09Chart Loading That Skips Computation and Swaps Instantly Under Reduced Motion

<main class="stage">
<div class="cr is-demo" id="cr">
  <p class="cr__status" id="crStatus" aria-live="polite">Setting: Normal animation</p>
  <div class="cr__row">
    <div class="cr__col">
      <span class="cr__label">Normal transition</span>
      <div class="cr__chart" role="img" aria-label="Normal transition bar chart" aria-busy="true">
        <div class="cr__bar cr__bar--normal" id="crN0"></div>
        <div class="cr__bar cr__bar--normal" id="crN1"></div>
        <div class="cr__bar cr__bar--normal" id="crN2"></div>
        <div class="cr__bar cr__bar--normal" id="crN3"></div>
      </div>
    </div>
    <div class="cr__col">
      <span class="cr__label">Reduced motion (reference)</span>
      <div class="cr__chart" role="img" aria-label="Reduced motion bar chart" aria-busy="true">
        <div class="cr__bar cr__bar--reduced" id="crR0"></div>
        <div class="cr__bar cr__bar--reduced" id="crR1"></div>
        <div class="cr__bar cr__bar--reduced" id="crR2"></div>
        <div class="cr__bar cr__bar--reduced" id="crR3"></div>
      </div>
    </div>
  </div>
  <button type="button" class="cr__toggle" id="crToggle" aria-pressed="false">Preview accessibility mode</button>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 변수 3개
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-paper);

.cr { width: min(300px, 88vw); text-align: center; }
.cr__status { margin: 0 0 $sp-2; font-size: 11px; font-weight: 700; color: rgba($subject-ink, .6); }
.cr__row { display: flex; gap: $sp-3; }
.cr__col { flex: 1 1 0; min-width: 0; }
.cr__label { display: block; margin-bottom: $sp-1; font-size: 11px; font-weight: 700; color: rgba($subject-ink, .68); }
.cr__chart {
  display: flex; align-items: flex-end; justify-content: space-between; gap: $sp-1;
  height: 84px; padding: 0 $sp-1; border-bottom: 2px solid rgba($subject-ink, .16);
}
.cr__bar { width: 100%; height: 100%; border-radius: $r-xs $r-xs 0 0; transform-origin: bottom; transform: scaleY(.16); opacity: .32; }
.cr__bar--normal { background: $color; animation: crRevealSmooth $duration var(--phase, 0ms) $easing infinite; }
.cr__bar--reduced { background: $chart-3; animation: crRevealInstant $duration $easing infinite; }

.cr--force-instant .cr__bar--normal { animation-name: crRevealInstant; animation-delay: 0ms; }

.cr__toggle {
  display: block; margin: $sp-3 auto 0; appearance: none; border: none; cursor: pointer;
  background: $subject-ink; color: $subject-cream; font-weight: 700; font-size: 12px;
  padding: $sp-1 $sp-3; border-radius: $r-pill;
}
.cr__toggle:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }
.cr__toggle[aria-pressed="true"] { background: $subject-blue; }

@keyframes crRevealSmooth {
  0%   { transform: scaleY(.16); opacity: .32; }
  14%  { transform: scaleY(.16); opacity: .32; }
  46%  { transform: scaleY(var(--real, .6)); opacity: 1; }
  84%  { transform: scaleY(var(--real, .6)); opacity: 1; }
  100% { transform: scaleY(.16); opacity: .32; }
}

// 줄인 모션 참고 열: steps(1,end) 로 중간 프레임 없이 한 번에 바뀐다(진짜 즉시 전환)
@keyframes crRevealInstant {
  0%   { transform: scaleY(.16); opacity: .32; }
  45%  { transform: scaleY(.16); opacity: .32; }
  46%  { transform: scaleY(var(--real, .6)); opacity: 1; }
  84%  { transform: scaleY(var(--real, .6)); opacity: 1; }
  85%  { transform: scaleY(.16); opacity: .32; }
  100% { transform: scaleY(.16); opacity: .32; }
}
.cr__bar--reduced, .cr--force-instant .cr__bar--normal {
  animation-timing-function: steps(1, end);
}

@media (max-width: 340px) {
  .cr { width: min(250px, 86vw); }
  .cr__chart { height: 68px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용: 두 열 다 애니메이션을 멈추고 완성된 높이만 보인다
  .cr__bar { animation: none; transform: scaleY(var(--real, .6)); opacity: 1; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.cr {
  width: min(300px, 88vw);
  text-align: center;
}

.cr__status {
  margin: 0 0 8px;
  font-size: 11px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.6);
}

.cr__row {
  display: flex;
  gap: 12px;
}

.cr__col {
  flex: 1 1 0;
  min-width: 0;
}

.cr__label {
  display: block;
  margin-bottom: 4px;
  font-size: 11px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.68);
}

