Unlike Svelte 4, the current rc version of Svelte 5 executes children actions after parent actions

[divdavem]

Describe the bug

As reported by @quentinderoubaix in the svelte-5-rc discord channel, the current rc version of Svelte 5 (5.0.0-next.258) changes the order of execution of actions compared to Svelte 4.

This breaks one of our actions that depends on the full initialization of its children (including executing their actions) to be able to properly achieve its own work.

Reproduction

<script>
	const action = (element) => {
		console.log(`Action run for element ${element.id}`);
	};
</script>

<div use:action id="0">
	<div use:action id="1">
	</div>
</div>

Check in Svelte 4
Check in Svelte 5

Logs

In Svelte 4:

Action run for element 1
Action run for element 0

In Svelte 5:

Action run for element 0
Action run for element 1

System Info

Tested with Svelte 5.0.0-next.258

Severity

blocking an upgrade

[trueadm]

We can either change the behaviour of actions to match Svelte 4, so child element actions come first – or we can document this change as a breaking change for Svelte 5.

[trueadm]

We've decided to make it work like Svelte 4.