Web-Slinger.css: Like Wow.js But With CSS-y Scroll Animations
Can we recreate a JavaScript library for scrolling animations with a modern CSS approach using CSS Scroll-Driven Animations? Yes. Yes, we can. Web-Slinger.css: Like Wow.js But With CSS-y Scroll Animations originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
We had fun in my previous article exploring the goodness of scrolly animations supported in today’s versions of Chrome and Edge (and behind a feature flag in Firefox for now). Those are by and large referred to as “scroll-driven” animations. However, “scroll triggering” is something the Chrome team is still working on. It refers to the behavior you might have seen in the wild in which a point of no return activates a complete animation like a trap after our hapless scrolling user ventures past a certain point. You can see JavaScript examples of this on the Wow.js homepage which assembles itself in a sequence of animated entrances as you scroll down. There is no current official CSS solution for scroll-triggered animations — but Ryan Mulligan has shown how we can make it work by cleverly combining the animation-timeline property with custom properties and style queries.
That is a very cool way to combine new CSS features. But I am not done being overly demanding toward the awesome emergent animation timeline technology I didn’t know existed before I read up on it last month. I noticed scroll timelines and view timelines are geared toward animations that play backward when you scroll back up, unlike the Wow.js example where the dogs roll in and then stay. Bramus mentions the same point in his exploration of scroll-triggered animations. The animations run in reverse when scrolling back up. This is not always feasible.
As a divorced Dad, I can attest that the Tinder UI is another example of a pattern in which scrolling and swiping can have irreversible consequences.
Scroll till the cows come home with Web-Slinger.css
Believe it or not, with a small amount of SCSS and no JavaScript, we can build a pure CSS replacement of the Wow.js library, which I hereby christen “Web-Slinger.css.” It feels good to use the scroll-driven optimized standards already supported by some major browsers to make a prototype library. Here’s the finished demo and then we will break down how it works. I have always enjoyed the deliberately lo-fi aesthetic of the original Wow.js page, so it’s nice to have an excuse to create a parody. Much profession, so impress.
Teach scrolling elements to roll over and stay
Web-Slinger.css introduces a set of class names in the format .scroll-trigger-n and .on-scroll-trigger-n. It also defines --scroll-trigger-n custom properties, which are inherited from the document root so we can access them from any CSS class. These conventions are more verbose than Wow.js but also more powerful. The two types of CSS classes decouple the triggers of our one-off animations from the elements they trigger, which means we can animate anything on the page based on the user reaching any scroll marker.
Here’s a basic example that triggers the Animate.css animation “flipInY” when the user has scrolled to the A more advanced use is the sticky “Cownter” (trademark pending) at the top of the demo page, which takes advantage of the ability of one trigger to activate an arbitrary number of animations anywhere in the document. The Cownter increments as new cows appear then displays a reset button once we reach the final scroll trigger at the bottom of the page.
Here is the markup for the Cownter:
.scroll-trigger-8.
