04Load-more button morph — a button recomputing its width from the remaining item count

<main class="stage">
<div class="lbm is-demo" id="lbm">
  <ul class="lbm__list" id="lbmList"></ul>
  <button class="lbm__btn" id="lbmBtn" type="button">
    <span class="lbm__label" id="lbmLabel">Load more (24)</span>
  </button>
</div>
</main>

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

// 더 보기 버튼 모핑 — morphTo() 가 라벨의 실측 폭 + 여백을 목표 너비로 삼고,
// 매 프레임 현재 너비를 목표 쪽으로 24% 씩 당기는 lerp(관성)로 버튼 폭을 바꾼다.

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

@include stage($stage-yellow);

.lbm {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
  width: min(100%, 280px);
}

.lbm__list {
  list-style: none;
  margin: 0;
  padding: 0;
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  max-height: 156px;
  overflow: hidden;
}

.lbm__row {
  box-sizing: border-box;
  padding: $sp-2 $sp-3;
  border-radius: $r-sm;
  background: rgba(23, 20, 26, .08);
  color: $color;
  font-weight: 600;
  font-size: 12px;
}

.lbm__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 $sp-5;
  border: 0;
  border-radius: $r-pill;
  background: $color;
  color: $stage-yellow;
  font-family: inherit;
  font-weight: 700;
  font-size: 12px;
  cursor: pointer;
  overflow: hidden;
  white-space: nowrap;
}

.lbm__btn--loading {
  opacity: .82;
  cursor: progress;
}

.lbm__btn--done {
  background: rgba(23, 20, 26, .28);
  cursor: default;
}

.lbm__label {
  display: inline-block;
}

@media (max-width: 340px) {
  .lbm { gap: $sp-1; }
  .lbm__list { max-height: 80px; }
  .lbm__row { font-size: 11px; }
  .lbm__btn { font-size: 11px; height: 36px; }
}

@media (prefers-reduced-motion: reduce) {
  .lbm__btn { transition: none !important; }
}

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);
}

.lbm {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  width: min(100%, 280px);
}

.lbm__list {
  list-style: none;
  margin: 0;
  padding: 0;
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 8px;
  max-height: 156px;
  overflow: hidden;
}

.lbm__row {
  box-sizing: border-box;
  padding: 8px 12px;
  border-radius: 8px;
  background: rgba(23, 20, 26, 0.08);
  color: #17141a;
  font-weight: 600;
  font-size: 12px;
}

.lbm__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 20px;
  border: 0;
  border-radius: 999px;
  background: #17141a;
  color: #ffd23f;
  font-family: inherit;
  font-weight: 700;
  font-size: 12px;
  cursor: pointer;
  overflow: hidden;
  white-space: nowrap;
}

.lbm__btn--loading {
  opacity: 0.82;
  cursor: progress;
}

.lbm__btn--done {
  background: rgba(23, 20, 26, 0.28);
  cursor: default;
}

.lbm__label {
  display: inline-block;
}

@media (max-width: 340px) {
  .lbm {
    gap: 4px;
  }
  .lbm__list {
    max-height: 80px;
  }
  .lbm__row {
    font-size: 11px;
  }
  .lbm__btn {
    font-size: 11px;
    height: 36px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .lbm__btn {
    transition: none !important;
  }
}

(function () {
  var list = document.getElementById('lbmList');
  var btn = document.getElementById('lbmBtn');
  var label = document.getElementById('lbmLabel');
  var root = document.getElementById('lbm');

  var BATCH_SIZE = 6;
  var TOTAL = 24;
  var LOAD_DELAY_MS = 560;
  var WIDTH_LERP = 0.24;
  var PADDING_X = 40;

  var remaining = TOTAL;
  var shown = 0;
  var loading = false;
  var done = false;
  var resetting = false;
  var targetWidth = 0;
  var widthRaf = null;
  var autoplayTimer = null;

  function addCard(n) {
    var li = document.createElement('li');
    li.className = 'lbm__row';
    li.textContent = 'Comment ' + String(n).padStart(2, '0');
    list.appendChild(li);
  }
  for (var i = 0; i < 4; i += 1) { shown += 1; addCard(shown); }
  remaining = TOTAL - shown;

