init

packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js

@@ -150,6 +150,7 @@ export function CallExpression(node, context) {
 
 			break;
 
+		case '$effect.active':
 		case '$effect.tracking':
 			if (node.arguments.length !== 0) {
 				e.rune_invalid_arguments(node, rune);

packages/svelte/src/compiler/phases/3-transform/client/visitors/CallExpression.js

@@ -17,6 +17,9 @@ export function CallExpression(node, context) {
 		case '$host':
 			return b.id('$$props.$$host');
 
+		case '$effect.active':
+			return b.call('$.effect_active');
+
 		case '$effect.tracking':
 			return b.call('$.effect_tracking');
 

packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js

@@ -16,7 +16,7 @@ export function CallExpression(node, context) {
 		return b.void0;
 	}
 
-	if (rune === '$effect.tracking') {
+	if (rune === '$effect.tracking' || rune === '$effect.active') {
 		return b.false;
 	}
 

packages/svelte/src/internal/client/index.js

@@ -107,6 +107,7 @@ export {
 } from './reactivity/deriveds.js';
 export {
 	aborted,
+	effect_active,
 	effect_tracking,
 	effect_root,
 	legacy_pre_effect,

packages/svelte/src/internal/client/reactivity/effects.js

@@ -165,6 +165,20 @@ export function effect_tracking() {
 	return active_reaction !== null && !untracking;
 }
 
+/**
+ * Internal representation of `$effect.active()`
+ * @returns {boolean}
+ */
+export function effect_active() {
+	if (active_reaction === null && active_effect === null) {
+		return false;
+	}
+	if (is_destroying_effect) {
+		return false;
+	}
+	return true;
+}
+
 /**
  * @param {() => void} fn
  */

packages/svelte/src/utils.js

@@ -442,6 +442,7 @@ const RUNES = /** @type {const} */ ([
 	'$props.id',
 	'$bindable',
 	'$effect',
+	'$effect.active',
 	'$effect.pre',
 	'$effect.tracking',
 	'$effect.root',