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.
name: 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>
/*
Sequence animation on scroll when visible. Requires Animation Keyframe. Usage:
1) Insert this code in the <head> along with the Animation Keyframe code.
2) Add to Tailwind Classes: [animation:animationIn_0.8s_ease-out_0.1s_both] animate-on-scroll
*/
(function () {
// Inject CSS for paused/running states
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); // observing twice is a no-op
});
};
document.addEventListener("DOMContentLoaded", () => initInViewAnimations());
})();
</script>