  // 계산 겹: 라벨 문자열이 바뀔 때마다 실제 렌더 폭(getBoundingClientRect)을 재고 그 값 + 여백을
  // 목표 너비로 삼아, 매 프레임 현재 너비를 목표 쪽으로 24% 씩 당기는 lerp 로 버튼을 모핑한다.
  function morphTo(text) {
    label.textContent = text;
    var natural = label.getBoundingClientRect().width;
    targetWidth = Math.round(natural + PADDING_X);
    if (widthRaf) { return; }
    var current = btn.getBoundingClientRect().width;
    function tick() {
      current += (targetWidth - current) * WIDTH_LERP;
      btn.style.width = current + 'px';
      if (Math.abs(targetWidth - current) > 0.5) {
        widthRaf = requestAnimationFrame(tick);
      } else {
        btn.style.width = targetWidth + 'px';
        widthRaf = null;
      }
    }
    widthRaf = requestAnimationFrame(tick);
  }

  function labelFor() {
    if (done) { return 'All caught up'; }
    if (loading) { return 'Loading'; }
    return 'Load more (' + remaining + ')';
  }

  function press() {
    if (loading || done) { return; }
    loading = true;
    btn.classList.add('lbm__btn--loading');
    morphTo(labelFor());
    setTimeout(function () {
      var n = Math.min(BATCH_SIZE, remaining);
      for (var k = 0; k < n; k += 1) { shown += 1; addCard(shown); }
      remaining -= n;
      loading = false;
      btn.classList.remove('lbm__btn--loading');
      if (remaining <= 0) {
        done = true;
        btn.classList.add('lbm__btn--done');
        btn.disabled = true;
      }
      morphTo(labelFor());
    }, LOAD_DELAY_MS);
  }

  btn.addEventListener('click', function () {
    root.classList.remove('is-demo');
    stopAutoplay();
    press();
  });

  function stopAutoplay() {
    if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; }
  }

  function autoplayTick() {
    if (done && !resetting) {
      resetting = true;
      setTimeout(function () {
        while (list.firstChild) { list.removeChild(list.firstChild); }
        shown = 0; remaining = TOTAL; done = false; resetting = false;
        btn.disabled = false;
        btn.classList.remove('lbm__btn--done');
        for (var i = 0; i < 4; i += 1) { shown += 1; addCard(shown); }
        remaining = TOTAL - shown;
        morphTo(labelFor());
      }, 700);
      return;
    }
    if (resetting || loading) { return; }
    press();
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  morphTo(labelFor());
  if (!reduce) {
    autoplayTimer = setInterval(autoplayTick, 780);
  }
})();

import { useEffect, useRef, useState, useCallback } from "react";
import styles from "./LoadMoreButtonMorph.module.scss";

// 더 보기 버튼 모핑 — morphTo() 가 라벨의 실측 폭 + 여백을 목표 너비로 삼고,
// 매 프레임 현재 너비를 목표 쪽으로 24% 씩 당기는 lerp(관성)로 버튼 폭을 바꾼다.
const BATCH_SIZE = 6;
const TOTAL = 24;
const LOAD_DELAY_MS = 560;
const WIDTH_LERP = 0.24;
const PADDING_X = 40;

export default function LoadMoreButtonMorph() {
  const rootRef = useRef<HTMLDivElement>(null);
  const btnRef = useRef<HTMLButtonElement>(null);
  const labelRef = useRef<HTMLSpanElement>(null);
  const [rows, setRows] = useState(4);
  const [label, setLabel] = useState("더 보기 (20)");
  const [btnState, setBtnState] = useState<"idle" | "loading" | "done">("idle");
  const rowsRef = useRef(4);
  rowsRef.current = rows;
  const stateRef = useRef<"idle" | "loading" | "done">("idle");
  stateRef.current = btnState;
  const widthRafRef = useRef<number | null>(null);
  const targetWidthRef = useRef<number>(0);
  const autoplayRef = useRef<number | null>(null);

