08保存したカーソル位置の値に正確に挿入する挿入方式

<main class="stage">
<div class="ip is-demo" id="ip">
  <textarea class="ip__field" id="ipField" rows="3" aria-label="メッセージ入力"></textarea>
  <div class="ip__panel" role="group" aria-label="絵文字挿入">
    <button class="ip__pick" type="button" aria-label="星">&#11088;</button>
    <button class="ip__pick" type="button" aria-label="風船">&#127880;</button>
    <button class="ip__pick" type="button" aria-label="画鋲">&#128204;</button>
    <button class="ip__pick" type="button" aria-label="四つ葉のクローバー">&#127808;</button>
  </div>
  <p class="ip__sr" role="status" aria-live="polite" id="ipLive"></p>
</div>
</main>

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

// 계산 겹: index.html 이 blur 시각의 selectionStart/selectionEnd 값을 저장해 두고,
// 이모지를 고르면 그 값이 가리키던 글자 사이로 되돌아가 끼워 넣는다 — 끝에 붙이지 않는다.
@include stage($stage-paper);

.ip { display: flex; flex-direction: column; align-items: center; gap: $sp-3; width: 100%; padding: 0 $sp-3; }

.ip__field {
  width: 100%; max-width: 300px; min-height: 64px; border: none; border-radius: $r-control;
  background: rgba($subject-ink, .06); color: $subject-ink; font-size: 13px; line-height: 1.6;
  padding: $sp-2; resize: none; box-shadow: 0 0 0 1px rgba($subject-ink, .12) inset;
  font-family: inherit;
}
.ip__field:focus-visible { outline: 2px solid $subject-blue; outline-offset: 2px; }

.ip__panel { display: flex; gap: $sp-2; }
.ip__pick {
  width: 34px; height: 34px; border: none; border-radius: $r-sm; background: rgba($subject-blue, .14);
  font-size: 17px; cursor: pointer; display: flex; align-items: center; justify-content: center;
  transform: scale(1); transition: transform $dur-quick $ease-spring, background $dur-quick $ease-out;
}
.ip__pick:hover, .ip__pick:focus-visible { background: rgba($subject-blue, .26); transform: scale(1.12); }
.ip__pick--pop { animation: ipPop $dur-quick $ease-pop; }

.ip__sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); margin: -1px; padding: 0; border: 0; }

@keyframes ipPop {
  0% { transform: scale(.7); }
  60% { transform: scale(1.22); }
  100% { transform: scale(1); }
}

@media (max-width: 340px) {
  .ip__field { max-width: 260px; min-height: 56px; font-size: 12px; }
  .ip__pick { width: 28px; height: 28px; font-size: 14px; }
}

@media (prefers-reduced-motion: reduce) {
  .ip__pick { transition: none; }
  .ip__pick--pop { animation: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ip {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: 100%;
  padding: 0 12px;
}

.ip__field {
  width: 100%;
  max-width: 300px;
  min-height: 64px;
  border: none;
  border-radius: 12px;
  background: rgba(23, 20, 26, 0.06);
  color: #17141a;
  font-size: 13px;
  line-height: 1.6;
  padding: 8px;
  resize: none;
  box-shadow: 0 0 0 1px rgba(23, 20, 26, 0.12) inset;
  font-family: inherit;
}

.ip__field:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}

.ip__panel {
  display: flex;
  gap: 8px;
}

.ip__pick {
  width: 34px;
  height: 34px;
  border: none;
  border-radius: 8px;
  background: rgba(47, 109, 246, 0.14);
  font-size: 17px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transform: scale(1);
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1), background 220ms ease-out;
}

.ip__pick:hover, .ip__pick:focus-visible {
  background: rgba(47, 109, 246, 0.26);
  transform: scale(1.12);
}

.ip__pick--pop {
  animation: ipPop 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.ip__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  margin: -1px;
  padding: 0;
  border: 0;
}

