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class CustomSquare extends HTMLElement {
  constructor() {

    this.shadow = this.attachShadow({ mode: 'open' });

    const div = document.createElement('div');
    console.log('Create Custom square element')

  // DOM에 추가
  connectedCallback() {
    console.log('Custom square element added to page', this.parentElement.tagName);

  // DOM에서 제거
  disconnectedCallback() {
    console.log('Custom square element removed from page', 'isConnected:', this.isConnected);

  // DOM 이동
  adoptedCallback() {
    console.log('Custom square element moved to new page', this.parentElement.tagName);

  // 애트리뷰트 변경
  attributeChangedCallback(name, oldValue, newValue) {
    console.log('Custom square element attributes changed', name);

  static get observedAttributes() {
    // 애트리뷰트 이름을 담은 배열을 반환
    return ['c', 'l']; // 'c'와 'l' 애트리뷰트 변경을 감지
customElements.define('custom-square', CustomSquare);

// 엘리먼트 생성
// - Create Custom square element
const cs = document.createElement('custom-square');

// 엘리먼트 추가
// - "Custom square element added to page" "HEAD"

// 엘리먼트 이동
// - "Custom square element removed from page" "isConnected:" true
// - "Custom square element added to page" "BODY"

// 애트리뷰트 변경
// - "Custom square element attributes changed" "l"
cs.setAttribute('l', '2');

// 애트리뷰트 변경 (console에 나타나지 않음)
cs.setAttribute('no', '3');

// 엘리먼트 제거
// - "Custom square element removed from page" "isConnected:" false