function untrack(fn) {
	var previous_untracking = untracking;
	try {
		untracking = true;
		return fn();
	} finally {
		untracking = previous_untracking;
	}
}
When used inside a [`$derived`](https://svelte.dev/docs/svelte/$derived) or [`$effect`](https://svelte.dev/docs/svelte/$effect),
any state read inside `fn` will not be treated as a dependency.

```ts
$effect(() => {
  // this will run when `data` changes, but not when `time` changes
  save(data, {
    timestamp: untrack(() => time)
  });
});
```
@template T
@param {() => T} fn
@returns {T}