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28 Rotating word swapper

Motion · Type in motion
Rotating word swapper

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Prompt

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Rotating word swapper — Rotating word swapper

Build an effect where a single word inside a sentence rolls vertically to the next as the page scrolls. The outer section is 300vh tall and holds a 100vh box with position: sticky; top: 0 that keeps one large sentence (40–72px, line-height 1.3) centred on screen. Put the changing word in a frame 1.3em tall with overflow: hidden, and stack four words vertically inside it. Compute the progress p (0 to 1) as p=0 when the section's top reaches the top of the screen and p=1 when its bottom reaches the bottom, then move the word column up by k = floor(p × 4) lines (3 at most) with translateY(k × -1.3em). Animate that move with a 0.7-second transform transition, and leave the rest of the sentence still. Implement it with plain CSS and JavaScript only, with no library.

Do not drop:
- Keep the frame and each word exactly one line tall (1.3em); any mismatch lets the neighbouring words show
- Size the frame to the widest of the four words and keep it fixed; resizing it per word shifts the text after it
- Choose the word from scroll progress p, never from a timer
- Under prefers-reduced-motion, release the pin and show the finished sentence with the fourth word, static

A working example (one self-contained HTML file): https://design-vault.pages.dev/designs/motion-word-swapper/demo.html

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demo.html

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/designs/motion-word-swapper/demo.html — One self-contained HTML file. CSS and plain JavaScript only; it fetches nothing.

Show contents 
<!doctype html>
<html lang="ja">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>28 ワードスワッパー — Rotating word swapper</title>
<style>
/* dv-motion-base:start */
:root {
  --ground: #FFFFFF;
  --surface: #F3F5F8;
  --ink: #14181F;
  --muted: #5A6472;
  --accent: #1F5FA8;
  --rule: #D8DDE4;
  --accent-soft: color-mix(in srgb, var(--accent) 12%, var(--ground));
  --accent-mid: color-mix(in srgb, var(--accent) 45%, var(--ground));
  --shade: color-mix(in srgb, var(--ink) 14%, transparent);

  --font: "Zen Kaku Gothic New", "Hiragino Sans", "Noto Sans JP", "Yu Gothic", system-ui, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;

  --t-label: 13px;
  --t-body: 16px;
  --t-lead: 20px;
  --t-h2: 32px;
  --t-h1: clamp(40px, 7vw, 72px);

  --s1: 4px;
  --s2: 8px;
  --s3: 16px;
  --s4: 24px;
  --s5: 40px;
  --s6: 64px;
  --s7: 104px;

  --radius: 12px;
  --ease: cubic-bezier(.2, .7, .2, 1);
  --dur: .7s;
  --measure: 1080px;
}
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--ground);
  color: var(--ink);
  font-family: var(--font);
  font-size: var(--t-body);
  line-height: 1.7;
  font-feature-settings: "palt";
  overflow-x: hidden;
}
h1, h2, h3, p, ul, ol, figure { margin: 0; padding: 0; }
ul, ol { list-style: none; }
.dv-wrap { width: min(100% - 2 * var(--s4), var(--measure)); margin-inline: auto; }
.dv-label {
  min-height: 72vh;
  display: grid;
  align-content: center;
  gap: var(--s3);
  padding-block: var(--s6);
  border-bottom: 1px solid var(--rule);
}
.dv-num { font-family: var(--mono); font-size: var(--t-lead); font-weight: 700; color: var(--accent); letter-spacing: .04em; }
.dv-name { font-size: var(--t-h1); font-weight: 700; line-height: 1.15; letter-spacing: .01em; }
.dv-ai { font-family: var(--mono); font-size: var(--t-lead); color: var(--muted); }
.dv-desc { font-size: var(--t-lead); color: var(--ink); }
.dv-hint { font-size: var(--t-label); color: var(--muted); letter-spacing: .12em; margin-top: var(--s4); }
.dv-stage { padding-block: var(--s7); }
.dv-h2 { font-size: var(--t-h2); font-weight: 700; line-height: 1.3; }
.dv-lead { font-size: var(--t-lead); color: var(--muted); }
.dv-eyebrow { font-family: var(--mono); font-size: var(--t-label); color: var(--accent); letter-spacing: .12em; text-transform: uppercase; }
.dv-card { background: var(--surface); border: 1px solid var(--rule); border-radius: var(--radius); padding: var(--s4); }
.dv-ph {
  border-radius: var(--radius);
  background: linear-gradient(135deg, var(--accent-soft), var(--accent-mid) 60%, var(--accent));
  aspect-ratio: 16 / 9;
}
.dv-ph--alt { background: linear-gradient(200deg, var(--surface), var(--accent-soft) 55%, var(--accent-mid)); }
.dv-ph--ink { background: linear-gradient(160deg, var(--ink), color-mix(in srgb, var(--ink) 55%, var(--accent))); }
.dv-end {
  min-height: 60vh;
  display: grid;
  place-items: center;
  border-top: 1px solid var(--rule);
  color: var(--muted);
  font-family: var(--mono);
  font-size: var(--t-label);
  letter-spacing: .12em;
}
/* dv-motion-base:end */

