How to Pause the timer on window blur and resume the timer on window focus event?

Thanks for seeing my question. I am using wp-pro-quiz plugin for quiz. I want to know that how can I pause the timer if the window is not in focus or is blur and resume it when it is back to focus.? My code:

 var timelimit = (function() {
        var _counter = config.timelimit;
        var _intervalId = 0;
        var instance = {};

        instance.stop = function() {
            if(_counter) {
                window.clearInterval(_intervalId);
                globalElements.timelimit.hide();
            }
        };

        instance.start = function() {
        var x;
            if(!_counter)
                return;
        var $timeText = globalElements.timelimit.find('span').text(plugin.methode.parseTime(_counter));
            var $timeDiv = globalElements.timelimit.find('.wpProQuiz_progress');

            globalElements.timelimit.show();
            $.winFocus(function(event) {
               console.log("Blur\t\t", event);
           },
           function(event) {
             console.log("Focus\t\t", event);
          x = _counter * 1000;
            });



            var beforeTime = +new  Date();

            _intervalId = window.setInterval(function() {

                var diff = (+new Date() - beforeTime);
                var elapsedTime = x - diff;

                if(diff >= 500) {
                    $timeText.text(plugin.methode.parseTime(Math.ceil(elapsedTime / 1000)));
                }

                $timeDiv.css('width', (elapsedTime / x * 100) + '%');

                if(elapsedTime <= 0) {
                    instance.stop();
                    plugin.methode.finishQuiz(true);
                }

            }, 16);
        };

        return instance;

    })();

via Chebli Mohamed