rAFscroll.js

function rAFscroll (fn) {
  const rAF = window.requestAnimationFrame ||
               window.webkitRequestAnimationFrame ||
               window.mozRequestAnimationFrame ||
               window.msRequestAnimationFrame ||
               window.oRequestAnimationFrame ||
               // IE Fallback, you can even fallback to onscroll
               function (callback) { window.setTimeout(callback, 1000 / 60) }

  var lastPosition = -1
  function loop () {
    // Avoid calculations if not needed
    if (lastPosition === window.pageYOffset) {
      rAF(loop)
      return false
    } else lastPosition = window.pageYOffset
    fn()
    rAF(loop)
  }
  loop()
}