var secondsRemaining = 60    
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { (Timer) in
        if secondsRemaining > 0 {
            print ("\(self.secondsRemaining) seconds")
            secondsRemaining -= 1
        } else {
            Timer.invalidate()
        }
    }

function animationInterval(ms, signal, callback) {
  // Prefer currentTime, as it'll better sync animtions queued in the
  // same frame, but if it isn't supported, performance.now() is fine.
  const start = document.timeline
  ? document.timeline.currentTime
  : performance.now();

  function frame(time) {
    if (signal.aborted) return;
    callback(time);
    scheduleFrame(time);
  }

  function scheduleFrame(time) {
    const elapsed = time - start;
    const roundedElapsed = Math.round(elapsed / ms) * ms;
    const targetNext = start + roundedElapsed + ms;
    const delay = targetNext - performance.now();
    setTimeout(() => requestAnimationFrame(frame), delay);
  }

  scheduleFrame(start);
}