https://shortify.pro/js/plugins/parallax.min.js

1var windowHeight = window.innerHeight;
2
3document.addEventListener('resize', function() {
4	windowHeight = window.innerHeight;
5})
6
7function outerHeight(el) {
8	var height = el.offsetHeight;
9	var style = getComputedStyle(el);
10
11	height += parseInt(style.marginTop) + parseInt(style.marginBottom);
12	return height;
13}
14
15function parallax (el, speedFactor, outerHeight) {
16	var foo = document.querySelectorAll(el);
17
18	var getHeight;
19	var firstTop;
20	var paddingTop = 0;
21
22	//get the starting position of each element to have parallax applied to it
23	foo.forEach(function(subEl){
24	    firstTop = subEl.getBoundingClientRect().top;
25	});
26
27	if (outerHeight) {
28		getHeight = function(el) {
29			return outerHeight(el);
30		};
31	} else {
32		getHeight = function(el) {
33			return el.clientHeight;
34		};
35	}
36
37	// function to be called whenever the window is scrolled or resized
38	function update(){
39		var pos = window.scrollY;
40
41		foo.forEach(function(subEl){
42			var element = subEl;
43			var top = element.getBoundingClientRect().top;
44			var height = getHeight(element);
45
46			element.style.top = -(Math.round((firstTop - pos) * speedFactor)) + "px";
47		});
48	}
49	document.addEventListener('scroll', update, true)
50	document.addEventListener('resize', update)
51	update()
52};
53
54parallax(".hero", -0.6);