Trap suggestions in use: documentation

[Fd929c2CE5fA]

https://svelte.dev/docs/svelte/use

According to the Svelte 5 documentation's description of use:, it implies that return {update, destroy} is replaced by $effect.

https://svelte.dev/docs/svelte/$effect

But in fact, according to the documentation for $effect, the return in $effect actually runs when it is destroyed and effect re-runs.

It is different from destroy behavior in use: return, cannot be replaced directly, and may cause unexpected behavior.

When the expected destroy is only run when the element is destroyed, using $effect as recommended may lead to unexpected behavior.

Here is an example of the different behaviors of the two: Playground

[brunnerh]

I would recommend directly opening an issue if you think some aspect of the docs is incomplete or can be improved.

Regarding $effects and actions, you can model the destroy behavior via $effect but you probably would want separate effects for update and destroy.

$effect(() => console.log("update-$effect", count1));
$effect(() => {
	return () => {
		console.log("destroy-$effect", count1);
		count1 = 0;
	}
});

Adjusted playground example

[Fd929c2CE5fA]

Thanks, splitting $effect is a good point.

But I think it's still not as intuitive as return {update, destroy} in action.

It can easily become difficult to understand unless I remember:

• The first $effect is used for updates
• The second $effect is used for destruction
• And they rely on the implicit parent $effect of the action

And the return {update, destroy} except for need explicitly passing arguments into the action, all aspects have become much more intuitive.

Unless I'm very familiar with $effect and remember all the logic behind it, and expect other code readers to have the same background knowledge, here I might prefer to use the old return {update, destroy}.

Anyway, thanks again!