/* ---- この演出だけの CSS。色は var(--…) か color-mix() のみ ---- */
.swap-zone { height: 300vh; }
.swap-box {
  position: sticky;
  top: 0;
  height: 100vh;
  display: grid;
  align-content: center;
  gap: var(--s4);
}
.swap-line {
  --lh: 1.3;
  font-size: var(--t-h1);
  font-weight: 700;
  line-height: var(--lh);
  letter-spacing: .01em;
}
.swap-part { display: inline-block; white-space: nowrap; }
/* 語の枠。高さを 1 行ぶんに揃え、はみ出した前後の語を切る */
.swap-win {
  display: inline-grid;
  height: calc(var(--lh) * 1em);
  overflow: hidden;
  vertical-align: bottom;
  margin-inline: .08em;
  padding-inline: .14em;
  border-radius: var(--radius);
  background: var(--accent-soft);
  color: var(--accent);
}
.swap-roll {
  display: grid;
  transform: translateY(calc(var(--k, 0) * -1 * var(--lh) * 1em));
  transition: transform var(--dur) var(--ease);
}
.swap-word { height: calc(var(--lh) * 1em); white-space: nowrap; }
.swap-foot { display: grid; grid-template-columns: auto minmax(0, 1fr); align-items: center; gap: var(--s3); }
.swap-count { font-family: var(--mono); font-size: var(--t-label); color: var(--muted); letter-spacing: .12em; font-variant-numeric: tabular-nums; }
.swap-ticks { display: grid; grid-template-columns: repeat(4, 1fr); gap: var(--s2); }
.swap-tick {
  height: 4px;
  border-radius: 2px;
  background: var(--rule);
  transition: background-color var(--dur) var(--ease);
}
.swap-tick.is-on { background: var(--accent); }
html:not(.js) .swap-foot { display: none; }

@media (prefers-reduced-motion: reduce) {
  .swap-zone { height: auto; }
  .swap-box { position: static; height: auto; padding-block: var(--s7); }
  .swap-roll, .swap-tick { transition: none; }
}
</style>
</head>
<body data-motion-number="28">
<header class="dv-label">
  <div class="dv-wrap">
    <p class="dv-num">28</p>
    <h1 class="dv-name">ワードスワッパー</h1>
    <p class="dv-ai">Rotating word swapper</p>
    <p class="dv-desc">一語が縦に入れ替わっていく</p>
    <p class="dv-hint">SCROLL ↓</p>
  </div>
</header>

<main class="dv-stage">
  <div class="dv-wrap">
    <section class="swap-zone" data-progress="pin">
      <div class="swap-box">
        <p class="dv-eyebrow">Word swapper</p>
        <h2 class="swap-line">
          <span class="swap-part">毎日の</span><span class="swap-part"><span class="swap-win"><span class="swap-roll"><span class="swap-word">資料</span><span class="swap-word">提案</span><span class="swap-word">報告</span><span class="swap-word">企画</span></span></span>づくりを、</span><span class="swap-part">もっと速く。</span>
        </h2>
        <p class="dv-lead">本文のダミーです。文は動かず、枠の中の一語だけが入れ替わります。</p>
        <div class="swap-foot">
          <p class="swap-count" aria-hidden="true">01 / 04</p>
          <div class="swap-ticks" aria-hidden="true">
            <span class="swap-tick"></span>
            <span class="swap-tick"></span>
            <span class="swap-tick"></span>
            <span class="swap-tick"></span>
          </div>
        </div>
      </div>
    </section>
  </div>
</main>

