jquery - Javascript setInterval doesn't work correctly when tab is not active

Question

function initTimer(timeLeft) {
     var Me = this,
     TotalSeconds = 35,
     Seconds = Math.floor(timeLeft);

     var x = window.setInterval(function() {
         var timer = Seconds;

         if(timer === -1) { clearInterval(x); return; }

            $('#div').html('00:' + (timer < 10 ? '0' + timer : timer));
            Seconds--;

         },1000);
     }

I have this code. Everything works fine, when this tab is active in browser, but when I change tab and return in tab later it has problems. To be more precise, it Incorrectly displays the time.

I'd also tried setTimeout, but problem was the same.

One idea, which I have is: HTML5 Web Workers...

But here is another problem... browsers support.

can someone help to solve this problem? How can I write setInterval, which works properly,even when tab is not active

Answer 1

Use the Date object to calculate time. Don't rely on a timer firing when you ask it to (they are NOT real-time) because your only guarantee is that it'll not fire before you ask it to. It could fire much later, especially for an inactive tab. Try something like this:

function  initTimer(periodInSeconds) {
            var end = Date.now() + periodInSeconds * 1000;


            var x = window.setInterval(function() {
                var timeLeft = Math.floor((end - Date.now()) / 1000);

                if(timeLeft < 0) { clearInterval(x); return; }

                $('#div').html('00:' + (timeLeft < 10 ? '0' + timeLeft : timeLeft));
            },200);
        }

initTimer(10);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="div"></div>