Animate on Scroll is probably one of the most popular animations libraries made with JavaScript. Again the library is loaded via a CDN:

<!-- CSS, load at the top of your document -->
<link href="https://unpkg.com/aos@2.3.1/dist/aos.css" rel="stylesheet">

<!-- JavaScript, load towards the bottom -->
<script src="https://unpkg.com/aos@2.3.1/dist/aos.js"></script>

<!-- Now initialize AOS -->
<script>
  AOS.init();
</script>