GSAP Vanilla

mount → initial state → intro → settled → outro → end state → unmount

On full document loads, the browser owns mount and unmount; animation owns the five phases between them. On same-document swaps, the router owns node replacement and persistent resources need explicit cleanup.

Keep the requested look and existing project conventions. Add GSAP/plugins only as needed; do not replace the chosen animation library unless asked.

This skill decides when motion runs. For what moves, and for a feel such as premium or playful, also load the animaxxing skill when it is installed: its recipes and its guide to finding the vibe plug into this lifecycle.

Start with the project

Read repository instructions, existing animation, layouts, navigation, CSS, accessibility conventions, and checks. Then:

1. Find out how pages are produced: hand-written HTML, a static generator with no client framework, a bundler such as Vite with no UI framework, or a transition library such as Swup, Barba, or Taxi. If a component framework renders the pages, say this skill does not cover it and use that framework's skill.
2. Find out how GSAP loads: npm import, import map, or script tag. Keep it.
3. Find out how scripts run: inline, defer, or type="module". This decides when the DOM exists and whether the page can paint before the script runs.
4. Check the target browsers. Cross-document View Transitions, pageswap and pagereveal, the Navigation API, and blocking="render" are not everywhere. Read installed transition-library docs/types and feature-detect browser APIs instead of trusting memory, and make sure the site works with all of them missing.

Pick a navigation model

Identify the navigation model before writing lifecycle code. Assign one owner per navigation; a same-document router may still need a full-load fallback.

• Full document loads. Every link replaces the document. The outro plays before the link is followed; the intro plays when the new page loads. This is the default and needs no router.
• Full document loads with cross-document View Transitions. The browser snapshots the old page and animates to the new one. GSAP fills in what a snapshot pair cannot do.
• Same-document navigation. Script fetches the next page and swaps content in place, so chrome, state, and timelines survive. Use a maintained library unless the project already owns a router or has a reason to. See Same-document navigation.

Choose the engine

Use cross-document View Transitions for snapshot morphs or page crossfades, with an instant-swap fallback. Use GSAP for live-DOM outros that gate navigation, interruptible sequences, split text, or scroll-linked motion. One engine per element; see combining engines.

Read only what you need

• Invisible entrances, failed initialization, indexing, and first-load performance: Initialization and recovery, plus the framework integration.
• First paint, script timing, fonts, navigation type, prerendering, the bfcache, hidden tabs, and leaving a page with an outro: Page load and unload.
• @view-transition, pageswap, pagereveal, types, render blocking, and handing off between the browser and GSAP: Cross-document navigation.
• Fetch and swap routers, link interception, history, scroll, focus, script re-execution, and when to use a library: Same-document navigation.
• The five phases, GSAP setup, contexts, show and hide, layout stability, scroll, text, plugins: Lifecycle implementation.
• Lenis, ScrollSmoother, or eased page scrolling across documents and swaps: Smooth scrolling, plus per-document scrollers and one scroller under a swap router.
• Curtains, first-visit preloaders, and shared-element morphs: Transition archetypes, plus the full-document and same-document integration.
• Touch, viewport changes, and device budgets: Devices and input.
• Tauri, Electron, or Wails desktop shells: Desktop webviews.
• Before calling work done: Verification.

Install the official GSAP skills alongside this repository. Load gsap-core for API details and the relevant plugin skill only as needed.

Rules

• Preserve invisible intros on successful setup; recover the current incoming owner on failure. Follow the initialization contract before adding hiding rules.
• GSAP runs after the DOM it targets exists. Scope selectors with gsap.context to the page or component root. Clean up every tween, trigger, split, and listener when its owner goes away.
• Reserve final geometry with normal CSS and a stable wrapper; overlap outgoing/incoming content without doubling layout space.
• Set initial values before first paint, then reveal. Successful initialization never flashes settled content before the intro, and never a blank page without JavaScript.
• Clear temporary styles at settled. Use will-change only while animating; this overrides gsap-performance's static hint.
• Use capability queries for device tiers. Touch states release; controls work without hover.
• Keep outgoing content in the DOM and visible through outro and end state. Follow the link, remove the node, or swap only from the end callback.
• Back and forward never run an outro. A fresh document reached by history gets an intro-only path, and a bfcache restore gets no intro at all.
• A prerendered page sets initial state at once and waits for activation before it animates.
• Keep native link behavior, focus, scroll restoration, and no-JavaScript readability.
• Never add unload or beforeunload listeners for animation. They disable the bfcache. Use pagehide.
• Reduced motion reaches the same settled state and still fires every completion callback.
• Define interruption and rapid-click behavior; completion must release navigation waits exactly once.
• Verify in a real browser when practical, including reload, back, forward, and a click from a background tab.