alternative approach

packages/svelte/src/internal/client/dom/elements/bindings/this.js

@@ -1,12 +1,7 @@
 import { STATE_SYMBOL } from '../../../constants.js';
-import { branch, effect, render_effect } from '../../../reactivity/effects.js';
-import {
-	current_effect,
-	current_reaction,
-	set_current_effect,
-	set_current_reaction,
-	untrack
-} from '../../../runtime.js';
+import { effect, render_effect } from '../../../reactivity/effects.js';
+import { untrack } from '../../../runtime.js';
+import { queue_task } from '../../task.js';
 
 /**
  * @param {any} bound_value
@@ -53,18 +48,12 @@ export function bind_this(element_or_component, update, get_value, get_parts) {
 		});
 
 		return () => {
-			const previous_effect = current_effect;
-			const previous_reaction = current_reaction;
-			// TODO: maybe we should use something other an effect branch here to emulate the microtask behaviour.
-			set_current_effect(null);
-			set_current_reaction(null);
-			branch(() => {
+			// We cannot use effects in the teardown phase, we we use a microtask instead.
+			queue_task(() => {
 				if (parts && is_bound_this(get_value(...parts), element_or_component)) {
 					update(null, ...parts);
 				}
 			});
-			set_current_effect(previous_effect);
-			set_current_reaction(previous_reaction);
 		};
 	});
 }

packages/svelte/src/internal/client/dom/task.js

@@ -1,12 +1,9 @@
 import { run_all } from '../../shared/utils.js';
 
 let is_task_queued = false;
-let is_raf_queued = false;
 
 /** @type {Array<() => void>} */
 let current_queued_tasks = [];
-/** @type {Array<() => void>} */
-let current_raf_tasks = [];
 
 function process_task() {
 	is_task_queued = false;
@@ -15,11 +12,15 @@ function process_task() {
 	run_all(tasks);
 }
 
-function process_raf_task() {
-	is_raf_queued = false;
-	const tasks = current_raf_tasks.slice();
-	current_raf_tasks = [];
-	run_all(tasks);
+/**
+ * @param {() => void} fn
+ */
+export function queue_task(fn) {
+	if (!is_task_queued) {
+		is_task_queued = true;
+		queueMicrotask(process_task);
+	}
+	current_queued_tasks.push(fn);
 }
 
 /**
@@ -29,7 +30,4 @@ export function flush_tasks() {
 	if (is_task_queued) {
 		process_task();
 	}
-	if (is_raf_queued) {
-		process_raf_task();
-	}
 }

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

@@ -669,11 +669,11 @@ export function flush_sync(fn, flush_previous = true) {
 
 		var result = fn?.();
 
+		flush_tasks();
 		if (current_queued_root_effects.length > 0 || root_effects.length > 0) {
 			flush_sync();
 		}
 
-		flush_tasks();
 		flush_count = 0;
 
 		return result;

packages/svelte/tests/runtime-legacy/samples/ondestroy-before-cleanup/_config.js

@@ -8,6 +8,6 @@ export default test({
 		const div = target.querySelector('div');
 
 		component.visible = false;
-		assert.equal(container.div, null);
+		assert.equal(container.div, div);
 	}
 });