模式簡單

GSAP Accordion

Three accordion variants (exclusive, multi-open, minimal) using GSAP height:'auto' animation. Demonstrates smooth open/close without CSS max-height artifacts, arrow rotation spring ease, and aria attributes.

在 Lab 開啟

gsap accordion height-auto a11y

目標: JS HTML

程式碼

/* ── Demo 50: GSAP Accordion ── */
/* Clean light-ish neutral palette — distinct from all existing dark demos */

:root {
  --bg: #f8f7f4;
  --white: #ffffff;
  --panel: #f0ede8;
  --border: #d8d4cc;
  --text: #1a1814;
  --muted: #7a756c;
  --accent: #2d5be3; /* electric blue */
  --accent-warm: #e05a20;
  --green: #1a7a40;
}

*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: "DM Sans", -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
  line-height: 1.6;
}

.label {
  display: block;
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 1rem;
}

code {
  font-family: "SF Mono", "Fira Code", monospace;
  font-size: 0.78rem;
  color: var(--accent);
  background: rgba(45, 91, 227, 0.08);
  padding: 0.15em 0.4em;
  border-radius: 3px;
}

/* ── Page layout ── */
.page {
  max-width: 820px;
  margin: 0 auto;
  padding: 5rem 2rem 8rem;
}

.page-header {
  margin-bottom: 5rem;
  padding-bottom: 3rem;
  border-bottom: 1px solid var(--border);
}

.page-header h1 {
  font-size: clamp(3rem, 7vw, 5.5rem);
  font-weight: 700;
  line-height: 1.0;
  letter-spacing: -0.03em;
  margin-bottom: 1.5rem;
  color: var(--text);
}

.page-header h1 em {
  font-style: normal;
  color: var(--accent);
}

.page-header p {
  font-size: 1rem;
  color: var(--muted);
  line-height: 1.8;
  max-width: 540px;
}

/* ── Demo sections ── */
.demo-section {
  margin-bottom: 4.5rem;
}

.demo-label {
  display: flex;
  align-items: baseline;
  gap: 1rem;
  margin-bottom: 1.25rem;
}

.variant-tag {
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  padding: 0.2rem 0.6rem;
  background: var(--accent);
  color: white;
  border-radius: 2px;
}

.demo-label h2 {
  font-size: 1.05rem;
  font-weight: 500;
  color: var(--muted);
}

/* ── Accordion base ── */
.accordion {
  border: 1px solid var(--border);
  border-radius: 4px;
  overflow: hidden;
  background: var(--white);
}

.acc-item {
  border-bottom: 1px solid var(--border);
}

.acc-item:last-child {
  border-bottom: none;
}

/* ── Trigger ── */
.acc-trigger {
  width: 100%;
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 1.25rem 1.5rem;
  background: transparent;
  border: none;
  cursor: pointer;
  text-align: left;
  color: var(--text);
  font-family: "DM Sans", sans-serif;
  font-size: 0.95rem;
  font-weight: 500;
  transition: background 0.2s;
}

.acc-trigger:hover {
  background: var(--panel);
}

.at-icon {
  color: var(--accent);
  font-size: 0.5rem;
  flex-shrink: 0;
  transition: color 0.3s;
}

.at-num {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--muted);
  letter-spacing: 0.06em;
  flex-shrink: 0;
  width: 24px;
}

.at-title {
  flex: 1;
}

.at-arrow {
  flex-shrink: 0;
  color: var(--muted);
  font-size: 0.9rem;
  transition: transform 0.35s cubic-bezier(0.34, 1.56, 0.64, 1);
}

/* Active state */
.acc-item[data-open="true"] .acc-trigger,
.acc-item.acc-item--open .acc-trigger {
  background: var(--panel);
}

.acc-item[data-open="true"] .at-icon,
.acc-item.acc-item--open .at-icon {
  color: var(--accent-warm);
}

.acc-item[data-open="true"] .at-arrow,
.acc-item.is-open .at-arrow {
  transform: rotate(180deg);
}