@keyframes ipPop {
  0% {
    transform: scale(0.7);
  }
  60% {
    transform: scale(1.22);
  }
  100% {
    transform: scale(1);
  }
}
@media (max-width: 340px) {
  .ip__field {
    max-width: 260px;
    min-height: 56px;
    font-size: 12px;
  }
  .ip__pick {
    width: 28px;
    height: 28px;
    font-size: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ip__pick {
    transition: none;
  }
  .ip__pick--pop {
    animation: none;
  }
}

(function () {
  var root = document.getElementById('ip');
  var field = document.getElementById('ipField');
  var live = document.getElementById('ipLive');
  var synthetic = false;
  function human() { if (synthetic) return; if (root.classList.contains('is-demo')) root.classList.remove('is-demo'); }

  // 계산 겹: 입력창이 초점을 잃기 직전(blur)에 selectionStart/selectionEnd 값을 저장해 두고,
  // 이모지를 고르는 순간 그 값이 가리키던 文字 사이에 정확히 끼워 넣어 커서를 그 자리로 되돌린다.
  // (끝에 이어붙이면 값을 안 쓴 것과 같다 — 저장된 위치 값을 실제로 읽어 쓰는 것이 계산 겹이다.)
  var savedStart = 0;
  var savedEnd = 0;
  field.addEventListener('blur', function () {
    savedStart = field.selectionStart;
    savedEnd = field.selectionEnd;
  });

  field.addEventListener('input', function () {
    live.textContent = '文字 ' + field.value.length + '個、カーソル ' + field.selectionStart + '番目';
  });

  var picks = Array.prototype.slice.call(document.querySelectorAll('.ip__pick'));
  picks.forEach(function (btn) {
    btn.addEventListener('click', function () {
      human();
      var emoji = btn.textContent;
      var value = field.value;
      var before = value.slice(0, savedStart);
      var after = value.slice(savedEnd);
      field.value = before + emoji + after;
      var landAt = savedStart + emoji.length;
      field.focus({ preventScroll: true });
      field.setSelectionRange(landAt, landAt);
      savedStart = landAt;
      savedEnd = landAt;
      live.textContent = before.length + '文字目の後ろに挿入、カーソル ' + landAt + '番目へ移動';
      btn.classList.add('ip__pick--pop');
      window.setTimeout(function () { btn.classList.remove('ip__pick--pop'); }, 260);
    });
  });

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var DEMO_TEXT = 'お昼ご飯本当に美味しかった';
  var MID = 5;
  var step = 0, loopTimer = 0;
  function runStep() {
    if (!root.classList.contains('is-demo')) return;
    synthetic = true;
    if (step % 2 === 0) {
      field.value = DEMO_TEXT;
      field.focus({ preventScroll: true });
      field.setSelectionRange(MID, MID);
      field.blur();
    } else {
      var idx = (step / 2) % picks.length | 0;
      picks[idx].dispatchEvent(new MouseEvent('click', { bubbles: true }));
    }
    synthetic = false;
    step++;
    loopTimer = window.setTimeout(runStep, 620);
  }
  if (!reduce) { loopTimer = window.setTimeout(runStep, 480); }
  else { root.classList.remove('is-demo'); }
})();

// EmojiPickerInsertCursorPositionPreserve — vanilla 판(run/402/demo/08-.../index.html) 의 React 포트.
// 계산 겹: 입력창이 blur 되는 순간의 selectionStart/selectionEnd 값을 저장해 두고, 이모지를
// 고르면 그 값이 가리키던 글자 사이로 되돌아가 끼워 넣는다 — 끝에 이어붙이지 않는다.
import { useEffect, useRef, useState } from "react";
import styles from "./EmojiPickerInsertCursorPositionPreserve.module.scss";

type Box<T> = { current: T };

const PICKS = [
  { ch: "⭐", label: "별" },
  { ch: "\u{1F388}", label: "풍선" },
  { ch: "\u{1F4CC}", label: "압정" },
  { ch: "\u{1F340}", label: "네잎클로버" },
];

const DEMO_TEXT = "점심 진짜 맛있었어";
const MID = 5;

