05Prime-glow marker — computing a primality check so only qualifying numbers glow

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <ol class="prime-list" id="list" start="1">
    <li>Variables and types</li>
    <li>Conditions and loops</li>
    <li>Functions and scope</li>
    <li>Arrays and objects</li>
    <li>Async handling</li>
    <li>Module system</li>
    <li>Writing tests</li>
  </ol>
  <button class="shift" id="shift" type="button">Shift the start number by one</button>
</div>
</main>

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

// 계산 겹은 index.html 의 isPrime() 시행 나눗셈 판정에 있다 — 여기는 번호 상자·글로우 애니메이션만 맡는다.
// ::marker 는 box-shadow(글로우)·animation 을 지원하지 않는다(color·content·font 뿐) — list-style:none 으로
// 네이티브 번호를 지우고 counter() 값을 ::before 콘텐츠로 다시 그려 그 위에 글로우를 건다.
@include stage($stage-paper);

.prime-list {
  list-style: none;
  counter-reset: item;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  width: 230px;
}

.prime-list li {
  counter-increment: item;
  position: relative;
  padding-left: 32px;
  min-height: 22px;
  display: flex;
  align-items: center;
  color: $subject-ink;
  font-size: 12px;
}

.prime-list li::before {
  content: counter(item);
  position: absolute;
  left: 0;
  top: 50%;
  width: 22px;
  height: 22px;
  margin-top: -11px;
  border-radius: 50%;
  background: $subject-blue-deep;
  color: $subject-cream;
  font-size: 11px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 0 0 0 rgba($subject-blue-deep, 0);
}

.prime-list li.is-prime::before {
  animation: primePulse $dur-loop $ease-out infinite;
}

@keyframes primePulse {
  0%, 100% { box-shadow: 0 0 0 0 rgba($subject-blue-deep, .55); }
  50% { box-shadow: 0 0 0 7px rgba($subject-blue-deep, 0); }
}

.shift {
  appearance: none;
  border: none;
  margin-top: $sp-4;
  padding: $sp-2 $sp-4;
  border-radius: $r-control;
  background: $subject-blue-deep;
  color: $subject-cream;
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: transform $dur-instant $ease-out;

  &:hover { transform: translateY(-1px); }
  &:active { transform: scale(.96); }
  &:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 2px; }
}

@media (max-width: 340px) {
  .prime-list {
    width: 260px;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: $sp-1;
  }
  .prime-list li { font-size: 10px; min-height: 20px; padding-left: 24px; }
  .prime-list li::before { width: 18px; height: 18px; margin-top: -9px; font-size: 10px; }
  .shift { margin-top: $sp-2; padding: $sp-1 $sp-3; }
}

@media (prefers-reduced-motion: reduce) {
  .prime-list li.is-prime::before { animation: none; box-shadow: 0 0 0 4px rgba($subject-blue-deep, .35); }
  .shift { transition: none; }
}

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

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

.prime-list {
  list-style: none;
  counter-reset: item;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 230px;
}

.prime-list li {
  counter-increment: item;
  position: relative;
  padding-left: 32px;
  min-height: 22px;
  display: flex;
  align-items: center;
  color: #17141a;
  font-size: 12px;
}

.prime-list li::before {
  content: counter(item);
  position: absolute;
  left: 0;
  top: 50%;
  width: 22px;
  height: 22px;
  margin-top: -11px;
  border-radius: 50%;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 11px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 0 0 0 rgba(10, 79, 232, 0);
}

.prime-list li.is-prime::before {
  animation: primePulse 2s ease-out infinite;
}

@keyframes primePulse {
  0%, 100% {
    box-shadow: 0 0 0 0 rgba(10, 79, 232, 0.55);
  }
  50% {
    box-shadow: 0 0 0 7px rgba(10, 79, 232, 0);
  }
}
.shift {
  appearance: none;
  border: none;
  margin-top: 16px;
  padding: 8px 16px;
  border-radius: 12px;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 140ms ease-out;
}
.shift:hover {
  transform: translateY(-1px);
}
.shift:active {
  transform: scale(0.96);
}
.shift:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

