01라벨이 스피너 아이콘으로 자연스럽게 바뀌는 버튼

<main class="stage">
<div class="scene is-demo" id="scene">
  <button class="btn" id="btn" type="button">
    <span class="btnContent" id="content">
      <span class="btnLabel" id="label">Save changes</span>
      <span class="btnSpinner" id="spinnerWrap" aria-hidden="true"><span class="btnRing" id="ring"></span></span>
    </span>
  </button>
  <span class="visuallyHidden" id="status" role="status" aria-live="polite"></span>
</div>
</main>

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

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

// 계산 겹: index.html 의 lockWidth() 가 라벨이 보이는 순간의 버튼 실측 폭을 px 로 고정하고,
// spinLoop() 가 매 프레임 각도를 산술로 계산해 style.transform 에 적어 넣는다(트랜지션이 아니다).
@include stage($stage-ink);

.scene {
  display: grid;
  place-items: center;
}

.btn {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 44px;
  padding: 0 $sp-5;
  border: none;
  border-radius: $r-control;
  background: $color;
  color: $subject-cream;
  font-weight: 600;
  font-size: 14px;
  line-height: 1;
  box-shadow: $shadow-press;
  cursor: pointer;
  transition: box-shadow $duration $easing;

  &:focus-visible { outline: 2px solid $subject-cream; outline-offset: 3px; }
  &:disabled { cursor: default; }
  &:active:not(:disabled) { box-shadow: none; }
}

.btnContent {
  position: relative;
  display: inline-block;
  min-width: 84px;
  height: 18px;
}

.btnLabel,
.btnSpinner {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  white-space: nowrap;
}

.btnSpinner { opacity: 0; }

.btnRing {
  width: 16px;
  height: 16px;
  border-radius: $r-pill;
  border: 2px solid rgba($subject-cream, .28);
  border-top-color: $subject-cream;
}

.visuallyHidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .btn { height: 40px; padding: 0 $sp-4; font-size: 13px; }
  .btnContent { min-width: 72px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용 — index.html 의 runReduced() 가 회전 트윈 없이 opacity 만 즉시 바꾼다.
  // scss 만: 남은 트랜지션을 전부 끈다.
  * { 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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.scene {
  display: grid;
  place-items: center;
}

.btn {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 44px;
  padding: 0 20px;
  border: none;
  border-radius: 12px;
  background: #0a4fe8;
  color: #fff7e6;
  font-weight: 600;
  font-size: 14px;
  line-height: 1;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  cursor: pointer;
  transition: box-shadow 300ms ease-out;
}
.btn:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 3px;
}
.btn:disabled {
  cursor: default;
}
.btn:active:not(:disabled) {
  box-shadow: none;
}

.btnContent {
  position: relative;
  display: inline-block;
  min-width: 84px;
  height: 18px;
}

.btnLabel,
.btnSpinner {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  white-space: nowrap;
}

.btnSpinner {
  opacity: 0;
}

.btnRing {
  width: 16px;
  height: 16px;
  border-radius: 999px;
  border: 2px solid rgba(255, 247, 230, 0.28);
  border-top-color: #fff7e6;
}

.visuallyHidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .btn {
    height: 40px;
    padding: 0 16px;
    font-size: 13px;
  }
  .btnContent {
    min-width: 72px;
  }
}
@media (prefers-reduced-motion: reduce) {
  * {
    transition: none !important;
  }
}

(function () {
  var FADE_MS = 180;
  var SPIN_MS = 900;
  var GAP_MS = 500;
  var START_DELAY_MS = 200;
  var DEG_PER_MS = 360 / 650;

  var scene = document.getElementById('scene');
  var btn = document.getElementById('btn');
  var label = document.getElementById('label');
  var spinnerWrap = document.getElementById('spinnerWrap');
  var ring = document.getElementById('ring');
  var status = document.getElementById('status');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var gen = 0;
  var timers = [];
  var rafId = 0;

  function human() {
    if (scene.classList.contains('is-demo')) {
      scene.classList.remove('is-demo');
      timers.forEach(function (t) { clearTimeout(t); });
      timers = [];
    }
  }

  function easeInOutQuad(p) { return p < .5 ? 2 * p * p : 1 - Math.pow(-2 * p + 2, 2) / 2; }

  function fade(el, from, to, ms, myGen, onDone) {
    var start = null;
    function step(now) {
      if (myGen !== gen) return;
      if (start === null) start = now;
      var p = Math.min(1, (now - start) / ms);
      el.style.opacity = String(from + (to - from) * easeInOutQuad(p));
      if (p < 1) requestAnimationFrame(step); else if (onDone) onDone();
    }
    requestAnimationFrame(step);
  }

  function spinLoop(myGen) {
    var start = null;
    function step(now) {
      if (myGen !== gen) return;
      if (start === null) start = now;
      var angle = ((now - start) * DEG_PER_MS) % 360;
      ring.style.transform = 'rotate(' + angle.toFixed(1) + 'deg)';
      rafId = requestAnimationFrame(step);
    }
    rafId = requestAnimationFrame(step);
  }

