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 }
• Standalone: ScrollTrigger.create({ trigger, start, end, onUpdate, onToggle })

Common pitfalls (and fixes)

• Animating layout properties (top/left/width/height) → jank
• Use transforms, add will-change: transform, avoid forced reflow.
• ScrollTrigger “not firing” due to wrong trigger sizing/overflow containers
• Ensure trigger exists, has height, and check scroll container (nested scrolling needs config).
• Not cleaning up in SPA/React
• Use gsap.context() and revert on unmount; kill triggers (ScrollTrigger.getAll().forEach(t => t.kill())) if needed.
• FOUC / measuring before fonts/images load
• Initialize after layout is stable; run ScrollTrigger.refresh() after images load.

Quick recipes

1) Hero entrance (stagger)

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

2) Sequenced timeline

js
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

js
gsap.registerPlugin(ScrollTrigger);

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

What to ask the user (if requirements unclear)

• Is this a static site or SPA (React/Next/Vue)? Any page transitions?
• Do we need scroll-driven sections (pin/scrub/snap)?
• Performance constraints (mobile support, reduced motion)?