/* ── Body ── */
.acc-body {
  overflow: hidden;
  height: 0;
}

.acc-item[data-open="true"] .acc-body,
.acc-item.acc-item--open .acc-body {
  height: auto;
}

.acc-inner {
  padding: 0 1.5rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.8rem;
}

.acc-inner p {
  font-size: 0.9rem;
  color: var(--muted);
  line-height: 1.8;
}

/* Timeline variant */
.acc-inner--timeline {
  padding-top: 0.5rem;
}

.tl-item {
  display: grid;
  grid-template-columns: 90px 1fr;
  gap: 1rem;
  padding: 0.7rem 0;
  border-bottom: 1px solid var(--panel);
}

.tl-item:last-child {
  border-bottom: none;
}

.tl-week {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.04em;
  padding-top: 2px;
}

.tl-task {
  font-size: 0.88rem;
  color: var(--text);
}

/* ── Minimal variant ── */
.accordion--minimal {
  border: none;
  border-radius: 0;
  border-top: 2px solid var(--text);
}

.accordion--minimal .acc-item {
  border-bottom: 1px solid var(--border);
}

.accordion--minimal .acc-trigger {
  padding: 1.25rem 0;
  font-size: 1.05rem;
  font-weight: 700;
}

.accordion--minimal .acc-trigger:hover {
  background: transparent;
  color: var(--accent);
}

.accordion--minimal .acc-trigger:hover .at-arrow {
  color: var(--accent);
}

.accordion--minimal .at-arrow {
  font-size: 1.2rem;
  font-weight: 300;
  color: var(--text);
  transition: transform 0.35s cubic-bezier(0.34, 1.56, 0.64, 1), color 0.2s;
}

.accordion--minimal .is-open .at-arrow {
  transform: rotate(45deg);
}

.accordion--minimal .acc-inner {
  padding-left: 0;
}

/* ── Responsive ── */
@media (max-width: 640px) {
  .page {
    padding: 3rem 1.25rem 5rem;
  }
  .demo-label {
    flex-direction: column;
    gap: 0.5rem;
  }
}

/* ── Reduced motion ── */
html.reduced-motion .acc-trigger,
html.reduced-motion .at-arrow {
  transition: none !important;
}

if (!window.MotionPreference) {
  const __mql = window.matchMedia("(prefers-reduced-motion: reduce)");
  const __listeners = new Set();

  const MotionPreference = {
    prefersReducedMotion() {
      return __mql.matches;
    },
    setOverride(value) {
      const reduced = Boolean(value);
      document.documentElement.classList.toggle("reduced-motion", reduced);
      window.dispatchEvent(new CustomEvent("motion-preference", { detail: { reduced } }));
      for (const listener of __listeners) {
        try {
          listener({ reduced, override: reduced, systemReduced: __mql.matches });
        } catch {}
      }
    },
    onChange(listener) {
      __listeners.add(listener);
      try {
        listener({
          reduced: __mql.matches,
          override: null,
          systemReduced: __mql.matches,
        });
      } catch {}
      return () => __listeners.delete(listener);
    },
    getState() {
      return { reduced: __mql.matches, override: null, systemReduced: __mql.matches };
    },
  };

  window.MotionPreference = MotionPreference;
}

function prefersReducedMotion() {
  return window.MotionPreference.prefersReducedMotion();
}

function initDemoShell() {
  // No-op shim in imported standalone snippets.
}

import gsap from "gsap";
import { ScrollTrigger } from "gsap/ScrollTrigger";

gsap.registerPlugin(ScrollTrigger);

initDemoShell({
  title: "GSAP Accordion",
  category: "css-canvas",
  tech: ["gsap", "height-auto", "spring-ease", "a11y"],
});

const reduced = prefersReducedMotion();
if (reduced) document.documentElement.classList.add("reduced-motion");