.cr__chart {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 4px;
  height: 84px;
  padding: 0 4px;
  border-bottom: 2px solid rgba(23, 20, 26, 0.16);
}

.cr__bar {
  width: 100%;
  height: 100%;
  border-radius: 4px 4px 0 0;
  transform-origin: bottom;
  transform: scaleY(0.16);
  opacity: 0.32;
}

.cr__bar--normal {
  background: #2f6df6;
  animation: crRevealSmooth 2s var(--phase, 0ms) cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.cr__bar--reduced {
  background: #2b9d74;
  animation: crRevealInstant 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.cr--force-instant .cr__bar--normal {
  animation-name: crRevealInstant;
  animation-delay: 0ms;
}

.cr__toggle {
  display: block;
  margin: 12px auto 0;
  appearance: none;
  border: none;
  cursor: pointer;
  background: #17141a;
  color: #fff7e6;
  font-weight: 700;
  font-size: 12px;
  padding: 4px 12px;
  border-radius: 999px;
}

.cr__toggle:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.cr__toggle[aria-pressed=true] {
  background: #2f6df6;
}

@keyframes crRevealSmooth {
  0% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
  14% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
  46% {
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
  84% {
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
  100% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
}
@keyframes crRevealInstant {
  0% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
  45% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
  46% {
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
  84% {
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
  85% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
  100% {
    transform: scaleY(0.16);
    opacity: 0.32;
  }
}
.cr__bar--reduced, .cr--force-instant .cr__bar--normal {
  animation-timing-function: steps(1, end);
}

@media (max-width: 340px) {
  .cr {
    width: min(250px, 86vw);
  }
  .cr__chart {
    height: 68px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .cr__bar {
    animation: none;
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
}

(function () {
  var VALUES = [64, 88, 42, 76];
  var STAGGER_MS = 80;
  var root = document.getElementById('cr');
  var status = document.getElementById('crStatus');
  var toggle = document.getElementById('crToggle');
  var normalBars = [0, 1, 2, 3].map(function (i) { return document.getElementById('crN' + i); });
  var reducedBars = [0, 1, 2, 3].map(function (i) { return document.getElementById('crR' + i); });

  // 계산 겹: 같은 공식에 감쇠 계수(reduced)를 곱한다 — 줄인 모션이면 지연이 전부 0 으로 접힌다
  function barDelay(i, reduced) { return reduced ? 0 : i * STAGGER_MS; }

  normalBars.forEach(function (bar, i) {
    bar.style.setProperty('--real', String(VALUES[i] / 100));
    bar.style.setProperty('--phase', barDelay(i, false) + 'ms');
  });
  reducedBars.forEach(function (bar, i) {
    bar.style.setProperty('--real', String(VALUES[i] / 100));
    bar.style.setProperty('--phase', barDelay(i, true) + 'ms');
  });

  // 실사용 경로: 브라우저의 실제 설정을 읽는다(시뮬레이션이 아니다)
  var mql = window.matchMedia('(prefers-reduced-motion: reduce)');

  function updateStatus() {
    var real = mql.matches;
    var sim = root.classList.contains('cr--reduced-sim');
    var forced = real || sim;
    root.classList.toggle('cr--force-instant', forced);
    if (real) {
      status.textContent = 'Setting: Your browser has reduced motion turned on';
    } else if (sim) {
      status.textContent = 'Setting: Previewing accessibility mode (simulated)';
    } else {
      status.textContent = 'Setting: Normal animation';
    }
  }

  if (mql.addEventListener) {
    mql.addEventListener('change', updateStatus);
  } else if (mql.addListener) {
    mql.addListener(updateStatus);
  }
  updateStatus();

  // 데모용 시뮬레이션 토글: 실제 OS 설정을 바꾸지 않고도 차이를 미리 보여준다
  function human() {
    root.classList.remove('is-demo');
    var next = !root.classList.contains('cr--reduced-sim');
    root.classList.toggle('cr--reduced-sim', next);
    toggle.setAttribute('aria-pressed', String(next));
    updateStatus();
  }

  toggle.addEventListener('click', human);
  toggle.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); human(); }
  });
}());

import { useEffect, useRef } from 'react';
import styles from './ChartLoadingReducedMotionInstantSwap.module.scss';

const VALUES = [64, 88, 42, 76];
const STAGGER_MS = 80;
// 시뮬레이션 상태만 표시하는 내부 플래그 클래스 — CSS 규칙이 없어 스타일 모듈 맵을 거치지 않는다(vanilla 와 동일)
const REDUCED_SIM_CLASS = 'crReducedSim';

export default function ChartLoadingReducedMotionInstantSwap() {
  const rootRef = useRef<HTMLDivElement>(null);
  const statusRef = useRef<HTMLParagraphElement>(null);
  const toggleRef = useRef<HTMLButtonElement>(null);
  const normalRefs = useRef<HTMLDivElement[]>([]);
  const reducedRefs = useRef<HTMLDivElement[]>([]);

  useEffect(() => {
    const root = rootRef.current;
    const status = statusRef.current;
    const toggle = toggleRef.current;
    if (!root || !status || !toggle) return undefined;
    const normalBars = normalRefs.current!;
    const reducedBars = reducedRefs.current!;
    if (!normalBars || !reducedBars) return undefined;