  // 계산 겹: 라벨 문자열이 바뀔 때마다 실제 렌더 폭(getBoundingClientRect)을 재고 그 값 + 여백을
  // 목표 너비로 삼아, 매 프레임 현재 너비를 목표 쪽으로 24% 씩 당기는 lerp 로 버튼을 모핑한다.
  const morphTo = useCallback((text: string) => {
    const btn = btnRef.current;
    const labelEl = labelRef.current;
    if (!btn || !labelEl) { return; }
    labelEl.textContent = text;
    const natural = labelEl.getBoundingClientRect().width;
    targetWidthRef.current = Math.round(natural + PADDING_X);
    if (widthRafRef.current !== null) { return; }
    let current = btn.getBoundingClientRect().width;
    const tick = () => {
      const target = targetWidthRef.current ?? 0;
      current += (target - current) * WIDTH_LERP;
      btn.style.width = current + "px";
      if (Math.abs(target - current) > 0.5) {
        widthRafRef.current = window.requestAnimationFrame(tick);
      } else {
        btn.style.width = target + "px";
        widthRafRef.current = null;
      }
    };
    widthRafRef.current = window.requestAnimationFrame(tick);
  }, []);

  const labelFor = useCallback(() => {
    const shown = rowsRef.current ?? 0;
    const remaining = TOTAL - shown;
    const st = stateRef.current ?? "idle";
    if (st === "done") { return "모두 확인했어요"; }
    if (st === "loading") { return "불러오는 중"; }
    return "더 보기 (" + remaining + ")";
  }, []);

  const press = useCallback(() => {
    if (stateRef.current !== "idle") { return; }
    setBtnState("loading");
    setLabel(labelFor());
    morphTo(labelFor());
    window.setTimeout(() => {
      setRows((prev) => Math.min(prev + BATCH_SIZE, TOTAL));
      const after = Math.min((rowsRef.current ?? 0) + BATCH_SIZE, TOTAL);
      if (after >= TOTAL) {
        setBtnState("done");
      } else {
        setBtnState("idle");
      }
      const shownNow = stateRef.current === "done" ? TOTAL : after;
      const st = shownNow >= TOTAL ? "done" : "idle";
      setLabel(st === "done" ? "모두 확인했어요" : "더 보기 (" + (TOTAL - shownNow) + ")");
      morphTo(st === "done" ? "모두 확인했어요" : "더 보기 (" + (TOTAL - shownNow) + ")");
    }, LOAD_DELAY_MS);
  }, [labelFor, morphTo]);

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) {
      autoplayRef.current = window.setInterval(() => {
        press();
      }, 780);
    }
    return () => {
      if (autoplayRef.current !== null) { window.clearInterval(autoplayRef.current); }
      if (widthRafRef.current !== null) { window.cancelAnimationFrame(widthRafRef.current); }
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  const rowEls = [];
  for (let i = 0; i < rows; i += 1) {
    rowEls.push(
      <li key={i} className={styles["lbm__row"]}>댓글 {String(i + 1).padStart(2, "0")}</li>
    );
  }

  return (
    <main className={styles.stage}>
      <div ref={rootRef} className={`${styles.lbm} ${styles["is-demo"]}`} id="lbm">
        <ul className={styles["lbm__list"]}>{rowEls}</ul>
        <button
          ref={btnRef}
          className={`${styles["lbm__btn"]} ${btnState === "loading" ? styles["lbm__btn--loading"] : ""} ${btnState === "done" ? styles["lbm__btn--done"] : ""}`}
          type="button"
          disabled={btnState === "done"}
          onClick={() => {
            rootRef.current?.classList.remove(styles["is-demo"]);
            if (autoplayRef.current !== null) { window.clearInterval(autoplayRef.current); }
            press();
          }}
        >
          <span ref={labelRef} className={styles["lbm__label"]}>{label}</span>
        </button>
      </div>
    </main>
  );
}