Issue with Reactivity in count2 in Asynchronous Code

[origin721]

Describe the bug

Hi Svelte Team,

I hope you're doing well! I’ve encountered an issue with reactivity in Svelte related to asynchronous updates, specifically with count2 not triggering as expected. I’m not sure if this is a known behavior or a bug, so I wanted to share the details.

Here’s the code I’m working with:

<script>
	let count = $state(0);
	let count2 = $state(0);
	
	function increment() {
		count += 1; 
	}

	$effect(async() => {
		await new Promise((res) => setTimeout(res, 1000));
		count2 = count - 1
	});
</script>

<button onclick={increment}>ok</button>
<div>{count}</div>
<div>{count2}</div>

Issue:
When increment is called, count updates correctly after the delay, and the UI reflects the new value.

However, the $effect block, which depends on count, doesn’t seem to trigger reactivity for count2. The value of count2 doesn’t update in the UI, even though count has changed.

Expected Behavior:
The $effect block should re-run whenever count changes, and count2 should update reactively in the UI.

Is this a known limitation, or is there something I’m missing in how Svelte handles asynchronous reactivity in $effect? Any insights or suggestions would be greatly appreciated!

Thank you for your time and for all the incredible work on Svelte!

Reproduction

<script>
	let count = $state(0);
	let count2 = $state(0);
	
	function increment() {
		count += 1; 
	}

	$effect(async() => {
		await new Promise((res) => setTimeout(res, 1000));
		count2 = count - 1
	});
</script>

<button onclick={increment}>ok</button>
<div>{count}</div>
<div>{count2}</div>

Logs

System Info

https://svelte.dev/tutorial/svelte/welcome-to-svelte

Severity

annoyance

[Conduitry]

This is expected: #10498 / #10959

It's also documented: https://svelte.dev/docs/svelte/$effect#Understanding-dependencies