07Footer — a link list recomputing underline width from zero to the text width

<main class="stage" id="stage">
  <footer class="panel is-demo" id="stage-panel">
    <nav class="links">
      <a class="link" href="#">About us</a>
      <a class="link" href="#">Terms of service</a>
      <a class="link" href="#">Privacy policy</a>
      <a class="link" href="#">Contact us</a>
    </nav>
  </footer>
</main>

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

$duration: $dur-base;
$easing: $ease-out;
$color: $subject-cream;

@include stage($stage-orange);

.panel {
  padding: $sp-6 $sp-5;
  border-radius: $r-card;
  background: $subject-ink;
}

.links {
  display: flex;
  flex-wrap: wrap;
  gap: $sp-5;
  justify-content: center;
}

.link {
  position: relative;
  padding-bottom: $sp-1;
  color: $stage-paper;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.6;
  text-decoration: none;
  white-space: nowrap;
}

.link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  height: 2px;
  width: var(--tw, 0px);
  background: $color;
  transition: width $duration $easing;
}

.is-demo .link:nth-child(1)::after { animation: underline-1 $dur-loop steps(1, end) infinite; }
.is-demo .link:nth-child(2)::after { animation: underline-2 $dur-loop steps(1, end) infinite; }
.is-demo .link:nth-child(3)::after { animation: underline-3 $dur-loop steps(1, end) infinite; }
.is-demo .link:nth-child(4)::after { animation: underline-4 $dur-loop steps(1, end) infinite; }

@keyframes underline-1 { 0%, 4% { width: 0; } 12%, 22% { width: 34px; } 30%, 100% { width: 0; } }
@keyframes underline-2 { 0%, 26% { width: 0; } 34%, 44% { width: 52px; } 52%, 100% { width: 0; } }
@keyframes underline-3 { 0%, 48% { width: 0; } 56%, 66% { width: 76px; } 74%, 100% { width: 0; } }
@keyframes underline-4 { 0%, 70% { width: 0; } 78%, 88% { width: 40px; } 96%, 100% { width: 0; } }

@media (max-width: 340px) {
  .links { gap: $sp-3; }
  .link { font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .is-demo .link:nth-child(1)::after,
  .is-demo .link:nth-child(2)::after,
  .is-demo .link:nth-child(3)::after,
  .is-demo .link:nth-child(4)::after {
    animation: none;
    width: 0;
  }
}

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);
}

.panel {
  padding: 24px 20px;
  border-radius: 16px;
  background: #17141a;
}

.links {
  display: flex;
  flex-wrap: wrap;
  gap: 20px;
  justify-content: center;
}

.link {
  position: relative;
  padding-bottom: 4px;
  color: #ffffff;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.6;
  text-decoration: none;
  white-space: nowrap;
}

.link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  height: 2px;
  width: var(--tw, 0px);
  background: #fff7e6;
  transition: width 300ms ease-out;
}

.is-demo .link:nth-child(1)::after {
  animation: underline-1 2s steps(1, end) infinite;
}

.is-demo .link:nth-child(2)::after {
  animation: underline-2 2s steps(1, end) infinite;
}

.is-demo .link:nth-child(3)::after {
  animation: underline-3 2s steps(1, end) infinite;
}

.is-demo .link:nth-child(4)::after {
  animation: underline-4 2s steps(1, end) infinite;
}

@keyframes underline-1 {
  0%, 4% {
    width: 0;
  }
  12%, 22% {
    width: 34px;
  }
  30%, 100% {
    width: 0;
  }
}
@keyframes underline-2 {
  0%, 26% {
    width: 0;
  }
  34%, 44% {
    width: 52px;
  }
  52%, 100% {
    width: 0;
  }
}
@keyframes underline-3 {
  0%, 48% {
    width: 0;
  }
  56%, 66% {
    width: 76px;
  }
  74%, 100% {
    width: 0;
  }
}
@keyframes underline-4 {
  0%, 70% {
    width: 0;
  }
  78%, 88% {
    width: 40px;
  }
  96%, 100% {
    width: 0;
  }
}
@media (max-width: 340px) {
  .links {
    gap: 12px;
  }
  .link {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .is-demo .link:nth-child(1)::after,
  .is-demo .link:nth-child(2)::after,
  .is-demo .link:nth-child(3)::after,
  .is-demo .link:nth-child(4)::after {
    animation: none;
    width: 0;
  }
}

// 포인터가 링크 위로 올라오면 그 글자의 실제 폭 값을 다시 구해 밑줄 너비 값을 0에서 그 값까지 늘린다.
// 계산 겹: 포인터 진입 -> 글자 폭 값(getBoundingClientRect) -> 밑줄 너비 보간. 실사용 포인터 리스너 있음(데모 재생 자체는 고정 시퀀스).
(function () {
  var panel = document.getElementById('stage-panel');
  if (!panel) return;
  var links = panel.querySelectorAll('.link');

  links.forEach(function (link) {
    link.addEventListener('pointerenter', function () {
      panel.classList.remove('is-demo');
      var w = link.getBoundingClientRect().width;
      link.style.setProperty('--tw', w + 'px');
    });
    link.addEventListener('pointerleave', function () {
      link.style.setProperty('--tw', '0px');
    });
  });
})();

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

// 포인터가 링크 위로 올라오면 그 글자의 실제 폭 값을 다시 구해 밑줄 너비 값을 0에서 그 값까지 늘린다.
// 계산 겹: 포인터 진입 -> 글자 폭 값(getBoundingClientRect) -> 밑줄 너비 보간. 실사용 포인터 리스너 있음(데모 재생 자체는 고정 시퀀스).
const LINKS = ["회사소개", "이용약관", "개인정보처리방침", "문의하기"];

export default function FooterLinks() {
  const panelRef = useRef<HTMLElement>(null);

  useEffect(() => {
    const panel = panelRef.current;
    if (!panel) return;
    const links = panel.querySelectorAll<HTMLAnchorElement>(`.${styles.link}`);

    const handlers: Array<() => void> = [];
    links.forEach((link) => {
      const onEnter = () => {
        panel!.classList.remove(styles["is-demo"]);
        const w = link.getBoundingClientRect().width;
        link.style.setProperty("--tw", w + "px");
      };
      const onLeave = () => {
        link.style.setProperty("--tw", "0px");
      };
      link.addEventListener("pointerenter", onEnter);
      link.addEventListener("pointerleave", onLeave);
      handlers.push(() => {
        link.removeEventListener("pointerenter", onEnter);
        link.removeEventListener("pointerleave", onLeave);
      });
    });

    return () => handlers.forEach((off) => off());
  }, []);

  return (
    <main className={styles.stage}>
      <footer ref={panelRef} className={`${styles.panel} ${styles["is-demo"]}`}>
        <nav className={styles.links}>
          {LINKS.map((label) => (
            <a key={label} className={styles.link} href="#">
              {label}
            </a>
          ))}
        </nav>
      </footer>
    </main>
  );
}