  // 계산 겹: 라벨이 보이는 지금 이 순간의 버튼 실측 폭을 lockWidth() 가 px 로 고정한다 —
  // 스피너로 바뀌며 콘텐츠 폭이 좁아져도 버튼이 함께 좁아지지 않는다.
  function lockWidth() {
    var w = btn.getBoundingClientRect().width;
    btn.style.width = w + 'px';
  }
  function unlockWidth() { btn.style.width = ''; }

  function startLoad(myGen) {
    lockWidth();
    btn.disabled = true;
    btn.setAttribute('aria-busy', 'true');
    status.textContent = '저장하는 중';
    fade(label, 1, 0, FADE_MS, myGen);
    fade(spinnerWrap, 0, 1, FADE_MS, myGen, function () { spinLoop(myGen); });
  }
  function finishLoad(myGen) {
    cancelAnimationFrame(rafId);
    fade(spinnerWrap, 1, 0, FADE_MS, myGen);
    fade(label, 0, 1, FADE_MS, myGen, function () {
      btn.disabled = false;
      btn.removeAttribute('aria-busy');
      status.textContent = '저장 완료';
      unlockWidth();
    });
  }

  function runAnimated() {
    gen++;
    var myGen = gen;
    startLoad(myGen);
    timers.push(setTimeout(function () { finishLoad(myGen); }, SPIN_MS));
  }

  function runReduced() {
    gen++;
    lockWidth();
    btn.disabled = true;
    btn.setAttribute('aria-busy', 'true');
    status.textContent = '저장하는 중';
    label.style.opacity = '0';
    spinnerWrap.style.opacity = '1';
    timers.push(setTimeout(function () {
      spinnerWrap.style.opacity = '0';
      label.style.opacity = '1';
      btn.disabled = false;
      btn.removeAttribute('aria-busy');
      status.textContent = '저장 완료';
      unlockWidth();
    }, SPIN_MS));
  }

  btn.addEventListener('click', function () {
    if (btn.disabled) return;
    human();
    if (reduce) runReduced(); else runAnimated();
  });

  // reduce: 실사용 경로 적용 — runReduced() 는 회전 트윈 없이 opacity 만 즉시 바꾼다.
  // 아래 자동 루프는 시연 게이트만 — reduce 에서는 돌지 않는다.
  function cycle() {
    if (!scene.classList.contains('is-demo')) return;
    runAnimated();
    timers.push(setTimeout(function () {
      timers.push(setTimeout(cycle, GAP_MS));
    }, SPIN_MS));
  }

  if (!reduce) {
    timers.push(setTimeout(cycle, START_DELAY_MS));
  }
})();

import { useEffect, useRef } from 'react';
import styles from './ButtonLoadingSpinnerSwap.module.scss';

const FADE_MS = 180;
const SPIN_MS = 900;
const GAP_MS = 500;
const START_DELAY_MS = 200;
const DEG_PER_MS = 360 / 650;

export default function ButtonLoadingSpinnerSwap() {
  const sceneRef = useRef<HTMLDivElement>(null);
  const btnRef = useRef<HTMLButtonElement>(null);
  const labelRef = useRef<HTMLSpanElement>(null);
  const spinnerWrapRef = useRef<HTMLSpanElement>(null);
  const ringRef = useRef<HTMLSpanElement>(null);
  const statusRef = useRef<HTMLSpanElement>(null);

  useEffect(() => {
    const scene = sceneRef.current;
    const btn = btnRef.current;
    const label = labelRef.current;
    const spinnerWrap = spinnerWrapRef.current;
    const ring = ringRef.current;
    const status = statusRef.current;
    if (!scene || !btn || !label || !spinnerWrap || !ring || !status) return undefined;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    let gen = 0;
    let timers: number[] = [];
    let rafId = 0;

    function human() {
      if (scene!.classList.contains(styles['is-demo'])) {
        scene!.classList.remove(styles['is-demo']);
        timers.forEach((t) => window.clearTimeout(t));
        timers = [];
      }
    }

