I have this timer (see Code below). How can I make sure that the countdown starts AND keeps counting down only if the browser window is onFocus?
(I want it to pause if the user opens another window, for example.)
//Countdown
function timerCountdown()
{
    x=100;
    document.getElementById('timer1').value=x;
    x=x-1;
    t=setTimeout("timerCountdown()",1000);
    if (c<-1)
    {
        document.getElementById('timer1').value='Go';
        clearTimeout(t);
    }
}
 
     
    