Web Component Example: Just Some HTML

customElements.define('wc-widget', 
    class Widget extends HTMLElement {
        constructor() {
            super()
            this.attachShadow({ mode: 'open' })
            this.content = document.createElement('div')
            this.content.innerHTML = 'This is a web component'
            this.shadowRoot.append(this.content)
        }
    }
)