during traversal, add effects directly to flush queue rather than scheduling them

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

@@ -69,6 +69,9 @@ let last_scheduled_effect = null;
 let is_flushing = false;
 export let is_flushing_sync = false;
 
+/** @type {Effect[] | null} */
+export let current_effects = null;
+
 export class Batch {
 	/**
 	 * The current values of any sources that are updated in this batch
@@ -185,7 +188,7 @@ export class Batch {
 		this.apply();
 
 		/** @type {Effect[]} */
-		var effects = [];
+		var effects = (current_effects = []);
 
 		/** @type {Effect[]} */
 		var render_effects = [];
@@ -199,6 +202,8 @@ export class Batch {
 			// log_inconsistent_branches(root);
 		}
 
+		current_effects = null;
+
 		if (this.#is_deferred()) {
 			this.#defer_effects(render_effects);
 			this.#defer_effects(effects);

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

@@ -40,7 +40,7 @@ import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { component_context, dev_current_component_function, dev_stack } from '../context.js';
-import { Batch, schedule_effect } from './batch.js';
+import { Batch, current_effects, schedule_effect } from './batch.js';
 import { flatten, increment_pending } from './async.js';
 import { without_reactive_context } from '../dom/elements/bindings/shared.js';
 import { set_signal_status } from './status.js';
@@ -127,8 +127,12 @@ function create_effect(type, fn, sync) {
 			throw e;
 		}
 	} else if (fn !== null) {
-		Batch.ensure();
-		schedule_effect(effect);
+		if (current_effects !== null) {
+			current_effects.push(effect);
+		} else {
+			Batch.ensure();
+			schedule_effect(effect);
+		}
 	}
 
 	/** @type {Effect | null} */