09Dotted-to-solid morph

<main class="stage">
  <a class="link is-demo" href="#">Read the next post</a>
</main>

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

// ── 변수 3개 ─────────────────────────────
$duration: $dur-base;
$easing:   $ease-out;
$color:    $subject-cream;

// ── 데모 무대 ───────────────────────────────
@include stage($stage-ink);

// text-decoration-style 은 애니메이션이 안 되는 이산값이라, 점선 막대·실선 막대 두 개를 같은 자리에 겹쳐 opacity 로 교차한다
.link {
  position: relative;
  display: inline-block;
  padding: $sp-2 $sp-1;
  color: $color;
  text-decoration: none;
  font-weight: 700; font-size: clamp(18px, 5vw, 26px); line-height: 1.2;

  &::before, &::after {
    content: "";
    position: absolute;
    left: 0; right: 0; bottom: 0;
    height: 2px;
    transition: opacity $duration $easing;
  }
  &::before {
    background-image: repeating-linear-gradient(90deg, currentColor 0 3px, transparent 3px 7px);
    opacity: 1;
  }
  &::after {
    background: currentColor;
    opacity: 0;
  }
  &:hover::before, &:focus-visible::before { opacity: 0; }
  &:hover::after,  &:focus-visible::after  { opacity: 1; }

  &.is-demo::before { animation: dotted-fade $dur-loop $easing infinite; }
  &.is-demo::after  { animation: solid-fade  $dur-loop $easing infinite; }
}

@keyframes dotted-fade {
  0%, 100%  { opacity: 1; }
  35%, 60%  { opacity: 0; }
}
@keyframes solid-fade {
  0%, 100%  { opacity: 0; }
  35%, 60%  { opacity: 1; }
}

@media (prefers-reduced-motion: reduce) {
  .link::before, .link::after, .link.is-demo::before, .link.is-demo::after { transition: none; animation: none; }
  .link:hover::before, .link:focus-visible::before { opacity: 0; }
  .link:hover::after,  .link:focus-visible::after  { opacity: 1; }
}

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);
}

.link {
  position: relative;
  display: inline-block;
  padding: 8px 4px;
  color: #fff7e6;
  text-decoration: none;
  font-weight: 700;
  font-size: clamp(18px, 5vw, 26px);
  line-height: 1.2;
}
.link::before, .link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  transition: opacity 300ms ease-out;
}
.link::before {
  background-image: repeating-linear-gradient(90deg, currentColor 0 3px, transparent 3px 7px);
  opacity: 1;
}
.link::after {
  background: currentColor;
  opacity: 0;
}
.link:hover::before, .link:focus-visible::before {
  opacity: 0;
}
.link:hover::after, .link:focus-visible::after {
  opacity: 1;
}
.link.is-demo::before {
  animation: dotted-fade 2s ease-out infinite;
}
.link.is-demo::after {
  animation: solid-fade 2s ease-out infinite;
}

@keyframes dotted-fade {
  0%, 100% {
    opacity: 1;
  }
  35%, 60% {
    opacity: 0;
  }
}
@keyframes solid-fade {
  0%, 100% {
    opacity: 0;
  }
  35%, 60% {
    opacity: 1;
  }
}
@media (prefers-reduced-motion: reduce) {
  .link::before, .link::after, .link.is-demo::before, .link.is-demo::after {
    transition: none;
    animation: none;
  }
  .link:hover::before, .link:focus-visible::before {
    opacity: 0;
  }
  .link:hover::after, .link:focus-visible::after {
    opacity: 1;
  }
}

document.querySelectorAll('.link').forEach(function (b) {
  b.addEventListener('pointerenter', function () { b.classList.remove('is-demo'); });
  b.addEventListener('click', function (e) { e.preventDefault(); });
});

import type { CSSProperties, ReactNode } from "react";
import styles from "./DottedMorphUnderline.module.scss";

export type DottedMorphUnderlineProps = { children: ReactNode; href: string; duration?: number; color?: string };

export default function DottedMorphUnderline({ children, href, duration = 300, color = "currentColor" }: DottedMorphUnderlineProps) {
  const vars = { "--duration": `${duration}ms`, "--color": color } as CSSProperties;
  return (
    <a className={styles.link} href={href} style={vars}>
      {children}
    </a>
  );
}