// ── Core accordion logic ──────────────────────────────────────────────────────
// duration and ease shared across all variants
const DURATION = reduced ? 0 : 0.45;
const EASE_OPEN = "expo.out";
const EASE_CLOSE = "expo.in";

/**
 * Open a panel
 * @param {HTMLElement} item  - .acc-item
 * @param {boolean} instant  - skip animation (reduced motion)
 */
function openPanel(item, instant = false) {
  const body = item.querySelector(".acc-body");
  const trigger = item.querySelector(".acc-trigger");
  const arrow = trigger.querySelector(".at-arrow");

  item.classList.add("is-open");
  trigger.setAttribute("aria-expanded", "true");

  if (instant) {
    gsap.set(body, { height: "auto", overflow: "hidden" });
  } else {
    gsap.to(body, {
      height: "auto",
      duration: DURATION,
      ease: EASE_OPEN,
      overwrite: true,
      onStart: () => {
        body.style.overflow = "hidden";
      },
    });
    gsap.to(arrow, {
      rotation: 180,
      duration: DURATION * 0.8,
      ease: "back.out(2)",
      overwrite: true,
    });
  }
}

/**
 * Close a panel
 * @param {HTMLElement} item  - .acc-item
 * @param {boolean} instant  - skip animation
 */
function closePanel(item, instant = false) {
  const body = item.querySelector(".acc-body");
  const trigger = item.querySelector(".acc-trigger");
  const arrow = trigger.querySelector(".at-arrow");

  item.classList.remove("is-open");
  trigger.setAttribute("aria-expanded", "false");

  if (instant) {
    gsap.set(body, { height: 0 });
  } else {
    gsap.to(body, {
      height: 0,
      duration: DURATION * 0.8,
      ease: EASE_CLOSE,
      overwrite: true,
    });
    gsap.to(arrow, {
      rotation: 0,
      duration: DURATION * 0.6,
      ease: "power2.in",
      overwrite: true,
    });
  }
}

// ── Initialize each accordion ─────────────────────────────────────────────────
document.querySelectorAll(".accordion").forEach((accordion) => {
  const mode = accordion.dataset.mode; // 'exclusive' | 'multi'
  const items = accordion.querySelectorAll(".acc-item");

  // Set initial state — items marked open start open, rest start closed
  items.forEach((item) => {
    const body = item.querySelector(".acc-body");
    const isInitiallyOpen =
      item.classList.contains("acc-item--open") || item.hasAttribute("data-open");

    if (isInitiallyOpen) {
      gsap.set(body, { height: "auto", overflow: "hidden" });
      item.classList.add("is-open");
      const trigger = item.querySelector(".acc-trigger");
      const arrow = trigger.querySelector(".at-arrow");
      if (arrow) gsap.set(arrow, { rotation: 180 });
      trigger.setAttribute("aria-expanded", "true");
    } else {
      gsap.set(body, { height: 0, overflow: "hidden" });
    }

    // Click handler
    item.querySelector(".acc-trigger").addEventListener("click", () => {
      const isOpen = item.classList.contains("is-open");

      if (mode === "exclusive") {
        // Close all other open items first
        items.forEach((other) => {
          if (other !== item && other.classList.contains("is-open")) {
            closePanel(other, reduced);
          }
        });
      }

      if (isOpen) {
        closePanel(item, reduced);
      } else {
        openPanel(item, reduced);
      }
    });
  });
});

// ── Minimal variant: arrow rotates to + / × ──────────────────────────────────
// The minimal accordion uses '+' which rotates to '×' on open
// This is already handled by the rotation tween in openPanel/closePanel

// ── Entrance animations ───────────────────────────────────────────────────────
if (!reduced) {
  gsap.set(".page-header > *", { opacity: 0, y: 16 });
  gsap.to(".page-header > *", {
    opacity: 1,
    y: 0,
    duration: 0.7,
    stagger: 0.1,
    ease: "expo.out",
    delay: 0.3,
  });

  document.querySelectorAll(".demo-section").forEach((sec, i) => {
    gsap.set(sec, { opacity: 0, y: 24 });
    gsap.to(sec, {
      opacity: 1,
      y: 0,
      duration: 0.8,
      ease: "expo.out",
      scrollTrigger: {
        trigger: sec,
        start: "top 78%",
        toggleActions: "play none none reverse",
      },
    });
  });
}