export default function EmojiPickerInsertCursorPositionPreserve() {
  const [isDemo, setIsDemo] = useState(true);
  const [value, setValue] = useState("");
  const [live, setLive] = useState("");
  const [popIndex, setPopIndex] = useState(-1);

  const isDemoRef = useRef(true) as unknown as Box<boolean>;
  const synthRef = useRef(false) as unknown as Box<boolean>;
  const valueRef = useRef("") as unknown as Box<string>;
  const savedStartRef = useRef(0) as unknown as Box<number>;
  const savedEndRef = useRef(0) as unknown as Box<number>;
  const fieldRef = useRef(null) as unknown as Box<HTMLTextAreaElement>;
  const loopTimerRef = useRef(0) as unknown as Box<number>;
  const popTimerRef = useRef(0) as unknown as Box<number>;

  function human() {
    if (synthRef.current) return;
    if (isDemoRef.current) { isDemoRef.current = false; setIsDemo(false); }
  }

  function onBlur() {
    const el = fieldRef.current;
    if (!el) return;
    savedStartRef.current = el.selectionStart;
    savedEndRef.current = el.selectionEnd;
  }

  function onInput(e: { target: { value: string; selectionStart: number | null } }) {
    valueRef.current = e.target.value;
    setValue(e.target.value);
    setLive("글자 " + e.target.value.length + "개, 커서 " + (e.target.selectionStart ?? 0) + "번째");
  }

  function pick(i: number) {
    human();
    const emoji = PICKS[i].ch;
    const start = savedStartRef.current;
    const end = savedEndRef.current;
    const cur = valueRef.current;
    const before = cur.slice(0, start);
    const after = cur.slice(end);
    const next = before + emoji + after;
    valueRef.current = next;
    setValue(next);
    const landAt = start + emoji.length;
    savedStartRef.current = landAt;
    savedEndRef.current = landAt;
    setLive(before.length + "번째 글자 뒤에 끼워짐, 커서 " + landAt + "번째로 이동");
    const el = fieldRef.current;
    if (el) {
      window.setTimeout(() => {
        el.focus({ preventScroll: true });
        el.setSelectionRange(landAt, landAt);
      }, 0);
    }
    setPopIndex(i);
    window.clearTimeout(popTimerRef.current);
    popTimerRef.current = window.setTimeout(() => setPopIndex(-1), 260);
  }

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let step = 0;
    function runStep() {
      if (!isDemoRef.current) return;
      synthRef.current = true;
      if (step % 2 === 0) {
        valueRef.current = DEMO_TEXT;
        setValue(DEMO_TEXT);
        const el = fieldRef.current;
        if (el) {
          el.focus({ preventScroll: true });
          el.setSelectionRange(MID, MID);
          el.blur();
        } else {
          savedStartRef.current = MID;
          savedEndRef.current = MID;
        }
      } else {
        const idx = Math.floor(step / 2) % PICKS.length;
        pick(idx);
      }
      synthRef.current = false;
      step++;
      loopTimerRef.current = window.setTimeout(runStep, 620);
    }
    if (!reduce) { loopTimerRef.current = window.setTimeout(runStep, 480); }
    else { isDemoRef.current = false; setIsDemo(false); }
    return () => { window.clearTimeout(loopTimerRef.current); window.clearTimeout(popTimerRef.current); };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.ip + " " + (isDemo ? styles.isDemo : "")}>
        <textarea
          className={styles.field}
          rows={3}
          aria-label="메시지 입력"
          ref={fieldRef}
          value={value}
          onChange={onInput}
          onBlur={onBlur}
        />
        <div className={styles.panel} role="group" aria-label="이모지 삽입">
          {PICKS.map((p, i) => (
            <button
              key={i}
              type="button"
              className={styles.pick + " " + (popIndex === i ? styles.pickPop : "")}
              aria-label={p.label}
              onClick={() => pick(i)}
            >
              {p.ch}
            </button>
          ))}
        </div>
        <p className={styles.sr} role="status" aria-live="polite">{live}</p>
      </div>
    </main>
  );
}