I've been using the above with the following code (Typescript):

            var processingEvent:boolean = false;
            if (window.DeviceOrientationEvent) {
                window.addEventListener('deviceorientation', (data): void=> {
                    if (Math.abs(lastAlpha - data.alpha) < 2) { return; }
                    if (processingEvent) {
                        return;
                    };
                    processingEvent = true;

                    lastAlpha = data.alpha;
                    if (data.absolute === true && data.alpha !== null) {
                        this.deviceOrientation = Math.round(360 - data.alpha);
                        console.log(this.deviceOrientation.toString());
                        this.updateArrows();
                    }
                    processingEvent = false;
                }, false);
            } else {
                alert('DeviceOrienation not supported');
            }

I noticed the event listener could be called again before the routine has finished (the event is raised extremely frequently) so added the 'processing' flag to prevent re-entrancy. It works fine - but it also appeared to work without the check so I'm wondering whether there is any really benefit in it.

Any opinions ?

Side Rant: I've been testing this with different browsers. Firefox gives by far the best results but Chrome, which one would expect to work well on Android devices, is annoyingly flacky....