GA scroll depth in px

GAscrollDepthPX.js

var scrollDepthtracking = {};
window.addEventListener ('scroll', function () {
    var currentPos = body.scrollTop || window.pageYOffset || document.documentElement.scrollTop,
        currentPosRnd = Math.round((currentPos / 200) * 200);
    if (!scrollDepthtracking[currentPosRnd]) {
        scrollDepthtracking[currentPosRnd] = true;
        ga('b.send', 'event', 'Глубина прокрутки в px', currentPosRnd);
    }
});