derpyherp/javascript-banner-rotator.js

## javascript-banner-rotator.js
//probably want a window width of at least 468px to display a 468x60 banner
if (window.matchMedia("(min-width: 468px)").matches) {
  var banner;
	//the first number should equal the number of banners
	switch(Math.floor((Math.random() * 3) + 1)) {
		case 1:
			banner = ["https://destination1.com", "https://destination1.com/banner.gif"];
			break;
		case 2:
			banner = ["https://destination2.com", "https://destination2.com/banner.png"];
			break;
		default:
			banner = ["https://destination3.com", "https://destination3.com/banner.jpg"];
	}
	if (banner) {
		document.getElementById('banner-container').innerHTML = '<a href="'+banner[0]+'" target="_blank" rel="nofollow noopener noreferrer"><img src="'+banner[1]+'" height="468" width="60" alt="Advertisement" /></a>';
	}
}

## z-example.html
<!DOCTYPE html>
<html lang="en">
<head></head>
<body>
	<div id="banner-container" style="width:468px;height:60px;></div>
	<script src="javascript-banner-rotator.js" async></script>
</body>
</html>
	<!DOCTYPE html>
	<html lang="en">
	<head></head>
	<body>
	<div id="banner-container" style="width:468px;height:60px;></div>
	<script src="javascript-banner-rotator.js" async></script>
	</body>
	</html>