01Bar Chart Loading Skeleton Whose Delay Is Computed Per Bar

<main class="stage">
<div class="cb is-demo" id="cb">
  <div class="cb__chart" id="cbChart" role="img" aria-label="Monthly visitors bar chart" aria-busy="true">
    <div class="cb__col" data-i="0"><div class="cb__bar" id="cbBar0"></div></div>
    <div class="cb__col" data-i="1"><div class="cb__bar" id="cbBar1"></div></div>
    <div class="cb__col" data-i="2"><div class="cb__bar" id="cbBar2"></div></div>
    <div class="cb__col" data-i="3"><div class="cb__bar" id="cbBar3"></div></div>
    <div class="cb__col" data-i="4"><div class="cb__bar" id="cbBar4"></div></div>
    <div class="cb__col" data-i="5"><div class="cb__bar" id="cbBar5"></div></div>
  </div>
  <button type="button" class="cb__reload" id="cbReload">Reload</button>
</div>
</main>

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

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

@include stage($stage-ink);

.cb { width: min(300px, 88vw); }
.cb__chart {
  display: flex; align-items: flex-end; justify-content: space-between;
  gap: $sp-2; height: 150px; padding: 0 $sp-1;
  border-bottom: 2px solid rgba($subject-cream, .18);
}
.cb__col { flex: 1 1 0; height: 100%; display: flex; align-items: flex-end; }
.cb__bar {
  width: 100%; height: 100%; border-radius: $r-xs $r-xs 0 0;
  background: $color; transform-origin: bottom; // 시작 변(바닥)에서 자란다 — 채움 막대 예외(규칙 8)
  transform: scaleY(.16); opacity: .32;
  animation: cbReveal $duration var(--phase, 0ms) $easing infinite;
}
.cb__reload {
  display: block; margin: $sp-4 auto 0; appearance: none; border: none; cursor: pointer;
  background: rgba($subject-cream, .12); color: $subject-cream; font-weight: 700; font-size: 13px;
  padding: $sp-2 $sp-4; border-radius: $r-pill;
}
.cb__reload:focus-visible { outline: 2px solid $subject-cream; outline-offset: 2px; }

@keyframes cbReveal {
  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; }
}

@media (max-width: 340px) {
  .cb { width: min(250px, 84vw); }
  .cb__chart { height: 120px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용: 자동 루프를 끄고 마지막 실제 값 상태로 고정한다
  .cb__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.cb {
  width: min(300px, 88vw);
}

.cb__chart {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 8px;
  height: 150px;
  padding: 0 4px;
  border-bottom: 2px solid rgba(255, 247, 230, 0.18);
}

.cb__col {
  flex: 1 1 0;
  height: 100%;
  display: flex;
  align-items: flex-end;
}

.cb__bar {
  width: 100%;
  height: 100%;
  border-radius: 4px 4px 0 0;
  background: #2f6df6;
  transform-origin: bottom;
  transform: scaleY(0.16);
  opacity: 0.32;
  animation: cbReveal 2s var(--phase, 0ms) cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.cb__reload {
  display: block;
  margin: 16px auto 0;
  appearance: none;
  border: none;
  cursor: pointer;
  background: rgba(255, 247, 230, 0.12);
  color: #fff7e6;
  font-weight: 700;
  font-size: 13px;
  padding: 8px 16px;
  border-radius: 999px;
}

.cb__reload:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 2px;
}

@keyframes cbReveal {
  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;
  }
}
@media (max-width: 340px) {
  .cb {
    width: min(250px, 84vw);
  }
  .cb__chart {
    height: 120px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .cb__bar {
    animation: none;
    transform: scaleY(var(--real, 0.6));
    opacity: 1;
  }
}

(function () {
  var VALUES = [38, 82, 55, 96, 29, 68];
  var STAGGER_MS = 70;
  var SKELETON_SCALE = 0.16;
  var root = document.getElementById('cb');
  var chart = document.getElementById('cbChart');
  var reload = document.getElementById('cbReload');
  var bars = VALUES.map(function (v, i) { return document.getElementById('cbBar' + i); });

