Smooth html5 compass movement

I'm trying to smooth the compass movement of an app using the HTML5 Compass API.

I understood I need to make a low-pass filter, I found this wich seems to be perfect http://ift.tt/1DAaQjA :

onSensorChanged(angle) {
 lastSin = smoothingFactor * lastSin + (1-smoothingFactor) * sin(angle)
 lastCos = smoothingFactor * lastCos + (1-smoothingFactor) * cos(angle)
}

getAngle() {
 return atan2(lastSin, lastCos)
}

but I can't make it work using javascript.

Currently I have something like that :

var compass = document.getElementById('compass');
if(window.DeviceOrientationEvent) {
 window.addEventListener('deviceorientation', function(event) {
  alpha = event.alpha;
  compass.style.Transform = 'rotate(' + alpha + 'deg)';
 }
}

Any suggestions appreciated.