<footer class="dv-end">END — 28 ワードスワッパー</footer>

<script>
/* dv-motion-helpers:start */
const dvReduce = matchMedia('(prefers-reduced-motion: reduce)').matches;
document.documentElement.classList.add('js');

/**
 * 画面に入った要素へ .is-in を付ける。
 * data-reveal="repeat" の要素は画面を出たら外す（何度でも再生）。
 */
function dvReveal(selector = '[data-reveal]', { threshold = 0.2, rootMargin = '0px 0px -8% 0px' } = {}) {
  const els = [...document.querySelectorAll(selector)];
  if (dvReduce || !('IntersectionObserver' in window)) {
    els.forEach((el) => el.classList.add('is-in'));
    return;
  }
  const io = new IntersectionObserver((entries) => {
    for (const e of entries) {
      if (e.isIntersecting) {
        e.target.classList.add('is-in');
        if (e.target.dataset.reveal !== 'repeat') io.unobserve(e.target);
      } else if (e.target.dataset.reveal === 'repeat') {
        e.target.classList.remove('is-in');
      }
    }
  }, { threshold, rootMargin });
  els.forEach((el) => io.observe(el));
}

/**
 * スクロール量を 0〜1 にして、各 [data-progress] 要素の CSS 変数 --p に書く。
 *   data-progress="through" : 要素の上端が画面の下端に来たとき 0、下端が画面の上端を抜けたとき 1
 *   data-progress="pin"     : 要素の上端が画面の上端に来たとき 0、下端が画面の下端に来たとき 1
 *                             （中に position: sticky の箱を持つ、背の高い区画用）
 *   data-progress="page"    : ページ全体のスクロール量
 * onUpdate(el, p) を渡すと、値が変わるたびに呼ばれる。
 */
function dvProgress(onUpdate) {
  const els = [...document.querySelectorAll('[data-progress]')];
  const clamp = (n) => Math.min(1, Math.max(0, n));
  let queued = false;
  const measure = () => {
    queued = false;
    const vh = window.innerHeight;
    for (const el of els) {
      const r = el.getBoundingClientRect();
      let p;
      if (el.dataset.progress === 'pin') p = r.height > vh ? -r.top / (r.height - vh) : 0;
      else if (el.dataset.progress === 'page') {
        const max = document.documentElement.scrollHeight - vh;
        p = max > 0 ? window.scrollY / max : 0;
      } else p = (vh - r.top) / (vh + r.height);
      p = clamp(p);
      el.style.setProperty('--p', p.toFixed(4));
      if (onUpdate) onUpdate(el, p);
    }
  };
  const request = () => {
    if (!queued) { queued = true; requestAnimationFrame(measure); }
  };
  addEventListener('scroll', request, { passive: true });
  addEventListener('resize', request);
  measure();
}
/* dv-motion-helpers:end */

/* ---- この演出だけの JS ---- */
dvProgress((el, p) => {
  // 進み具合を 4 等分し、その番号ぶんだけ語の列を 1 行ずつ上へ送る
  const k = dvReduce ? 3 : Math.min(3, Math.floor(p * 4));
  el.style.setProperty('--k', k);
  el.querySelectorAll('.swap-word').forEach((w, i) => w.setAttribute('aria-hidden', i === k ? 'false' : 'true'));
  el.querySelectorAll('.swap-tick').forEach((t, i) => t.classList.toggle('is-on', i <= k));
  el.querySelector('.swap-count').textContent = '0' + (k + 1) + ' / 04';
});
</script>
</body>
</html>

/ai/assets/motion-word-swapper.json