When working with a large amount of content that lives whithin an overlay, a page may encounter performance issues for placing a large amount of content within <sp-overlay> or <overlay-trigger> elements. To avoid this, an empty <sp-overlay> could be used instead. When triggered, the <sp-overlay> element will dispatch slottable-request just before it begins to open and just after it finished closing. When handling these events the contents of an overlay can be lazily rendered into the <sp-overlay> element as it opens and then, as needed, removed from the DOM once the overlay has closed.

yarn add @spectrum-web-components/overlay

Import the side effectful registration of <sp-overlay> as follows:

import '@spectrum-web-components/overlay/sp-overlay.js';

Import type information about the slottable-request event and a symbol to signify that the request is for the DOM to be removed:

import {
    removeSlottableRequest,
    SlottableRequestEvent,
} from '@spectrum-web-components/overlay/src/slottable-request-event.js';

When leveraging the <sp-overlay> in a javascript only context, you can leverage the slottable-request event and its data property to decide whether and what to render into the <sp-overlay> event.

<sp-button id="js-trigger">Trigger</sp-button>
<sp-overlay trigger="js-trigger@click" placement="right-start"></sp-overlay>

<script type="module">
    import { removeSlottableRequest } from '@spectrum-web-components/overlay/src/slottable-request-event.js';

    function initOverlay() {
        const overlay = document.querySelector('[trigger="js-trigger@click"]');
        overlay.addEventListener('slottable-request', function (event) {
            if (event.data === removeSlottableRequest) {
                this.innerHTML = '';
            } else {
                this.innerHTML = `
                <sp-popover>
                    <p>This content will display within the Overlay and <em>only</em> be on the DOM when the Overlay is open.</p>
                </sp-popover>
                `;
            }
        });
    }

    customElements.whenDefined('code-example').then(() => {
        customElements.whenDefined('sp-overlay').then(() => {
            initOverlay();
        });
    });
</script>

Starting with no DOM in the <sp-overlay> element and returning to that when the Overlay element is no longer showing can support an application in releasing memory back to other activities.