@media (max-width: 340px) {
  .prime-list {
    width: 260px;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 4px;
  }
  .prime-list li {
    font-size: 10px;
    min-height: 20px;
    padding-left: 24px;
  }
  .prime-list li::before {
    width: 18px;
    height: 18px;
    margin-top: -9px;
    font-size: 10px;
  }
  .shift {
    margin-top: 8px;
    padding: 4px 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .prime-list li.is-prime::before {
    animation: none;
    box-shadow: 0 0 0 4px rgba(10, 79, 232, 0.35);
  }
  .shift {
    transition: none;
  }
}

(function () {
  var GLOW_PULSE_MS = 1100;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var wrap = document.getElementById('wrap');
  var list = document.getElementById('list');
  var items = Array.prototype.slice.call(list.querySelectorAll('li'));
  var button = document.getElementById('shift');
  var isDemo = true;
  var start = 1;

  // 계산 겹: 각 항목 번호에 소수 판정을 직접 계산한다 — 미리 정해둔 목록이 아니라 실행마다 다시 돈다.
  function isPrime(n) {
    if (n < 2) return false;
    for (var d = 2; d * d <= n; d++) {
      if (n % d === 0) return false;
    }
    return true;
  }

  function recompute() {
    list.setAttribute('start', String(start));
    items.forEach(function (li, i) {
      var n = start + i;
      li.classList.toggle('is-prime', isPrime(n));
    });
  }

  function human() { if (isDemo) { wrap.classList.remove('is-demo'); isDemo = false; } }

  button.addEventListener('click', function () {
    human();
    start += 1;
    recompute();
  });

  var last = 0;
  var STEP_MS = 900;
  function loop(ts) {
    if (!last) last = ts;
    if (isDemo && !reduce && ts - last >= STEP_MS) {
      last = ts;
      start += 1;
      recompute();
    }
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
  recompute();
})();

// PrimeGlowMarker — vanilla 판(run/373/demo/05-list-style-number-prime-glow/index.html) 의 React 포트.
// ::marker 는 box-shadow(글로우)·animation 을 지원하지 않는다(color·content·font 뿐) — counter() 값을
// ::before 콘텐츠로 다시 그려 그 위에 글로우를 건다. 소수 판정은 매번 직접 계산한다.
import { useEffect, useRef } from "react";
import styles from "./PrimeGlowMarker.module.scss";

type Box<T> = { current: T };

const STEP_MS = 900; // 자동 루프에서 시작 번호를 한 칸 옮기는 간격

const LESSONS = ["변수와 타입", "조건과 반복", "함수와 스코프", "배열과 객체", "비동기 처리", "모듈 시스템", "테스트 작성"];

export default function PrimeGlowMarker() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const listRef = useRef(null) as unknown as Box<HTMLOListElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

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

    const root = rootRef.current;
    const list = listRef.current;
    if (!root || !list) return;

    const items = Array.prototype.slice.call(list.querySelectorAll("li"));
    let isDemo = true;
    let start = 1;

    // 계산 겹: 각 항목 번호에 소수 판정을 직접 계산한다 — 미리 정해둔 목록이 아니라 실행마다 다시 돈다.
    function isPrime(n: number) {
      if (n < 2) return false;
      for (let d = 2; d * d <= n; d++) {
        if (n % d === 0) return false;
      }
      return true;
    }

    function recompute() {
      list!.setAttribute("start", String(start));
      items.forEach(function (li: HTMLElement, i: number) {
        const n = start + i;
        li.classList.toggle("is-prime", isPrime(n));
      });
    }

    function human() { if (isDemo) { root!.classList.remove(styles.isDemo); isDemo = false; } }

    function onClick() {
      human();
      start += 1;
      recompute();
    }
    root!.addEventListener("click", onClick);

    let last = 0;
    function loop(ts: number) {
      if (!last) last = ts;
      if (isDemo && !reduce && ts - last >= STEP_MS) {
        last = ts;
        start += 1;
        recompute();
      }
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);
    recompute();

    return () => {
      root!.removeEventListener("click", onClick);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <ol className={styles.primeList} ref={listRef} start={1}>
          {LESSONS.map(function (l) { return <li key={l}>{l}</li>; })}
        </ol>
        <button className={styles.shift} type="button">시작 번호 한 칸 이동</button>
      </div>
    </main>
  );
}