09Stat counter — a number recalculated every frame up to a target value

<main class="stage" id="stage">
  <section class="stats" id="stats">
    <div class="stat">
      <p class="stat__num" id="stat-1" data-target="12800" data-suffix="+">0</p>
      <p class="stat__label">Total users</p>
    </div>
    <div class="stat">
      <p class="stat__num" id="stat-2" data-target="98" data-suffix="%">0</p>
      <p class="stat__label">Satisfaction</p>
    </div>
    <div class="stat">
      <p class="stat__num" id="stat-3" data-target="42">0</p>
      <p class="stat__label">Integrations</p>
    </div>
  </section>
</main>

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

$color: $subject-blue-light;

@include stage($stage-ink);

.stats {
  display: flex;
  gap: $sp-8;
  flex-wrap: wrap;
  justify-content: center;
  text-align: center;
}

.stat__num {
  margin: 0;
  color: $color;
  font-weight: 800;
  font-size: clamp(24px, 8vmin, 34px);
  line-height: 1.2;
  font-variant-numeric: tabular-nums;
}

.stat__label {
  margin: $sp-2 0 0;
  color: $stage-paper;
  font-size: 12px;
  line-height: 1.5;
}

@media (max-width: 340px) {
  .stats { gap: $sp-5; }
}

// 카운트업 자체는 JS(rAF)가 matchMedia 로 직접 분기 — 여기는 CSS 트랜지션이 없어 no-op.
@media (prefers-reduced-motion: reduce) {
  .stat__num { animation: none; transition: none; }
}

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);
}

.stats {
  display: flex;
  gap: 32px;
  flex-wrap: wrap;
  justify-content: center;
  text-align: center;
}

.stat__num {
  margin: 0;
  color: #5b8cf8;
  font-weight: 800;
  font-size: clamp(24px, 8vmin, 34px);
  line-height: 1.2;
  font-variant-numeric: tabular-nums;
}

.stat__label {
  margin: 8px 0 0;
  color: #ffffff;
  font-size: 12px;
  line-height: 1.5;
}

@media (max-width: 340px) {
  .stats {
    gap: 20px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .stat__num {
    animation: none;
    transition: none;
  }
}

// 화면에 보이는 순간부터 0에서 목표 값까지, 매 프레임(rAF) 다시 계산해 textContent 를 갱신한다.
// 계산 겹: 경과 시간 비율 -> 완화 함수 -> 현재 값(0~목표) -> 문자열 표시. 자동 재생(리스너 없음).
(function () {
  var COUNT_DURATION_MS = 1700;
  var nums = document.querySelectorAll('.stat__num');
  var reduceMotion = window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function easeOutCubic(t) {
    return 1 - Math.pow(1 - t, 3);
  }

  function format(n) {
    return Math.round(n).toLocaleString('ko-KR');
  }

  function run(el) {
    var target = Number(el.getAttribute('data-target')) || 0;
    var suffix = el.getAttribute('data-suffix') || '';
    if (reduceMotion) {
      el.textContent = format(target) + suffix;
      return;
    }
    var start = null;
    function step(ts) {
      if (start === null) start = ts;
      var elapsed = ts - start;
      var t = Math.min(1, elapsed / COUNT_DURATION_MS);
      var value = target * easeOutCubic(t);
      el.textContent = format(value) + suffix;
      if (t < 1) {
        window.requestAnimationFrame(step);
      }
    }
    window.requestAnimationFrame(step);
  }

  nums.forEach(run);
})();

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

// 화면에 보이는 순간부터 0에서 목표 값까지, 매 프레임(rAF) 다시 계산해 textContent 를 갱신한다.
// 계산 겹: 경과 시간 비율 -> 완화 함수 -> 현재 값(0~목표) -> 문자열 표시. 자동 재생(리스너 없음).
const COUNT_DURATION_MS = 1700;

const STATS = [
  { id: "stat-1", target: 12800, suffix: "+", label: "누적 사용자" },
  { id: "stat-2", target: 98, suffix: "%", label: "만족도" },
  { id: "stat-3", target: 42, suffix: "", label: "연동 서비스" },
];

function easeOutCubic(t: number) {
  return 1 - Math.pow(1 - t, 3);
}

function format(n: number) {
  return Math.round(n).toLocaleString("ko-KR");
}

export default function StatsCounter() {
  const numRefs = useRef<Array<HTMLParagraphElement | null>>([]);

  useEffect(() => {
    const reduceMotion =
      window.matchMedia && window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    const rafIds: number[] = [];

    const refs = numRefs.current!;

    STATS.forEach((stat, i) => {
      const el = refs[i];
      if (!el) return;

      if (reduceMotion) {
        el.textContent = format(stat.target) + stat.suffix;
        return;
      }

      let start: number | null = null;
      function step(ts: number) {
        if (start === null) start = ts;
        const elapsed = ts - start;
        const t = Math.min(1, elapsed / COUNT_DURATION_MS);
        const value = stat.target * easeOutCubic(t);
        el!.textContent = format(value) + stat.suffix;
        if (t < 1) {
          rafIds[i] = window.requestAnimationFrame(step);
        }
      }
      rafIds[i] = window.requestAnimationFrame(step);
    });

    return () => rafIds.forEach((id) => window.cancelAnimationFrame(id));
  }, []);

  return (
    <main className={styles.stage}>
      <section className={styles.stats}>
        {STATS.map((stat, i) => (
          <div key={stat.id} className={styles.stat}>
            <p
              className={styles.stat__num}
              ref={(node: HTMLParagraphElement | null) => {
                numRefs.current![i] = node;
              }}
            >
              0
            </p>
            <p className={styles.stat__label}>{stat.label}</p>
          </div>
        ))}
      </section>
    </main>
  );
}