  // 계산 겹: 막대 등장 지연을 열 번호(i)로 계산한다 — 열이 오른쪽일수록 늦게 실제 높이로 펴진다
  function barDelay(i) { return i * STAGGER_MS; }

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

  function paintNow(i, value) {
    bars[i].style.transform = 'scaleY(' + (value / 100) + ')';
    bars[i].style.opacity = '1';
  }
  function skeletonNow(i) {
    bars[i].style.transform = 'scaleY(' + SKELETON_SCALE + ')';
    bars[i].style.opacity = '.32';
  }

  function human() {
    root.classList.remove('is-demo');
    bars.forEach(function (bar, i) { skeletonNow(i); });
    chart.setAttribute('aria-busy', 'true');
    bars.forEach(function (bar, i) {
      window.setTimeout(function () { paintNow(i, VALUES[i]); }, 260 + barDelay(i));
    });
    window.setTimeout(function () { chart.setAttribute('aria-busy', 'false'); }, 260 + barDelay(VALUES.length - 1) + 200);
  }

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

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

const VALUES = [38, 82, 55, 96, 29, 68];
const STAGGER_MS = 70;
const SKELETON_SCALE = 0.16;

export default function ChartLoadingBarHeightStagger() {
  const rootRef = useRef<HTMLDivElement>(null);
  const chartRef = useRef<HTMLDivElement>(null);
  const reloadRef = useRef<HTMLButtonElement>(null);
  const barRefs = useRef<HTMLDivElement[]>([]);

  useEffect(() => {
    const root = rootRef.current;
    const chart = chartRef.current;
    const reload = reloadRef.current;
    if (!root || !chart || !reload) return undefined;
    const bars = barRefs.current!;
    if (!bars || bars.length !== VALUES.length) return undefined;

    // 계산 겹: 막대 등장 지연을 열 번호(i)로 계산한다 — 열이 오른쪽일수록 늦게 실제 높이로 펴진다
    function barDelay(i: number) { return i * STAGGER_MS; }

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

    function paintNow(i: number, value: number) {
      bars[i].style.transform = 'scaleY(' + (value / 100) + ')';
      bars[i].style.opacity = '1';
    }
    function skeletonNow(i: number) {
      bars[i].style.transform = 'scaleY(' + SKELETON_SCALE + ')';
      bars[i].style.opacity = '.32';
    }

    const timers: number[] = [];
    function human() {
      root!.classList.remove(styles['is-demo']);
      bars.forEach((_bar, i) => skeletonNow(i));
      chart!.setAttribute('aria-busy', 'true');
      bars.forEach((_bar, i) => {
        timers.push(window.setTimeout(() => paintNow(i, VALUES[i]), 260 + barDelay(i)));
      });
      timers.push(window.setTimeout(() => chart!.setAttribute('aria-busy', 'false'), 260 + barDelay(VALUES.length - 1) + 200));
    }

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

    reload.addEventListener('click', onClick);
    reload.addEventListener('keydown', onKey);
    return () => {
      reload.removeEventListener('click', onClick);
      reload.removeEventListener('keydown', onKey);
      timers.forEach((id) => window.clearTimeout(id));
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.cb + ' ' + styles['is-demo']} ref={rootRef}>
        <div className={styles.cbChart} ref={chartRef} role="img" aria-label="월별 방문자 막대 그래프" aria-busy="true">
          {VALUES.map((_value, i) => (
            <div className={styles.cbCol} data-i={i} key={i}>
              <div
                className={styles.cbBar}
                ref={(el: HTMLDivElement | null) => { if (el) barRefs.current![i] = el; }}
              />
            </div>
          ))}
        </div>
        <button type="button" className={styles.cbReload} ref={reloadRef}>다시 불러오기</button>
      </div>
    </main>
  );
}