!
setInterval('recordTime(true)', 1000);

window.onbeforeunload = function() {  //When the user leaves the page(closes the window/tab, clicks a link)...
   recordTime();
}
function recordTime() {
   var endTime = new Date();          //Get the current time.
   var timeSpent = (endTime - startTime);        //Find out how long it's been.
   var xmlhttp;        //Make a variable for a new ajax request.
   if (window.XMLHttpRequest) {       //If it's a decent browser...
       // code for IE7+, Firefox, Chrome, Opera, Safari
       xmlhttp = new XMLHttpRequest();        //Open a new ajax request.
   } else {       //If it's a bad browser...code for IE6, IE5
       xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");        //Open a different type of ajax call.
   }
   //console.info(timeSpent);
   var url = "Server/TimeTrackSubmission.jsp?time="+timeSpent;    //Send the time on the page to a php script of your choosing.
   xmlhttp.open("GET",url,false);        //The false at the end tells ajax to use a synchronous call which wont be severed by the user leaving.
   xmlhttp.send(null);        //Send the request and don't wait for a response.
}