GSAP (GreenSock) — Web Animation Skill

When to use

• High-quality UI/motion design: entrances, micro-interactions, page transitions
• Timeline-based sequences (vs. scattered CSS transitions)
• Scroll-driven storytelling (with ScrollTrigger)
• Complex easing, staggering, orchestration across many elements

Key concepts & APIs

• Tweens:
  • gsap.to(targets, vars)
  • gsap.from(targets, vars)
  • gsap.fromTo(targets, fromVars, toVars)
• Timelines:
  • const tl = gsap.timeline({ defaults, repeat, yoyo, paused })
  • Chain: tl.to(...).from(...).addLabel('x').add(() => ...)
  • Position parameter: absolute 1.2, relative "+=0.5", overlap "-=0.3", label "intro"
• Eases: ease: "power2.out", "expo.inOut", "elastic.out(1, 0.3)"
• Staggers: stagger: 0.05 or { each, from: "start|center|end|random", grid }
• Performance-friendly properties:
  • Prefer transforms (x, y, scale, rotation) and opacity (autoAlpha)
• ScrollTrigger (plugin):
  • gsap.registerPlugin(ScrollTrigger)
  • Inline: gsap.to(".box", { scrollTrigger: ".box", x: 500 })
  • Advanced: scrollTrigger: { trigger, start, end, scrub, pin, snap, markers }

Common pitfalls (and fixes)

• Animating layout properties (top/left/width/height) → jank → Use transforms
• ScrollTrigger "not firing" → Ensure trigger has height, check scroll container
• Not cleaning up in SPA/React → Use gsap.context() and revert on unmount
• FOUC → Initialize after layout is stable; ScrollTrigger.refresh() after images load

Quick recipes

1) Hero entrance (stagger)

gsap.from(".hero [data-anim]", {
  y: 24, autoAlpha: 0, duration: 0.8,
  ease: "power2.out", stagger: 0.06,
});

2) Sequenced timeline

const tl = gsap.timeline({ defaults: { ease: "power2.out", duration: 0.6 } });
tl.from(".nav", { y: -20, autoAlpha: 0 })
  .from(".hero-title", { y: 30, autoAlpha: 0 }, "-=0.2")
  .from(".hero-cta", { scale: 0.95, autoAlpha: 0 }, "-=0.2");

3) Scroll-scrub pinned section

gsap.registerPlugin(ScrollTrigger);
gsap.timeline({
  scrollTrigger: { trigger: ".story", start: "top top", end: "+=800", scrub: 1, pin: true },
}).to(".story .panel", { xPercent: -200 });

Tips for AI Agents

• Ask whether this is a static site or SPA (React/Next/Vue) for cleanup patterns.
• Confirm if scroll-driven sections are needed (pin/scrub/snap).
• Always consider prefers-reduced-motion for accessibility.