main.js

var totalScroll = document.body.scrollHeight - window.innerHeight;

if (window.pageYOffset !== undefined && totalScroll > 0) {
  var johnny = document.getElementById('johnny');

  johnny.style.transform = "translateX(100%)";

  var rollJohnny = function () {
    var top = window.pageYOffset;
    var X = 100 - ((top / totalScroll) * 100);

    johnny.style.transform = "translateX(" + X + "%)";
  };

  window.addEventListener('scroll', rollJohnny);
}