https://www.fmo.nl/ui/fmo-2016/article-templates/homepageHero/homepageHero.js

1require(['domReady'],
2    function (domReady) {
3        'use strict';
4
5        var elements = {};
6
7        var classes = {
8            heroReady: 'at-hero--ready'
9        };
10
11        function init() {
12            elements.hero = document.querySelector('.at-hero');
13            elements.image = document.querySelector('.at-hero__picture');
14
15            if (elements.image) {
16                window.addEventListener('scroll', setNewImagePosition);
17                elements.hero.classList.add(classes.heroReady);
18            }
19        }
20
21        function setNewImagePosition() {
22            var scrollTop = (document.documentElement && document.documentElement.scrollTop) || document.body.scrollTop;
23            elements.image.style.transform = 'translateY(' + Math.round(scrollTop / 3) + 'px)';
24        }
25
26        domReady(init);
27    }
28);