The following snippets are taken from our slotted-pseudo-element demo (see it live also).
In this demo we use a simple template with three slots:
<template id="person-template">
<div>
<h2>Personal ID Card</h2>
<slot name="person-name">NAME MISSING</slot>
<ul>
<li><slot name="person-age">AGE MISSING</slot></li>
<li><slot name="person-occupation">OCCUPATION MISSING</slot></li>
</ul>
</div>
</template>
A custom element — <person-details> — is defined like so:
customElements.define('person-details',
class extends HTMLElement {
constructor() {
super();
let template = document.getElementById('person-template');
let templateContent = template.content;
const shadowRoot = this.attachShadow({mode: 'open'});
let style = document.createElement('style');
style.textContent = 'div { padding: 10px; border: 1px solid gray; width: 200px; margin: 10px; }' +
'h2 { margin: 0 0 10px; }' +
'ul { margin: 0; }' +
'p { margin: 10px 0; }' +
'::slotted(*) { color: gray; font-family: sans-serif; } ';
shadowRoot.appendChild(style);
shadowRoot.appendChild(templateContent.cloneNode(true));
}
})
You'll see that when filling the style element with content, we select all slotted elements (::slotted(*)) and give them a different font and color. This allows them to stand out better next to the slots that haven't been successfully filled.
The element looks like this when inserted into the page:
<person-details>
<p slot="person-name">Dr. Shazaam</p>
<span slot="person-age">Immortal</span>
<span slot="person-occupation">Superhero</span>
</person-details>