import styleText from './my-element.css.js'; const stylesheet = new CSSStyleSheet(); //stylesheet.replaceSync(styleText); export default class extends HTMLElement { constructor() { super(); this.shadow = this.attachShadow({ mode: 'open' }); this.shadow.adoptedStyleSheets = [stylesheet]; } // カスタム要素がDOMに追加された後 connectedCallback() { console.log('connectedCallback()'); if (stylesheet.cssRules.length == 0) { console.log('stylesheet.replaceSync(styleText)'); stylesheet.replaceSync(styleText); } this.shadow.innerHTML = `
Hello, World!
`; } }