06Number percent

<main class="stage">
  <div class="counter" role="status" aria-label="Reading progress">
    <span class="counter__num is-demo" aria-hidden="true"></span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$color: $subject-ink;                               // 숫자 색
$duration: $dur-loop;
$easing: linear;                                    // 스크롤과 1:1로 움직이니 linear 가 맞다

@include stage($stage-yellow);

// 정수라야 애니메이션 중간값도 정수로 보간된다 (029 와 같은 기법)
@property --num {
  syntax: '<integer>';
  initial-value: 0;
  inherits: false;
}

.counter {
  position: fixed;
  top: $sp-6; right: $sp-6;
}

.counter__num {
  --num: 0;
  counter-reset: num var(--num);
  display: block;
  font-weight: 800;
  font-size: clamp(26px, 8vw, 36px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  color: $color;

  &::before { content: counter(num) '%'; }

  // 실제 사용: 전체 문서를 스크롤한 비율이 그대로 숫자가 된다
  @supports (animation-timeline: scroll()) {
    animation: count-up $easing both;
    animation-timeline: scroll(root);
  }
}
@keyframes count-up { from { --num: 0; } to { --num: 100; } }

.counter__num.is-demo { animation: count-up-loop $duration $easing infinite; }
@keyframes count-up-loop {
  0%   { --num: 0; }
  92%  { --num: 100; }
  100% { --num: 100; }
}

@media (prefers-reduced-motion: reduce) {
  .counter__num, .counter__num.is-demo { animation: none !important; --num: 100; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

@property --num {
  syntax: "<integer>";
  initial-value: 0;
  inherits: false;
}
.counter {
  position: fixed;
  top: 24px;
  right: 24px;
}

.counter__num {
  --num: 0;
  counter-reset: num var(--num);
  display: block;
  font-weight: 800;
  font-size: clamp(26px, 8vw, 36px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  color: #17141a;
}
.counter__num::before {
  content: counter(num) "%";
}
@supports (animation-timeline: scroll()) {
  .counter__num {
    animation: count-up linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes count-up {
  from {
    --num: 0;
  }
  to {
    --num: 100;
  }
}
.counter__num.is-demo {
  animation: count-up-loop 2s linear infinite;
}

@keyframes count-up-loop {
  0% {
    --num: 0;
  }
  92% {
    --num: 100;
  }
  100% {
    --num: 100;
  }
}
@media (prefers-reduced-motion: reduce) {
  .counter__num, .counter__num.is-demo {
    animation: none !important;
    --num: 100;
  }
}

import { useEffect, useState } from "react";
import styles from "./PercentCounter.module.scss";

export type PercentCounterProps = {
  /** 숫자 색 */
  color?: string;
};

// 실제 쓰임: 스크롤 진행률을 그대로 정수 퍼센트로 보여준다.
export default function PercentCounter({ color = "#17141a" }: PercentCounterProps) {
  const [percent, setPercent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setPercent(max > 0 ? Math.min(100, Math.round((window.scrollY / max) * 100)) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  return (
    <div className={styles.counter} role="status" aria-label="Reading progress">
      <span className={styles.num} style={{ color }}>{percent}%</span>
    </div>
  );
}