svelte/documentation/examples/17-special-elements/05-svelte-document/App.svelte

<script>
	let selection = '';

	const handleSelectionChange = (e) => (selection = document.getSelection());
</script>

<svelte:document on:selectionchange={handleSelectionChange} />

<p>Select this text to fire events</p>
<p>Selection: {selection}</p>