feat: add $effect.active rune

[trueadm]

We used to have this rune a while ago, back when it worked like $effect.tracking, this time it's back but operates differently. Now it will let you know if you're inside an active effect context. This is super useful for validation patterns where you want to warn people that some utility or API requires usage in specific parts of the codebase – such as a component or another effect.

function my_util() {
  if (!$effect.active()) {
    throw new Error('more useful error message');
  }

  $effect(() => {
    // do util stuff
  });
}

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Playground

pnpm add https://pkg.pr.new/svelte@14757

[leonidaz]

So, basically active() will always be true if code is running inside a component instance, including inside $effect, $effect.root, or anywhere in external code if called from a component instance or inside external $effect or $effect.root. Calling from the module level code in a component will return false.

tracking() will only be true if it runs inside user or template effects, and in effects inside external root. Inside $effect.root or module will always be false.

Very nice!

Arguably, this seems more useful than effect.tracking but I can see that both may be needed depending on a use case.

bunch of use cases

[trueadm]

So, basically active() will always be true if code is running inside a component instance, including inside $effect, $effect.root, or anywhere in external code if called from a component instance or inside external $effect or $effect.root. Calling from the module level code in a component will return false.

tracking() will only be true if it runs inside user or template effects, and in effects inside external root. Inside $effect.root or module will always be false.

Very nice!

Arguably, this seems more useful than effect.tracking but I can see that both may be needed depending on use case.

bunch of use cases

Essentially, yes. There's also some edge cases it handles. Like used in the teardown of an effect, or inside a derived that is "unowned", i.e. created outside of an effect.

[webJose]

Hello. Will this cover #14329 ?

[leonidaz]

Essentially, yes. There's also some edge cases it handles. Like used in the teardown of an effect, or inside a derived that is "unowned", i.e. created outside of an effect.

cool, in those cases: teardowns and unowned deriveds, both would be false.

updated use cases: bunch of use cases

[leonidaz]

Hello. Will this cover #14329 ?

yeah, it covers anything within a component instance or outside of it if called from the instance. I created a playground with with console.log to compare tracking() vs active() for different use cases: bunch of use cases

[levibassey]

yeah, it covers anything within a component instance or outside of it if called from the instance. I created a playground with with console.log to compare tracking() vs active() for different use cases: bunch of use cases

Shouldn't $effect.active() return false if it's in the module scope?

<script module>
	console.log('active -- module component', $effect.active()) // true (Should be false)
	console.log('tracking -- module component', $effect.tracking()) // false
</script>

since there are no active effects

[leonidaz]

yeah, it covers anything within a component instance or outside of it if called from the instance. I created a playground with with console.log to compare tracking() vs active() for different use cases: bunch of use cases

Shouldn't $effect.active() return false if it's in the module scope?

<script module>
	console.log('active -- module component', $effect.active()) // true (Should be false)
	console.log('tracking -- module component', $effect.tracking()) // false
</script>

since there are no active effects

sorry, this is just a typo in the comment, copy and paste. yes, both are always false in modules. updated