Source Code: (back to article)
<div id="interactive-host"></div>

<script>
const interactiveHost = document.getElementById('interactive-host');
const shadowRoot = interactiveHost.attachShadow({ mode: 'open' });

shadowRoot.innerHTML = `
<button id="shadow-btn">Click me</button>
`;

const shadowButton = shadowRoot.getElementById('shadow-btn');
shadowButton.addEventListener('click', () => {
alert('Button inside Shadow DOM clicked!');
});
</script>