Google Analytics Scroll Events

const scrh =  document.documentElement,
      scrb =  document.body,
      scrst =  'scrollTop',
      scrsh =  'scrollHeight';
let maxp = 0;
document.addEventListener('scroll', function() {
        const percent = parseInt ( (scrh[scrst]||scrb[scrst]) / ((scrh[scrsh]||scrb[scrsh]) - scrh.clientHeight) * 100);
        if (percent >= 25 && maxp < 25) {
            ga('send', 'event', 'Scrolling', 'moreThan25%', window.location.href, { 'nonInteraction': 1 });
        } else if (percent >= 50 && maxp < 50) {
            ga('send', 'event', 'Scrolling', 'moreThan50%', window.location.href, { 'nonInteraction': 1 });
        } else if (percent >= 75 && maxp < 75) {
            ga('send', 'event', 'Scrolling', 'moreThan75%', window.location.href, { 'nonInteraction': 1 });
        } else if (percent >= 90 && maxp < 90) {
            ga('send', 'event', 'Scrolling', 'moreThan90%', window.location.href, { 'nonInteraction': 1 });
        }
        if (percent > maxp) {
            maxp = percent;
        }
});