JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://getfirebug.com/firebug-lite-debug.js"></script>
<script>
window.customElements.define('elmt-container', class extends HTMLElement {
    connectedCallback() {
    		console.log("container connected");
        console.log(this.children.length);
    }
});
window.customElements.define('elmt-test', class extends HTMLElement { });
</script>


<elmt-container>
        <div>1</div>
        <elmt-test>2</elmt-test>
</elmt-container>