07Sequential reveal — a button whose second phrase appears character by character following an order value on hover

<main class="stage">
<div class="ctatwr is-demo" id="ctatwr">
  <div class="ctatwr__panel">
    <button class="ctatwr__btn" id="ctatwrBtn" type="button">
      <span class="ctatwr__phrase ctatwr__phrase--first" id="ctatwrFirst">Learn more</span>
      <span class="ctatwr__phrase ctatwr__phrase--second" id="ctatwrSecond" aria-hidden="true"></span>
    </button>
    <span class="ctatwr__hint">Hover and the second phrase appears character by character</span>
  </div>
</div>
</main>

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

// 계산 겹(글자별 가변 지연)은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-ink);

.stage { position: relative; }

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

.ctatwr__btn {
  position: relative;
  border: 0;
  border-radius: $r-control;
  background: $subject-mint;
  color: $subject-ink;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  padding: $sp-4 $sp-5;
  min-width: 168px;
  cursor: pointer;
  display: grid;
}

.ctatwr__phrase {
  grid-area: 1 / 1;
}

.ctatwr__phrase--first {
  opacity: 1;
  transition: opacity $dur-quick $ease-out;
}

.ctatwr__phrase--first.is-hidden {
  opacity: 0;
}

.ctatwr__phrase--second {
  display: flex;
}

.ctatwr__phrase--second span {
  opacity: 0;
  transform: translateY(3px);
  transition: opacity $dur-instant $ease-out, transform $dur-instant $ease-out;
}

.ctatwr__phrase--second.is-shown span {
  opacity: 1;
  transform: translateY(0);
}

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

@media (max-width: 340px) {
  .ctatwr__panel { padding: $sp-4; gap: $sp-3; }
  .ctatwr__btn { padding: $sp-3 $sp-4; font-size: 14px; min-width: 148px; }
}

@media (prefers-reduced-motion: reduce) {
  .ctatwr__phrase--second span { 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;
}

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

.ctatwr__btn {
  position: relative;
  border: 0;
  border-radius: 12px;
  background: #4cd4a6;
  color: #17141a;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  padding: 16px 20px;
  min-width: 168px;
  cursor: pointer;
  display: grid;
}

.ctatwr__phrase {
  grid-area: 1/1;
}

.ctatwr__phrase--first {
  opacity: 1;
  transition: opacity 220ms ease-out;
}

.ctatwr__phrase--first.is-hidden {
  opacity: 0;
}

.ctatwr__phrase--second {
  display: flex;
}

.ctatwr__phrase--second span {
  opacity: 0;
  transform: translateY(3px);
  transition: opacity 140ms ease-out, transform 140ms ease-out;
}

.ctatwr__phrase--second.is-shown span {
  opacity: 1;
  transform: translateY(0);
}

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

@media (max-width: 340px) {
  .ctatwr__panel {
    padding: 16px;
    gap: 12px;
  }
  .ctatwr__btn {
    padding: 12px 16px;
    font-size: 14px;
    min-width: 148px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ctatwr__phrase--second span {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('ctatwr');
  var btn = document.getElementById('ctatwrBtn');
  var first = document.getElementById('ctatwrFirst');
  var second = document.getElementById('ctatwrSecond');
  var TEXT = '30% off right now';

  // 계산 겹: 각 글자의 등장 지연 값을 순서(i) 의 0.82제곱에 비례하게 계산해
  // 뒤로 갈수록 지연 간격이 좁아지는(가속하는) 타자기 리듬을 만든다.
  var BASE = 70;
  TEXT.split('').forEach(function (ch, i) {
    var span = document.createElement('span');
    span.textContent = ch === ' ' ? ' ' : ch;
    span.style.transitionDelay = (Math.pow(i, 0.82) * BASE).toFixed(0) + 'ms';
    second.appendChild(span);
  });
  var maxDelay = Math.pow(TEXT.length - 1, 0.82) * BASE + 260;

  function reveal() {
    second.classList.add('is-shown');
    first.classList.add('is-hidden');
  }
  function hide() {
    second.classList.remove('is-shown');
    first.classList.remove('is-hidden');
  }

  function wireReal() {
    btn.addEventListener('mouseenter', function () { root.classList.remove('is-demo'); stopAutoplay(); reveal(); });
    btn.addEventListener('mouseleave', hide);
    btn.addEventListener('focus', function () { root.classList.remove('is-demo'); stopAutoplay(); reveal(); });
    btn.addEventListener('blur', hide);
  }
  wireReal();

  var shown = false, autoplayTimer = null;
  function autoplayTick() { shown = !shown; if (shown) { reveal(); } else { hide(); } }
  function stopAutoplay() { if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { autoplayTimer = setInterval(autoplayTick, maxDelay + 500); }
})();

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

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

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

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const btn = root.querySelector<HTMLButtonElement>(`.${styles.btn}`);
    const first = root.querySelector<HTMLSpanElement>(`.${styles.first}`);
    const second = root.querySelector<HTMLSpanElement>(`.${styles.second}`);
    if (!btn || !first || !second) return;
    const TEXT = "지금 30% 할인중";

    // 계산 겹: 각 글자의 등장 지연 값을 순서(i) 의 0.82제곱에 비례하게 계산해
    // 뒤로 갈수록 지연 간격이 좁아지는(가속하는) 타자기 리듬을 만든다.
    const BASE = 70;
    TEXT.split("").forEach((ch, i) => {
      const span = document.createElement("span");
      span.textContent = ch === " " ? " " : ch;
      span.style.transitionDelay = (Math.pow(i, 0.82) * BASE).toFixed(0) + "ms";
      second.appendChild(span);
    });
    const maxDelay = Math.pow(TEXT.length - 1, 0.82) * BASE + 260;

    function reveal() { second!.classList.add(styles.isShown); first!.classList.add(styles.isHidden); }
    function hide() { second!.classList.remove(styles.isShown); first!.classList.remove(styles.isHidden); }

    function onEnter() { stopAutoplay(); reveal(); }
    btn.addEventListener("mouseenter", onEnter);
    btn.addEventListener("mouseleave", hide);
    btn.addEventListener("focus", onEnter);
    btn.addEventListener("blur", hide);

    let shown = false;
    let autoplayTimer: number | null = null;
    function autoplayTick() { shown = !shown; if (shown) { reveal(); } else { hide(); } }
    function stopAutoplay() { if (autoplayTimer !== null) { window.clearInterval(autoplayTimer); autoplayTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoplayTimer = window.setInterval(autoplayTick, maxDelay + 500); }

    return () => {
      stopAutoplay();
      btn.removeEventListener("mouseenter", onEnter);
      btn.removeEventListener("mouseleave", hide);
      btn.removeEventListener("focus", onEnter);
      btn.removeEventListener("blur", hide);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.panel}>
        <button className={styles.btn} type="button" style={{ background: color }}>
          <span className={styles.first}>더 알아보기</span>
          <span className={styles.second} aria-hidden="true" />
        </button>
        <span className={styles.hint}>호버하면 두 번째 문구가 한 글자씩 나타납니다</span>
      </div>
    </div>
  );
}