05Per-letter split slide

<main class="stage">
  <button class="split is-demo" type="button" aria-label="See details"><span class="split__in" aria-hidden="true"></span></button>
</main>

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

// 변형은 이 세 줄만 바꾼다
$duration: $dur-loop;
$easing:   $ease-spring;
$stagger:  70ms;

@include stage($stage-orange);

.split {
  border: 0;
  cursor: pointer;
  padding: $sp-3 $sp-6;
  border-radius: $r-control;
  background: $subject-cream;
  color: $stage-orange;
  font-family: inherit;
  font-size: clamp(18px, 6vw, 26px);
  font-weight: 800;
}

.split__in { display: inline-flex; }

// 창(1.25em)은 고정이고 그 안의 두 겹이 굴러간다
.split__ch {
  display: inline-block;
  overflow: hidden;
  height: 1.25em;
  line-height: 1.25;
}

.split__ch b { display: block; }
.split__ch i { display: block; font-style: normal; }

.split.is-demo .split__ch b {
  animation: split-roll $duration $easing infinite;
  animation-delay: calc(var(--i) * #{$stagger});
}

// 두 겹이라 -50% 가 정확히 한 줄. 0 으로 돌아와 끝나므로 되감기가 안 보인다
@keyframes split-roll {
  0%,  12% { translate: 0 0; }
  42%, 68% { translate: 0 -50%; }
  100%     { translate: 0 0; }
}

@media (prefers-reduced-motion: reduce) {
  .split.is-demo .split__ch b { animation: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.split {
  border: 0;
  cursor: pointer;
  padding: 12px 24px;
  border-radius: 12px;
  background: #fff7e6;
  color: #ff4d1f;
  font-family: inherit;
  font-size: clamp(18px, 6vw, 26px);
  font-weight: 800;
}

.split__in {
  display: inline-flex;
}

.split__ch {
  display: inline-block;
  overflow: hidden;
  height: 1.25em;
  line-height: 1.25;
}

.split__ch b {
  display: block;
}

.split__ch i {
  display: block;
  font-style: normal;
}

.split.is-demo .split__ch b {
  animation: split-roll 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
  animation-delay: calc(var(--i) * 70ms);
}

@keyframes split-roll {
  0%, 12% {
    translate: 0 0;
  }
  42%, 68% {
    translate: 0 -50%;
  }
  100% {
    translate: 0 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .split.is-demo .split__ch b {
    animation: none;
  }
}

// 실제 동작: aria-label 의 글자를 하나씩 이중으로 쌓고, 글자 번호(--i)를 지연 시간으로 쓴다.
var split = document.querySelector('.split');
var box = split.querySelector('.split__in');
var text = split.getAttribute('aria-label');
for (var i = 0; i < text.length; i++) {
  var cell = document.createElement('span');
  var roll = document.createElement('b');
  cell.className = 'split__ch';
  cell.style.setProperty('--i', i);
  for (var k = 0; k < 2; k++) {
    var face = document.createElement('i');
    face.textContent = text[i] === ' ' ? ' ' : text[i];
    roll.appendChild(face);
  }
  cell.appendChild(roll);
  box.appendChild(cell);
}

import type { CSSProperties } from "react";
import styles from "./SplitTextButton.module.scss";

export type SplitTextButtonProps = {
  label?: string;
  duration?: number;
  easing?: string;
  stagger?: number;
};

type CellVars = CSSProperties & { "--i"?: number };
type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--stagger"?: string };

export default function SplitTextButton({
  label = "See details",
  duration = 2000,
  easing = "cubic-bezier(.2,.8,.2,1)",
  stagger = 70,
}: SplitTextButtonProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--stagger": `${stagger}ms` };
  const chars = label.split("");

  return (
    <button type="button" className={styles.split} style={vars} aria-label={label}>
      <span className={styles.inner} aria-hidden="true">
        {chars.map((ch, i) => {
          const cell: CellVars = { "--i": i };
          return (
            <span className={styles.ch} style={cell} key={`${ch}-${i}`}>
              <b className={styles.roll}>
                <i>{ch === " " ? " " : ch}</i>
                <i>{ch === " " ? " " : ch}</i>
              </b>
            </span>
          );
        })}
      </span>
    </button>
  );
}