09Bar response — a button where several bars' height values jump by differing amounts on each click before settling

<main class="stage">
<div class="ctavum is-demo" id="ctavum">
  <div class="ctavum__panel">
    <button class="ctavum__btn" id="ctavumBtn" type="button">
      <span class="ctavum__bars" id="ctavumBars"></span>
      <span class="ctavum__label">Turn on notification sound</span>
    </button>
    <span class="ctavum__hint">Each click makes the bars jump then settle</span>
  </div>
</div>
</main>

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

// 계산 겹(피크-감쇠 곡선)은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-ink);

.stage { position: relative; }

.ctavum__panel {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
  padding: $sp-5;
  border-radius: $r-card;
  background: $tick-panel;
}

.ctavum__btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
  border: 0;
  border-radius: $r-control;
  background: $subject-ink;
  padding: $sp-4 $sp-5;
  cursor: pointer;
}

.ctavum__bars {
  display: flex;
  align-items: flex-end;
  gap: 4px;
  height: 40px;
}

.ctavum__bar {
  width: 6px;
  height: 14%;
  border-radius: $r-xs;
  background: $tick-up;
}

.ctavum__bar:nth-child(4),
.ctavum__bar:nth-child(5) {
  background: $tick-down;
}

.ctavum__label {
  color: $subject-cream;
  font-family: inherit;
  font-weight: 700;
  font-size: 13px;
}

.ctavum__hint {
  color: $tick-mute;
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .ctavum__panel { padding: $sp-4; gap: $sp-3; }
  .ctavum__btn { padding: $sp-3 $sp-4; }
  .ctavum__bars { height: 34px; }
}

@media (prefers-reduced-motion: reduce) {
  .ctavum__bar { transition: none !important; }
}

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);
}

.stage {
  position: relative;
}

.ctavum__panel {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 20px;
  border-radius: 16px;
  background: #231f28;
}

.ctavum__btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  border: 0;
  border-radius: 12px;
  background: #17141a;
  padding: 16px 20px;
  cursor: pointer;
}

.ctavum__bars {
  display: flex;
  align-items: flex-end;
  gap: 4px;
  height: 40px;
}

.ctavum__bar {
  width: 6px;
  height: 14%;
  border-radius: 4px;
  background: #3ddc97;
}

.ctavum__bar:nth-child(4),
.ctavum__bar:nth-child(5) {
  background: #ff7a5e;
}

.ctavum__label {
  color: #fff7e6;
  font-family: inherit;
  font-weight: 700;
  font-size: 13px;
}

.ctavum__hint {
  color: #9a93a6;
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .ctavum__panel {
    padding: 16px;
    gap: 12px;
  }
  .ctavum__btn {
    padding: 12px 16px;
  }
  .ctavum__bars {
    height: 34px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ctavum__bar {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('ctavum');
  var btn = document.getElementById('ctavumBtn');
  var barsWrap = document.getElementById('ctavumBars');
  var N = 5;
  var bars = [];
  for (var i = 0; i < N; i++) {
    var el = document.createElement('span');
    el.className = 'ctavum__bar';
    barsWrap.appendChild(el);
    bars.push({ el: el, h: 0.14 });
  }

  // 계산 겹: 클릭마다 막대별 목표 높이 값을 서로 다른 난수로 정하고, 매 프레임
  // 현재 높이에서 목표까지 감쇠(DECAY)시켜 실제 VU 미터의 피크-감쇠 곡선을 흉내낸다.
  var DECAY = 0.14, MIN_H = 0.14;
  var raf = null;

  function render() {
    for (var i = 0; i < N; i++) {
      bars[i].el.style.height = (bars[i].h * 100).toFixed(1) + '%';
    }
  }
  function tick() {
    var moving = false;
    for (var i = 0; i < N; i++) {
      var b = bars[i];
      var diff = MIN_H - b.h;
      if (b.h > MIN_H) {
        b.h += diff * DECAY;
        if (b.h - MIN_H > 0.004) { moving = true; } else { b.h = MIN_H; }
      }
    }
    render();
    if (moving) { raf = requestAnimationFrame(tick); } else { raf = null; }
  }
  function hit() {
    for (var i = 0; i < N; i++) {
      bars[i].h = Math.max(bars[i].h, MIN_H + Math.random() * 0.82);
    }
    render();
    if (!raf) { raf = requestAnimationFrame(tick); }
  }

  function wireReal() {
    btn.addEventListener('click', function () { root.classList.remove('is-demo'); stopAutoplay(); hit(); });
  }
  wireReal();
  render();

  var autoplayTimer = null;
  function stopAutoplay() { if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { hit(); autoplayTimer = setInterval(hit, 420); }
})();

import { useEffect, useRef } from "react";
import styles from "./CtaBtnVuMeterTap.module.scss";

export type CtaBtnVuMeterTapProps = {
  color?: string;
};

const N = 5;

export default function CtaBtnVuMeterTap({
  color = "#4cd4a6",
}: CtaBtnVuMeterTapProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const btn = root.querySelector<HTMLButtonElement>(`.${styles.btn}`);
    const barsWrap = root.querySelector<HTMLSpanElement>(`.${styles.bars}`);
    const hint = root.querySelector<HTMLSpanElement>(`.${styles.hint}`);
    if (!btn || !barsWrap || !hint) return;

    const bars: { el: HTMLSpanElement; h: number }[] = [];
    for (let i = 0; i < N; i++) {
      const el = document.createElement("span");
      el.className = styles.bar;
      barsWrap.appendChild(el);
      bars.push({ el, h: 0.14 });
    }

    // 계산 겹: 클릭마다 막대별 목표 높이 값을 서로 다른 난수로 정하고, 매 프레임
    // 현재 높이에서 목표까지 감쇠(DECAY)시켜 실제 VU 미터의 피크-감쇠 곡선을 흉내낸다.
    const DECAY = 0.14;
    const MIN_H = 0.14;
    let raf: number | null = null;

    function render() {
      for (let i = 0; i < N; i++) {
        bars[i].el.style.height = (bars[i].h * 100).toFixed(1) + "%";
      }
    }
    function tick() {
      let moving = false;
      for (let i = 0; i < N; i++) {
        const b = bars[i];
        const diff = MIN_H - b.h;
        if (b.h > MIN_H) {
          b.h += diff * DECAY;
          if (b.h - MIN_H > 0.004) { moving = true; } else { b.h = MIN_H; }
        }
      }
      render();
      raf = moving ? requestAnimationFrame(tick) : null;
    }
    function hit() {
      for (let i = 0; i < N; i++) {
        bars[i].h = Math.max(bars[i].h, MIN_H + Math.random() * 0.82);
      }
      render();
      if (raf === null) { raf = requestAnimationFrame(tick); }
    }

    function onClick() { stopAutoplay(); hit(); }
    btn.addEventListener("click", onClick);
    render();

    let autoplayTimer: number | null = null;
    function stopAutoplay() { if (autoplayTimer !== null) { window.clearInterval(autoplayTimer); autoplayTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { hit(); autoplayTimer = window.setInterval(hit, 420); }

    return () => {
      stopAutoplay();
      if (raf !== null) cancelAnimationFrame(raf);
      btn.removeEventListener("click", onClick);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.panel}>
        <button className={styles.btn} type="button" style={{ background: color }}>
          <span className={styles.bars} />
          <span className={styles.label}>알림음 켜기</span>
        </button>
        <span className={styles.hint}>클릭할 때마다 막대가 튀었다가 가라앉습니다</span>
      </div>
    </div>
  );
}