03Letter-by-letter stagger

<main class="stage">
  <h1 class="letters is-demo">
    <span>H</span><span>E</span><span>L</span><span>L</span><span>O</span>
  </h1>
</main>

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

$duration: $dur-quick;                             // 글자 하나가 튀어오르는 시간
$easing: $ease-pop;                                // 아래에서 튀어오르는 느낌
$stagger: 30ms;                                    // 글자 사이 시차

@include stage($stage-orange);

.letters {
  margin: 0;
  display: flex;
  gap: clamp(2px, 1vw, 6px);
  font-weight: 800; font-size: clamp(24px, 9vw, 40px); line-height: 1; font-family: inherit;
  color: $subject-cream;

  span {
    display: inline-block;
    animation: letter-loop $dur-loop $easing infinite;
  }

  @for $i from 1 through 5 {
    span:nth-child(#{$i}) { animation-delay: ($i - 1) * $stagger; }
  }
}

@keyframes letter-loop {
  0%, 4%    { opacity: 0; transform: translateY(16px); }
  20%, 66%  { opacity: 1; transform: translateY(0); }
  86%, 100% { opacity: 0; transform: translateY(-10px); }
}

@media (prefers-reduced-motion: reduce) {
  .letters span { animation: none; opacity: 1; transform: 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);
}

.letters {
  margin: 0;
  display: flex;
  gap: clamp(2px, 1vw, 6px);
  font-weight: 800;
  font-size: clamp(24px, 9vw, 40px);
  line-height: 1;
  font-family: inherit;
  color: #fff7e6;
}
.letters span {
  display: inline-block;
  animation: letter-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}
.letters span:nth-child(1) {
  animation-delay: 0ms;
}
.letters span:nth-child(2) {
  animation-delay: 30ms;
}
.letters span:nth-child(3) {
  animation-delay: 60ms;
}
.letters span:nth-child(4) {
  animation-delay: 90ms;
}
.letters span:nth-child(5) {
  animation-delay: 120ms;
}

@keyframes letter-loop {
  0%, 4% {
    opacity: 0;
    transform: translateY(16px);
  }
  20%, 66% {
    opacity: 1;
    transform: translateY(0);
  }
  86%, 100% {
    opacity: 0;
    transform: translateY(-10px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .letters span {
    animation: none;
    opacity: 1;
    transform: none;
  }
}

export type LetterStaggerProps = {
  text: string;
  /** 글자 사이 시차 ms (기본 30ms) */
  stagger?: number;
  duration?: number;
  easing?: string;
};

import styles from "./LetterStagger.module.scss";

export default function LetterStagger({ text, stagger = 30 }: LetterStaggerProps) {
  return (
    <h1 className={styles.letters}>
      {[...text].map((ch, i) => (
        <span key={i} style={{ animationDelay: `${i * stagger}ms` }}>
          {ch}
        </span>
      ))}
    </h1>
  );
}