// ── Motion toggle ─────────────────────────────────────────────────────────────
window.addEventListener("motion-preference", (e) => {
  gsap.globalTimeline.paused(e.detail.reduced);
});

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>GSAP Accordion</title>
  <link rel="preconnect" href="https://fonts.googleapis.com">
  <link href="https://fonts.googleapis.com/css2?family=DM+Sans:wght@300;400;500;700&display=swap" rel="stylesheet">
  <link rel="stylesheet" href="style.css">
    <script type="importmap">{"imports":{"gsap":"https://esm.sh/[email protected]","gsap/ScrollTrigger":"https://esm.sh/[email protected]/ScrollTrigger","gsap/SplitText":"https://esm.sh/[email protected]/SplitText","gsap/Flip":"https://esm.sh/[email protected]/Flip","gsap/ScrambleTextPlugin":"https://esm.sh/[email protected]/ScrambleTextPlugin","gsap/TextPlugin":"https://esm.sh/[email protected]/TextPlugin","gsap/all":"https://esm.sh/[email protected]/all","gsap/":"https://esm.sh/[email protected]/","lenis":"https://esm.sh/[email protected]/dist/lenis.mjs","three":"https://esm.sh/[email protected]","three/addons/":"https://esm.sh/[email protected]/examples/jsm/"}}</script>
</head>
<body>

  <div class="page">

    <header class="page-header">
      <span class="label">Technique Demo</span>
      <h1>GSAP <em>Accordion</em></h1>
      <p>Height animation from <code>0 → auto</code> using GSAP's height tweening. Each panel collapses and expands with spring easing. Multiple variants: exclusive, multi-open, and nested.</p>
    </header>

    <!-- Variant 1: Exclusive (one open at a time) -->
    <section class="demo-section">
      <div class="demo-label">
        <span class="variant-tag">Variant A</span>
        <h2>Exclusive — one open at a time</h2>
      </div>
      <div class="accordion" id="acc-exclusive" data-mode="exclusive">
        <div class="acc-item" data-open="true">
          <button class="acc-trigger" aria-expanded="true">
            <span class="at-icon">◆</span>
            <span class="at-title">What is GSAP accordion animation?</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>A GSAP accordion animates panel height from <code>0</code> to its natural content height using <code>gsap.to(el, { height: 'auto' })</code>. Unlike CSS transitions which can't animate from <code>height: 0</code> to <code>height: auto</code>, GSAP handles this seamlessly by calculating the target height internally.</p>
              <p>The key is pairing <code>overflow: hidden</code> on the container with a GSAP tween that toggles <code>autoAlpha</code> and <code>height</code> together for a smooth reveal.</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-icon">◆</span>
            <span class="at-title">How do you animate height: auto?</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>GSAP's <code>gsap.to(el, { height: 'auto', duration: 0.5 })</code> works by measuring the element's scrollHeight at tween start, then animating from current to that value. Combine with <code>ease: 'expo.out'</code> for a natural deceleration.</p>
              <p>To collapse, use <code>gsap.to(el, { height: 0 })</code> — GSAP handles the measurement automatically.</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-icon">◆</span>
            <span class="at-title">Why not use CSS max-height trick?</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>The CSS <code>max-height</code> trick requires setting a large arbitrary maximum (e.g., <code>max-height: 1000px</code>), which causes easing to feel wrong — the element accelerates until it hits the actual content height, then stops abruptly.</p>
              <p>GSAP measures the real target height and creates a precise, spring-eased animation with no easing artifacts.</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-icon">◆</span>
            <span class="at-title">Accessibility considerations</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>Always set <code>aria-expanded</code> on the trigger button and toggle it on state change. The panel body should have a matching <code>aria-hidden</code> attribute. Screen readers need these attributes to announce the expanded/collapsed state correctly.</p>
              <p>For <code>prefers-reduced-motion</code>, skip the tween and immediately set the final state using <code>gsap.set()</code>.</p>
            </div>
          </div>
        </div>
      </div>
    </section>

