Check User Stay time in a page using javascript

<script type="text/javascript">

    var time;

    window.onload = function() {

   // Initialize "time" variable to "0".

    time = 0;

    }

    window.setInterval(calcTime, 1000);

    function calcTime() {

      // calculate user-stay time

        time += 1;

    }

    // notify a handler the user-stay time as a query string before the page is unloaded.

    window.onbeforeunload = function() {

    var oRequest = new XMLHttpRequest();

        oRequest.open("get", "/handlers/HandlerTest.ashx?"+time, false);

        oRequest.send(null);

               

    }