collection.js

document.addEventListener("DOMContentLoaded", function () {
  var $root = document.documentElement;
  var $alo = document.getElementById("alo");
  var $bsaShadow = document.getElementById("bsaShadow");

  var toTravel = $root.scrollHeight - window.innerHeight;
  var fromTop = $alo.offsetTop;
  var menuThrottle = null;

  if ($alo) {
    document.addEventListener("scroll", function (event) {
      var scrollTop = window.scrollY;
      setBsa(scrollTop);
      clearTimeout(menuThrottle);
      throttle = setTimeout(setBsaShadows(scrollTop), 100);
    });

    function setBsaShadows(scrollTop) {
      var distance = toTravel - scrollTop;
      var topFactor = 1 - distance / toTravel;
      $bsaShadow.style.opacity = topFactor;
      $bsaShadow.style.transform = "scaleY(" + topFactor + ")";
    }

    function setBsa(scrollTop) {
      if (scrollTop >= fromTop) {
        $alo.classList.add("is-fixed");
      } else {
        $alo.classList.remove("is-fixed");
      }
    }

    setBsaShadows(0);
  }

  // Hashes
  var $hashes = document.querySelectorAll(".hash, .menu-list-ul li a");

  Array.prototype.forEach.call($hashes, function ($el) {
    $el.addEventListener("click", function (event) {
      event.preventDefault();
      var propertyName = $el.dataset.propertyName;
      var $target = document.getElementById($el.dataset.propertyName);
      history.replaceState("", document.title, "#" + propertyName);

      if ($target) {
        $target.scrollIntoView();
      }
    });
  });
});