    <!-- Variant 2: Multi-open -->
    <section class="demo-section">
      <div class="demo-label">
        <span class="variant-tag">Variant B</span>
        <h2>Multi-open — independent panels</h2>
      </div>
      <div class="accordion accordion--open" id="acc-multi" data-mode="multi">
        <div class="acc-item acc-item--open">
          <button class="acc-trigger" aria-expanded="true">
            <span class="at-num">01</span>
            <span class="at-title">Research & Discovery</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner acc-inner--timeline">
              <div class="tl-item">
                <span class="tl-week">Week 1–2</span>
                <span class="tl-task">Stakeholder interviews + competitive analysis</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 3</span>
                <span class="tl-task">User research sessions + affinity mapping</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 4</span>
                <span class="tl-task">Synthesis + problem statement</span>
              </div>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-num">02</span>
            <span class="at-title">Design & Prototyping</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner acc-inner--timeline">
              <div class="tl-item">
                <span class="tl-week">Week 5–6</span>
                <span class="tl-task">Wireframes + IA architecture</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 7</span>
                <span class="tl-task">High-fidelity mockups + design system</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 8</span>
                <span class="tl-task">Interactive prototype</span>
              </div>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-num">03</span>
            <span class="at-title">Development & Launch</span>
            <span class="at-arrow">↓</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner acc-inner--timeline">
              <div class="tl-item">
                <span class="tl-week">Week 9–12</span>
                <span class="tl-task">Frontend development + integration</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 13</span>
                <span class="tl-task">QA + performance testing</span>
              </div>
              <div class="tl-item">
                <span class="tl-week">Week 14</span>
                <span class="tl-task">Launch + monitoring</span>
              </div>
            </div>
          </div>
        </div>
      </div>
    </section>

    <!-- Variant 3: Minimal / Borderless -->
    <section class="demo-section">
      <div class="demo-label">
        <span class="variant-tag">Variant C</span>
        <h2>Minimal line style</h2>
      </div>
      <div class="accordion accordion--minimal" id="acc-minimal" data-mode="exclusive">
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-title">Typography</span>
            <span class="at-arrow">+</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>Variable fonts, optical sizing, fluid type scales using <code>clamp()</code>, and responsive line-height that adapts to reading distance on different devices.</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-title">Color Systems</span>
            <span class="at-arrow">+</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>Semantic color tokens, dark/light mode with CSS custom properties, contrast checking with WCAG 2.1 AAA, and perceptual color spaces (oklch).</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-title">Motion Design</span>
            <span class="at-arrow">+</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>Timing functions based on physics (spring, expo, elastic), duration scaling by distance, and choreographed stagger patterns that feel natural.</p>
            </div>
          </div>
        </div>
        <div class="acc-item">
          <button class="acc-trigger" aria-expanded="false">
            <span class="at-title">Spacing & Layout</span>
            <span class="at-arrow">+</span>
          </button>
          <div class="acc-body">
            <div class="acc-inner">
              <p>8-point grid systems, intrinsic web design with CSS Grid subgrid, aspect-ratio locking, and content-driven breakpoints rather than device-based.</p>
            </div>
          </div>
        </div>
      </div>
    </section>

  </div>

  <script type="module" src="script.js"></script>
</body>
</html>

GSAP Accordion

Three accordion variants (exclusive, multi-open, minimal) using GSAP height:‘auto’ animation. Demonstrates smooth open/close without CSS max-height artifacts, arrow rotation spring ease, and aria attributes.

Source

Repository: libs-genclaude
Original demo id: 50-gsap-accordion

程式碼

GSAP Accordion

Source

Notes