svelte/documentation/docs/99-legacy/21-legacy-$$slots.md

title
$$slots

In runes mode, we know which snippets were provided to a component, as they're just normal props.

In legacy mode, the way to know if content was provided for a given slot is with the $$slots object, whose keys are the names of the slots passed into the component by the parent.

<!--- file: Card.svelte --->
<div>
	<slot name="title" />
	{#if $$slots.description}
		<!-- This <hr> and slot will render only if `slot="description"` is provided. -->
		<hr />
		<slot name="description" />
	{/if}
</div>

<!--- file: App.svelte --->
<Card>
	<h1 slot="title">Blog Post Title</h1>
	<!-- No slot named "description" was provided so the optional slot will not be rendered. -->
</Card>