| name | web-animation-on-scroll |
| description | Create an on-scroll animation trigger using IntersectionObserver with Tailwind-friendly animation classes and keyframes. Use when asked for scroll-reveal, animate-on-scroll, or sequencing element animations when they enter the viewport. |
Animation On Scroll Skill
Workflow
- Confirm animation style, timing, and whether animations should run once or repeat.
- Provide the keyframes + JS observer snippet and the exact Tailwind class to apply.
- Offer focused tweaks only (threshold, rootMargin, duration, delay, transform/blur values).
Usage checklist
- Insert the JS snippet in the
<head> after the keyframes.
- Add the animation class and
animate-on-scroll to elements.
- Ensure your keyframes name matches the Tailwind animation reference.
IntersectionObserver trigger
<script>
(function () {
const style = document.createElement("style");
style.textContent = `
/* Default: paused */
.animate-on-scroll { animation-play-state: paused !important; }
/* Activated by JS */
.animate-on-scroll.animate { animation-play-state: running !important; }
`;
document.head.appendChild(style);
const once = true;
if (!window.__inViewIO) {
window.__inViewIO = new IntersectionObserver((entries) => {
entries.forEach((entry) => {
if (entry.isIntersecting) {
entry.target.classList.add("animate");
if (once) window.__inViewIO.unobserve(entry.target);
}
});
}, { threshold: 0.2, rootMargin: "0px 0px -10% 0px" });
}
window.initInViewAnimations = function (selector = ".animate-on-scroll") {
document.querySelectorAll(selector).forEach((el) => {
window.__inViewIO.observe(el);
});
};
document.addEventListener("DOMContentLoaded", () => initInViewAnimations());
})();
</script>
Keyframes
<style>
@keyframes animationIn {
0% {
opacity: 0;
transform: translateY(30px);
filter: blur(8px);
}
100% {
opacity: 1;
transform: translateY(0);
filter: blur(0px);
}
}
</style>
Tailwind example
<div class="animate-on-scroll [animation:animationIn_0.8s_ease-out_0.1s_both]">
...
</div>
Customization knobs
- Trigger: adjust
threshold and rootMargin for earlier/later reveals.
- Repeat: set
once = false to allow replays when re-entering.
- Motion: tweak
translateY and blur in keyframes.
- Timing: change duration and delay in the Tailwind animation value.
Common pitfalls
- Forgetting to include the keyframes before the JS snippet.
- Using a different keyframe name than in the Tailwind animation.
- Animations not running because the element is already in view before observer init.
Questions to ask when specs are missing
- Should animations run once or every time the element re-enters?
- How far before entering the viewport should they start?
- What motion style (fade, slide, blur, scale) do you want?
