scrolldepth.js

var scrollDepthtracking = {}

window.addEventListener('scroll', function () {
  
  var currentPos = body.scrollTop || window.pageYOffset || document.documentElement.scrollTop
      , documentHeight = document.body.offsetHeight
      , windowHeight = window.innerHeight
      , scrollPercent = parseInt((currentPos + 5) / (documentHeight - windowHeight) * 10) * 10
  
  if (!scrollDepthtracking[scrollPercent]) {
    scrollDepthtracking[scrollPercent] = true
    ga('b.send', 'event', 'Глубина прокрутки', scrollPercent)
  }
  
})