scroll-tracking.js

// Add tracking on scroll page
var percents = { 0 :true, 25 :true, 50 :true, 75 :true, 100 :true };

var startTrackOnScroll = function(percent) {
  if(window.analytics) {
    analytics.track('Page Scrolled Percent ' + percent + '%', {
      eventLabel: percent
    });
  }
}

var checkScroll = function(e){
    var scrollTop = $(window).scrollTop();
    var winHeight = $(window).height();
  var docHeight = $(document).height();
  var scrollPercent = (scrollTop) / (docHeight - winHeight);
    var scrollPercentRounded = Math.round(scrollPercent*100);

    //Se o scroll percent estiver no objeto percents
    if( scrollPercentRounded in percents ){
        delete percents[scrollPercentRounded];
        console.log('Page Scrolled Percent ' + scrollPercentRounded + '%')
        startTrackOnScroll(scrollPercentRounded);
    }
    //Se o objeto percents estiver vazio
    if( !Object.keys(percents).length ){
        window.removeEventListener('scroll', checkScroll);
    }
}

window.addEventListener('scroll', checkScroll);