06Category tree expand — a list recomputing height from child count

<main class="stage">
  <div class="tree">
    <button class="tree__toggle" id="toggle" type="button" aria-expanded="false" aria-controls="list">
      <svg class="tree__caret" viewBox="0 0 256 256" width="14" height="14" aria-hidden="true"><g fill="currentColor"><path d="m208 96l-80 80l-80-80Z" opacity=".2"/><path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z"/></g></svg>
      Category
    </button>
    <ul class="tree__list is-demo" id="list">
      <li>Women's clothing (128)</li>
      <li>Men's clothing (86)</li>
      <li>Accessories (42)</li>
    </ul>
  </div>
</main>

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

$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-ink;

@include stage($stage-yellow);

.tree {
  box-sizing: border-box;
  width: min(80vw, 220px);
  padding: $sp-3 $sp-4;
  border-radius: $r-card;
  background: $subject-cream;
  color: $color;
}

.tree__toggle {
  display: flex;
  align-items: center;
  gap: $sp-2;
  width: 100%;
  border: 0;
  background: transparent;
  padding: 0;
  color: $color;
  font-family: inherit;
  font-weight: 600;
  font-size: 13px;
  line-height: 1.4;
  cursor: pointer;
}

.tree__caret {
  flex: 0 0 auto;
  transition: transform $duration $easing;
}

.tree__toggle[aria-expanded="true"] .tree__caret {
  transform: rotate(180deg);
}

.tree__list {
  margin: 0;
  padding: 0;
  list-style: none;
  overflow: hidden;
  height: 0;
  transition: height $duration $easing;
}

.tree__list.is-open {
  height: var(--tree-height, auto);
}

.tree__list li {
  padding: $sp-2 $sp-1 $sp-2 $sp-6;
  font-size: 12px;
  line-height: 1.4;
  color: rgba($color, .8);
}

.tree__list.is-demo {
  animation-name: tree-loop;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}

@keyframes tree-loop {
  0%, 18% { height: 0; }
  45%, 75% { height: var(--tree-height, 100px); }
  100% { height: 0; }
}

@media (max-width: 340px) {
  .tree { width: 84vw; padding: $sp-2 $sp-3; }
  .tree__list li { padding-left: $sp-4; }
}

@media (prefers-reduced-motion: reduce) {
  .tree__list, .tree__caret { transition: none; }
  .tree__list.is-demo { animation: none; height: var(--tree-height, auto); }
}

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);
}

.tree {
  box-sizing: border-box;
  width: min(80vw, 220px);
  padding: 12px 16px;
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
}

.tree__toggle {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
  border: 0;
  background: transparent;
  padding: 0;
  color: #17141a;
  font-family: inherit;
  font-weight: 600;
  font-size: 13px;
  line-height: 1.4;
  cursor: pointer;
}

.tree__caret {
  flex: 0 0 auto;
  transition: transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.tree__toggle[aria-expanded=true] .tree__caret {
  transform: rotate(180deg);
}

.tree__list {
  margin: 0;
  padding: 0;
  list-style: none;
  overflow: hidden;
  height: 0;
  transition: height 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.tree__list.is-open {
  height: var(--tree-height, auto);
}

.tree__list li {
  padding: 8px 4px 8px 24px;
  font-size: 12px;
  line-height: 1.4;
  color: rgba(23, 20, 26, 0.8);
}

.tree__list.is-demo {
  animation-name: tree-loop;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes tree-loop {
  0%, 18% {
    height: 0;
  }
  45%, 75% {
    height: var(--tree-height, 100px);
  }
  100% {
    height: 0;
  }
}
@media (max-width: 340px) {
  .tree {
    width: 84vw;
    padding: 8px 12px;
  }
  .tree__list li {
    padding-left: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .tree__list, .tree__caret {
    transition: none;
  }
  .tree__list.is-demo {
    animation: none;
    height: var(--tree-height, auto);
  }
}

// 하위 목록의 실제 렌더 높이(scrollHeight)를 재서 --tree-height 로 저장(setProperty)해 두고,
// 펼침 상태는 그 값을 height 로 삼아 transition·keyframe 이 0 에서 그 값까지 보간한다.
// 실제 클릭: aria-expanded 를 뒤집고 목록을 펼치거나 접는다.
(function () {
  var toggle = document.getElementById('toggle');
  var list = document.getElementById('list');
  if (!toggle || !list) return;

  function measure() {
    list.style.setProperty('--tree-height', list.scrollHeight + 'px');
  }
  measure();

  toggle.addEventListener('click', function () {
    list.classList.remove('is-demo');
    measure();
    var open = list.classList.toggle('is-open');
    toggle.setAttribute('aria-expanded', String(open));
  });

  window.addEventListener('resize', measure);
})();

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

// 하위 목록의 실제 렌더 높이(scrollHeight)를 재서 --tree-height 로 저장(setProperty)해 두고,
// 펼침 상태는 그 값을 height 로 삼아 transition·keyframe 이 0 에서 그 값까지 보간한다.
// 실제 클릭: aria-expanded 를 뒤집고 목록을 펼치거나 접는다.
export default function CategoryTreeExpand() {
  const toggleRef = useRef<HTMLButtonElement>(null);
  const listRef = useRef<HTMLUListElement>(null);

  useEffect(() => {
    const toggle = toggleRef.current;
    const list = listRef.current;
    if (!toggle || !list) return;

    function measure() {
      list!.style.setProperty("--tree-height", list!.scrollHeight + "px");
    }
    measure();

    function onClick() {
      list!.classList.remove(styles["is-demo"]);
      measure();
      const open = list!.classList.toggle(styles["is-open"]);
      toggle!.setAttribute("aria-expanded", String(open));
    }

    toggle.addEventListener("click", onClick);
    window.addEventListener("resize", measure);
    return () => {
      toggle.removeEventListener("click", onClick);
      window.removeEventListener("resize", measure);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.tree}>
        <button
          ref={toggleRef}
          className={styles.tree__toggle}
          type="button"
          aria-expanded="false"
          aria-controls="list"
        >
          <svg className={styles.tree__caret} viewBox="0 0 256 256" width="14" height="14" aria-hidden="true">
            <g fill="currentColor">
              <path d="m208 96l-80 80l-80-80Z" opacity=".2" />
              <path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z" />
            </g>
          </svg>
          카테고리
        </button>
        <ul ref={listRef} id="list" className={`${styles.tree__list} ${styles["is-demo"]}`}>
          <li>여성 의류 (128)</li>
          <li>남성 의류 (86)</li>
          <li>액세서리 (42)</li>
        </ul>
      </div>
    </main>
  );
}