Edit in JSFiddle

function autoScroll() {
        var elapsed, delta;

        if (amplitude) {
            elapsed = Date.now() - timestamp;
            delta = -amplitude * Math.exp(-elapsed / timeConstant);
            if (delta > 5 || delta < -5) {
                scroll(target + delta);
                requestAnimationFrame(autoScroll);
            } else {
                scroll(target);
            }
        }
    }