fix: improve controlled each block cleanup performance (#11839)

.changeset/gentle-ties-fetch.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve controlled each block cleanup performance

packages/svelte/src/internal/client/dom/blocks/each.js

@@ -68,17 +68,20 @@ function pause_effects(items, controlled_anchor, callback) {
 		pause_children(items[i].e, transitions, true);
 	}
 
+	var is_controlled = length > 0 && transitions.length === 0 && controlled_anchor !== null;
 	// If we have a controlled anchor, it means that the each block is inside a single
 	// DOM element, so we can apply a fast-path for clearing the contents of the element.
-	if (length > 0 && transitions.length === 0 && controlled_anchor !== null) {
+	if (is_controlled) {
-		var parent_node = /** @type {Element} */ (controlled_anchor.parentNode);
+		var parent_node = /** @type {Element} */ (
+			/** @type {Element} */ (controlled_anchor).parentNode
+		);
 		clear_text_content(parent_node);
-		parent_node.append(controlled_anchor);
+		parent_node.append(/** @type {Element} */ (controlled_anchor));
 	}
 
 	run_out_transitions(transitions, () => {
 		for (var i = 0; i < length; i++) {
-			destroy_effect(items[i].e);
+			destroy_effect(items[i].e, !is_controlled);
 		}
 
 		if (callback !== undefined) callback();

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

@@ -311,16 +311,17 @@ export function execute_effect_teardown(effect) {
 
 /**
  * @param {import('#client').Effect} effect
+ * @param {boolean} [remove_dom]
  * @returns {void}
  */
-export function destroy_effect(effect) {
+export function destroy_effect(effect, remove_dom = true) {
 	var dom = effect.dom;
 
-	if (dom !== null) {
+	if (dom !== null && remove_dom) {
 		remove(dom);
 	}
 
-	destroy_effect_children(effect);
+	destroy_effect_children(effect, remove_dom);
 	remove_reactions(effect, 0);
 	set_signal_status(effect, DESTROYED);
 

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

@@ -478,16 +478,17 @@ export function remove_reactions(signal, start_index) {
 
 /**
  * @param {import('#client').Reaction} signal
+ * @param {boolean} [remove_dom]
  * @returns {void}
  */
-export function destroy_effect_children(signal) {
+export function destroy_effect_children(signal, remove_dom = true) {
 	let effect = signal.first;
 	signal.first = null;
 	signal.last = null;
 	var sibling;
 	while (effect !== null) {
 		sibling = effect.next;
-		destroy_effect(effect);
+		destroy_effect(effect, remove_dom);
 		effect = sibling;
 	}
 }