GSAP Accordion

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":"/vendor/gsap/index.js","gsap/ScrollTrigger":"/vendor/gsap/ScrollTrigger.js","gsap/SplitText":"/vendor/gsap/SplitText.js","gsap/Flip":"/vendor/gsap/Flip.js","gsap/ScrambleTextPlugin":"/vendor/gsap/ScrambleTextPlugin.js","gsap/TextPlugin":"/vendor/gsap/TextPlugin.js","gsap/all":"/vendor/gsap/all.js","gsap/":"/vendor/gsap/","lenis":"/vendor/lenis/dist/lenis.mjs","three":"/vendor/three/build/three.module.js","three/addons/":"/vendor/three/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>

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</body>
</html>