    function easeInOutQuad(p: number) { return p < .5 ? 2 * p * p : 1 - Math.pow(-2 * p + 2, 2) / 2; }

    function fade(el: HTMLElement, from: number, to: number, ms: number, myGen: number, onDone?: () => void) {
      let start: number | null = null;
      function step(now: number) {
        if (myGen !== gen) return;
        if (start === null) start = now;
        const p = Math.min(1, (now - start) / ms);
        el.style.opacity = String(from + (to - from) * easeInOutQuad(p));
        if (p < 1) requestAnimationFrame(step); else if (onDone) onDone();
      }
      requestAnimationFrame(step);
    }

    function spinLoop(myGen: number) {
      let start: number | null = null;
      function step(now: number) {
        if (myGen !== gen) return;
        if (start === null) start = now;
        const angle = ((now - start) * DEG_PER_MS) % 360;
        ring!.style.transform = 'rotate(' + angle.toFixed(1) + 'deg)';
        rafId = requestAnimationFrame(step);
      }
      rafId = requestAnimationFrame(step);
    }

    // 계산 겹: 라벨이 보이는 지금 이 순간의 버튼 실측 폭을 lockWidth() 가 px 로 고정한다 —
    // 스피너로 바뀌며 콘텐츠 폭이 좁아져도 버튼이 함께 좁아지지 않는다.
    function lockWidth() {
      const w = btn!.getBoundingClientRect().width;
      btn!.style.width = w + 'px';
    }
    function unlockWidth() { btn!.style.width = ''; }

    function startLoad(myGen: number) {
      lockWidth();
      btn!.disabled = true;
      btn!.setAttribute('aria-busy', 'true');
      status!.textContent = '저장하는 중';
      fade(label!, 1, 0, FADE_MS, myGen);
      fade(spinnerWrap!, 0, 1, FADE_MS, myGen, () => { spinLoop(myGen); });
    }
    function finishLoad(myGen: number) {
      cancelAnimationFrame(rafId);
      fade(spinnerWrap!, 1, 0, FADE_MS, myGen);
      fade(label!, 0, 1, FADE_MS, myGen, () => {
        btn!.disabled = false;
        btn!.removeAttribute('aria-busy');
        status!.textContent = '저장 완료';
        unlockWidth();
      });
    }

    function runAnimated() {
      gen++;
      const myGen = gen;
      startLoad(myGen);
      timers.push(window.setTimeout(() => { finishLoad(myGen); }, SPIN_MS));
    }

    function runReduced() {
      gen++;
      lockWidth();
      btn!.disabled = true;
      btn!.setAttribute('aria-busy', 'true');
      status!.textContent = '저장하는 중';
      label!.style.opacity = '0';
      spinnerWrap!.style.opacity = '1';
      timers.push(window.setTimeout(() => {
        spinnerWrap!.style.opacity = '0';
        label!.style.opacity = '1';
        btn!.disabled = false;
        btn!.removeAttribute('aria-busy');
        status!.textContent = '저장 완료';
        unlockWidth();
      }, SPIN_MS));
    }

    function onClick() {
      if (btn!.disabled) return;
      human();
      if (reduce) runReduced(); else runAnimated();
    }
    btn.addEventListener('click', onClick);

    // reduce: 실사용 경로 적용 — runReduced() 는 회전 트윈 없이 opacity 만 즉시 바꾼다.
    // 아래 자동 루프는 시연 게이트만 — reduce 에서는 돌지 않는다.
    function cycle() {
      if (!scene!.classList.contains(styles['is-demo'])) return;
      runAnimated();
      timers.push(window.setTimeout(() => {
        timers.push(window.setTimeout(cycle, GAP_MS));
      }, SPIN_MS));
    }

    if (!reduce) {
      timers.push(window.setTimeout(cycle, START_DELAY_MS));
    }

    return () => {
      btn.removeEventListener('click', onClick);
      timers.forEach((t) => window.clearTimeout(t));
      cancelAnimationFrame(rafId);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.scene + ' ' + styles['is-demo']} ref={sceneRef}>
        <button className={styles.btn} ref={btnRef} type="button">
          <span className={styles.btnContent}>
            <span className={styles.btnLabel} ref={labelRef}>Save changes</span>
            <span className={styles.btnSpinner} ref={spinnerWrapRef} aria-hidden="true">
              <span className={styles.btnRing} ref={ringRef} />
            </span>
          </span>
        </button>
        <span className={styles.visuallyHidden} ref={statusRef} role="status" aria-live="polite" />
      </div>
    </main>
  );
}