Horizontal and Vertical Parallax Effect JavaScript Library

Here is a micro-library for adding the parallax effect to background images. This library is compatible with all browsers including Internet Explorer 11. This file minfies to less than a kilobyte.

Combine with the Animate on Scroll JavaScript Library for more special effects.

Using the parallax effect library requires that the class parallax-effect be added to each HTML element that will be affected. Optionally, the background-parallax-ratio can be used to control the speed of the effect. Set this to 1 and the background does not move. If using background-attachment: fixed; CSS property and value then specify it inline and not in the CSS file or style tag. Note that iOS is not friendly to fixed backgrounds. Another attribute is the background-position-x which sets that CSS property. It defaults to 50% (centered).

NEW: define the function that will be used as a callback to use to adjust the backgrounds or move elements as the user scrolls be it horizontally or vertically. The element's attribute that must be defined is parallax-function and this function must be in the window namespace.

IMPORTANT: the header X-XSS-Protection must be added to the HTTP server with a value of 0 for this to work properly on Safari (iOS and Macintosh) browsers when the parallax-effect.js file is not loaded through a local URL.

Here is the code for this simple library.

(function () {
	var w = window, callFunc = function () {
		var divs = document.getElementsByClassName("parallax-effect");
		for (var i = 0; i < divs.length; i++) {
			var o = divs[i], y = (function () {
				if (w.pageYOffset) {
					return w.pageYOffset;
				}
				else {
					var d = document;
					if (d.documentElement.scrollTop == 0) {
						return d.body.scrollTop;
					}
					else {
						return d.documentElement.scrollTop;
					}
				}
			})() - (o.offsetTop || 0), funcname = o.getAttribute("parallax-function");
			if (funcname) {
				if (typeof w[funcname] == "function") {
					w[funcname](y, o);
				}
				else {
					console.log("window." + funcname + " is not a function");
				}
			}
			else {
				var ratio = parseFloat(o.getAttribute("background-parallax-ratio") || 0.5);
				if (isNaN(ratio)) {
					ratio = 0.5;
				}
				y *= (o.style.backgroundAttachment == "fixed" ? 0 : 1) - ratio;
				o.style.backgroundPosition = (o.getAttribute("background-position-x") || "50%") + " " + Math.round(y) + "px";
			}
		}
	}, addHandler = function (type) {
		if (w.addEventListener) {
			w.addEventListener(type, callFunc, false);
		} else if (w.attachEvent) {
			w.attachEvent("on" + type, callFunc);
		} else {
			w["on" + type] = callFunc;
		}
		};
	addHandler("load");
	addHandler("resize");
	addHandler("scroll");
	addHandler("deviceorientation");
	addHandler("devicemotion");
})();

Here is example code using this library.

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>PARALLAX EFFECT - VERSION 2</title>
	<style>
	*,
	*::before,
	*::after {
		box-sizing: border-box;
	}
	body {
		margin: 0;
		padding: 0;
		font-family: sans-serif;
		background-color: black;
		color: white;
	}
	h1 {
		font-size: 3vmax;
	}
	p {
		font-size: 1vmax;
	}
	.page {
		width: 100%;
		height: 100vh;
		display: flex;
		flex-direction: column;
		justify-content: center;
		align-items: center;
		overflow: hidden;
	}
	.scene-1 {
		background-image: url(https://picsum.photos/id/1044/1920/1080);
		background-size: cover;
		background-repeat: no-repeat;
	}
	.scene-2,
	.scene-3 {
		position: relative;
		background-image: url(http://www.prowaretech.com/img/beach.png), url(http://www.prowaretech.com/img/mountain.png), url(http://www.prowaretech.com/img/moon.png), url(http://www.prowaretech.com/img/stars.jpg);
		background-size: cover;
		background-repeat: no-repeat;
	}
	.scene-3::after {
		content: "";
		position: absolute;
		top: 0;
		left: 0;
		right: 0;
		bottom: 0;
		background-color: slategray;
		mix-blend-mode: color;
	}
	</style>
</head>
<body>
	
	<div class="page"><h1>ACME</h1><h1>About Us</h1><p>SCROLL DOWN</p></div>

	<div class="parallax-effect page scene-1"><h1>plain parallax effect</h1></div>

	<div class="page"><h1>Products</h1><p>SCROLL DOWN MORE</p></div>

	<div class="parallax-effect page scene-2" parallax-function="shift"><h1>parallax effect with multiple images &amp; horizontal slide</h1></div>

	<div class="page"><h1>Services</h1><p>KEEP SCROLLING</p></div>

	<div class="parallax-effect page scene-3" parallax-function="shift"></div>

	<div class="page"><h1>Support</h1><p>END</p></div>

<script type="text/javascript">
function windowWidth(){
	if(window.innerWidth)
		return window.innerWidth;
	else if(document.documentElement.clientWidth == 0){
		return document.body.clientWidth;
	else
		return document.documentElement.clientWidth;
}
function shift(position, element) {
	var beachY = Math.round(position * 0.3), // the decimals here are the ratio, 0 would leave the image still (no parallax effect)
	mountainY = Math.round(position * 0.5),
	moonX = Math.round(position * 0.8 + windowWidth() / 4), // this is being applied to the X coordinate and the value of 0.8 is used to slow down the movement of the moon
	moonY = Math.round(position * 0.2),
	starsY = Math.round(position * 0.9);
	element.style.backgroundPosition = "50% " + beachY + "px, 50% " + mountainY + "px, " + moonX + "px " + moonY + "px, 50% " + starsY + "px";
}
</script>

<script src="http://www.prowaretech.com/js/parallax-effect.min.js"></script><!-- ALWAYS LOAD THIS LIBRARY AT THE END OF THE HTML DOCUMENT -->

</body>
</html>

Coding Video

https://youtu.be/9teZeYFXUU8