    // 계산 겹: 같은 공식에 감쇠 계수(reduced)를 곱한다 — 줄인 모션이면 지연이 전부 0 으로 접힌다
    function barDelay(i: number, reduced: boolean) { return reduced ? 0 : i * STAGGER_MS; }

    normalBars.forEach((bar, i) => {
      bar.style.setProperty('--real', String(VALUES[i] / 100));
      bar.style.setProperty('--phase', barDelay(i, false) + 'ms');
    });
    reducedBars.forEach((bar, i) => {
      bar.style.setProperty('--real', String(VALUES[i] / 100));
      bar.style.setProperty('--phase', barDelay(i, true) + 'ms');
    });

    // 실사용 경로: 브라우저의 실제 설정을 읽는다(시뮬레이션이 아니다)
    const mql = window.matchMedia('(prefers-reduced-motion: reduce)');

    function updateStatus() {
      const real = mql.matches;
      const sim = root!.classList.contains(REDUCED_SIM_CLASS);
      const forced = real || sim;
      root!.classList.toggle(styles.crForceInstant, forced);
      if (real) {
        status!.textContent = '설정: 브라우저의 애니메이션 줄이기가 켜져 있습니다';
      } else if (sim) {
        status!.textContent = '설정: 접근성 모드 미리보기 중(시뮬레이션)';
      } else {
        status!.textContent = '설정: 애니메이션 보통';
      }
    }

    type LegacyMql = MediaQueryList & { addListener?: (cb: () => void) => void; removeListener?: (cb: () => void) => void };
    const legacyMql = mql as LegacyMql;
    if (mql.addEventListener) {
      mql.addEventListener('change', updateStatus);
    } else if (legacyMql.addListener) {
      legacyMql.addListener(updateStatus);
    }
    updateStatus();

    // 데모용 시뮬레이션 토글: 실제 OS 설정을 바꾸지 않고도 차이를 미리 보여준다
    function human() {
      root!.classList.remove(styles['is-demo']);
      const next = !root!.classList.contains(REDUCED_SIM_CLASS);
      root!.classList.toggle(REDUCED_SIM_CLASS, next);
      toggle!.setAttribute('aria-pressed', String(next));
      updateStatus();
    }

    function onClick() { human(); }
    function onKey(e: KeyboardEvent) { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); human(); } }
    toggle.addEventListener('click', onClick);
    toggle.addEventListener('keydown', onKey);

    return () => {
      toggle.removeEventListener('click', onClick);
      toggle.removeEventListener('keydown', onKey);
      if (mql.removeEventListener) {
        mql.removeEventListener('change', updateStatus);
      } else if (legacyMql.removeListener) {
        legacyMql.removeListener(updateStatus);
      }
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.cr + ' ' + styles['is-demo']} ref={rootRef}>
        <p className={styles.crStatus} ref={statusRef} aria-live="polite">설정: 애니메이션 보통</p>
        <div className={styles.crRow}>
          <div className={styles.crCol}>
            <span className={styles.crLabel}>일반 전환</span>
            <div className={styles.crChart} role="img" aria-label="일반 전환 막대 그래프" aria-busy="true">
              {VALUES.map((_v, i) => (
                <div
                  key={i}
                  className={styles.crBar + ' ' + styles.crBarNormal}
                  ref={(el: HTMLDivElement | null) => { if (el) normalRefs.current![i] = el; }}
                />
              ))}
            </div>
          </div>
          <div className={styles.crCol}>
            <span className={styles.crLabel}>줄인 모션(참고)</span>
            <div className={styles.crChart} role="img" aria-label="줄인 모션 막대 그래프" aria-busy="true">
              {VALUES.map((_v, i) => (
                <div
                  key={i}
                  className={styles.crBar + ' ' + styles.crBarReduced}
                  ref={(el: HTMLDivElement | null) => { if (el) reducedRefs.current![i] = el; }}
                />
              ))}
            </div>
          </div>
        </div>
        <button type="button" className={styles.crToggle} ref={toggleRef} aria-pressed="false">접근성 모드로 미리보기</button>
      </div>
    </main>
  );
}