svelte/sites/svelte-5-preview/src/routes/docs/content/01-api/05-functions.md

title
Functions

As well as runes, Svelte 5 will introduce a couple of new functions, in addition to existing functions like getContext, setContext and tick. These are introduced as functions rather than runes because they are used directly and the compiler does not need to touch them to make them function as it does with runes. However, these functions may still use Svelte internals.

untrack

To prevent something from being treated as an $effect/$derived dependency, use untrack:

<script>
	import { untrack } from 'svelte';

	let { a, b } = $props();

	$effect(() => {
		// this will run when `a` changes,
		// but not when `b` changes
		console.log(a);
		console.log(untrack(() => b));
	});
</script>

unstate

To remove reactivity from objects and arrays created with $state, use unstate:

<script>
	import { unstate } from 'svelte';

	let counter = $state({ count: 0 });

	$effect(() => {
		// Will log { count: 0 }
		console.log(unstate(counter));
	});
</script>

This is handy when you want to pass some state to an external library or API that doesn't expect a reactive object – such as structuredClone.