08Đếm số ký tự

<main class="stage">
  <div class="cc is-demo">
    <label class="cc__label" for="cc-bio">Tiểu sử</label>
    <textarea id="cc-bio" class="cc__input" maxlength="40" placeholder="Giới thiệu ngắn (tối đa 40 ký tự)" rows="2"></textarea>
    <span class="cc__count" aria-live="polite"><b class="cc__num">0</b>/40</span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-instant;               // 숫자가 튕기는 시간
$easing: $ease-pop;
$color: $subject-blue;                 // 숫자·포커스 색

// ── 스프링 감쇠 반동 계수 ────────────────────────────────
// 진폭이 매 반동마다 γ=.42 배로 줄어든다 — 1 기준 진폭 .35 → -.147 → +.062
$b1: 1.35;              // 첫 최대 진폭 (진폭 +.35)
$b2: 1 - .35 * .42;     // 1회 반동(반대 방향, 진폭 -.147) → .853
$b3: 1 + .35 * .42 * .42; // 2회 반동(제자리 방향, 진폭 +.062) → 1.062

@include stage($stage-paper);

.cc { width: min(240px, 82vw); }
.cc__label { display: block; margin-bottom: $sp-2; font-weight: 700; font-size: 13px; line-height: 1; font-family: inherit; color: rgba($stage-ink, .75); }
.cc__input {
  box-sizing: border-box;
  width: 100%;
  resize: none;
  border: 2px solid rgba($stage-ink, .2);
  border-radius: $r-control;
  padding: $sp-3 $sp-3;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 14px);
  line-height: 1.4;
  font-family: inherit;
  color: $stage-ink;
  background: $subject-cream;

  &:focus { outline: none; border-color: $color; }
}
.cc__count {
  display: block;
  margin-top: $sp-2;
  text-align: right;
  font-weight: 600;
  font-size: 12px;
  line-height: 1;
  font-family: inherit;
  color: rgba($stage-ink, .72);        // 흐린 글자 알파 하한 .72 — 흰 면 위 7.27:1
}
.cc__num { color: $color; display: inline-block; transform: scale(1); }
.cc__count.is-bump .cc__num { animation: bump $duration $easing; }

@keyframes bump {
  // 스프링 오버슛 — 튕긴 뒤 반대 방향 반동 2번을 거쳐 멎는다 (감쇠 진폭 1.35 → .853 → 1.062 → 1)
  0%   { transform: scale(1); }
  35%  { transform: scale(#{$b1}); }
  60%  { transform: scale(1); }
  78%  { transform: scale(#{$b2}); }
  90%  { transform: scale(#{$b3}); }
  100% { transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .cc__count.is-bump .cc__num { 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);
}

.cc {
  width: min(240px, 82vw);
}

.cc__label {
  display: block;
  margin-bottom: 8px;
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  font-family: inherit;
  color: rgba(23, 20, 26, 0.75);
}

.cc__input {
  box-sizing: border-box;
  width: 100%;
  resize: none;
  border: 2px solid rgba(23, 20, 26, 0.2);
  border-radius: 12px;
  padding: 12px 12px;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 14px);
  line-height: 1.4;
  font-family: inherit;
  color: #17141a;
  background: #fff7e6;
}
.cc__input:focus {
  outline: none;
  border-color: #2f6df6;
}

.cc__count {
  display: block;
  margin-top: 8px;
  text-align: right;
  font-weight: 600;
  font-size: 12px;
  line-height: 1;
  font-family: inherit;
  color: rgba(23, 20, 26, 0.72);
}

.cc__num {
  color: #2f6df6;
  display: inline-block;
  transform: scale(1);
}

.cc__count.is-bump .cc__num {
  animation: bump 140ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

@keyframes bump {
  0% {
    transform: scale(1);
  }
  35% {
    transform: scale(1.35);
  }
  60% {
    transform: scale(1);
  }
  78% {
    transform: scale(0.853);
  }
  90% {
    transform: scale(1.06174);
  }
  100% {
    transform: scale(1);
  }
}
@media (prefers-reduced-motion: reduce) {
  .cc__count.is-bump .cc__num {
    animation: none;
  }
}

// 실사용: 입력할 때마다 남은 글자 수를 세고 튕긴다. 데모(.is-demo)는 값을 흉내내 반복 (9줄)
var ta = document.querySelector('.is-demo .cc__input');
var num = document.querySelector('.is-demo .cc__num');
var texts = ['', 'Xin chào', 'Xin chào, tôi là dev'];
var i = 0;
var t = function () {
  ta.value = texts[i % texts.length]; i += 1;
  num.textContent = String(ta.value.length);
  num.parentElement.classList.remove('is-bump'); void num.offsetWidth; num.parentElement.classList.add('is-bump');
};
t(); setInterval(t, 450);

import { useState } from "react";
import type { CSSProperties, ChangeEvent } from "react";
import styles from "./CharCount.module.scss";

export type CharCountProps = {
  id?: string;
  label?: string;
  placeholder?: string;
  maxLength?: number;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function CharCount({
  id = "cc-bio",
  label = "Bio",
  placeholder = "Write a short bio (40 characters max)",
  maxLength = 40,
  duration = 140,
  easing = "cubic-bezier(.2,1.4,.4,1)",
  color = "#2f6df6",
}: CharCountProps) {
  const [value, setValue] = useState("");
  const [bump, setBump] = useState(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  const onChange = (e: ChangeEvent<HTMLTextAreaElement>) => {
    setValue(e.target.value);
    setBump(false);
    requestAnimationFrame(() => setBump(true));
  };

  return (
    <div className={styles.cc} style={vars}>
      <label htmlFor={id} className={styles.label}>{label}</label>
      <textarea
        id={id}
        className={styles.input}
        maxLength={maxLength}
        placeholder={placeholder}
        rows={2}
        value={value}
        onChange={onChange}
      />
      <span className={styles.count} aria-live="polite">
        <b className={bump ? `${styles.num} ${styles.bump}` : styles.num} onAnimationEnd={() => setBump(false)}>
          {value.length}
        </b>
        /{maxLength}
      </span>
    </div>
  );
}