fix: always use document.importNode for template cloning

.changeset/shaggy-feet-kick.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: always use document.importNode for template cloning

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

@@ -28,7 +28,6 @@ import {
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED,
 	TEMPLATE_FRAGMENT,
-	TEMPLATE_USE_IMPORT_NODE,
 	TRANSITION_GLOBAL,
 	TRANSITION_IN,
 	TRANSITION_OUT
@@ -1077,10 +1076,6 @@ function create_block(parent, name, nodes, context) {
 		/** @type {import('estree').Expression[]} */
 		const args = [b.template([b.quasi(state.template.join(''), true)], [])];
 
-		if (state.metadata.context.template_needs_import_node) {
-			args.push(b.literal(TEMPLATE_USE_IMPORT_NODE));
-		}
-
 		add_template(template_name, args);
 
 		body.push(b.var(id, b.call(template_name)), ...state.before_init, ...state.init);
@@ -1121,10 +1116,6 @@ function create_block(parent, name, nodes, context) {
 			} else {
 				let flags = TEMPLATE_FRAGMENT;
 
-				if (state.metadata.context.template_needs_import_node) {
-					flags |= TEMPLATE_USE_IMPORT_NODE;
-				}
-
 				add_template(template_name, [
 					b.template([b.quasi(state.template.join(''), true)], []),
 					b.literal(flags)

packages/svelte/src/constants.js

@@ -17,7 +17,6 @@ export const TRANSITION_OUT = 1 << 1;
 export const TRANSITION_GLOBAL = 1 << 2;
 
 export const TEMPLATE_FRAGMENT = 1;
-export const TEMPLATE_USE_IMPORT_NODE = 1 << 1;
 
 export const HYDRATION_START = '[';
 export const HYDRATION_END = ']';

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

@@ -17,8 +17,8 @@ var text_prototype;
 /** @type {typeof Node.prototype.appendChild} */
 var append_child_method;
 
-/** @type {typeof Node.prototype.cloneNode} */
-var clone_node_method;
+/** @type {typeof document.importNode} */
+export var import_node;
 
 /** @type {(this: Node) => ChildNode | null} */
 var first_child_get;
@@ -56,7 +56,7 @@ export function init_operations() {
 	text_prototype = Text.prototype;
 
 	append_child_method = node_prototype.appendChild;
-	clone_node_method = node_prototype.cloneNode;
+	import_node = document.importNode;
 
 	$window = window;
 	$document = document;
@@ -106,18 +106,6 @@ export function init_operations() {
 export function append_child(element, child) {
 	append_child_method.call(element, child);
 }
-
-/**
- * @template {Node} N
- * @param {N} node
- * @param {boolean} deep
- * @returns {N}
- */
-/*#__NO_SIDE_EFFECTS__*/
-export function clone_node(node, deep) {
-	return /** @type {N} */ (clone_node_method.call(node, deep));
-}
-
 /** @returns {Text} */
 export function empty() {
 	return document.createTextNode('');

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

@@ -1,8 +1,8 @@
 import { hydrate_nodes, hydrating } from './hydration.js';
-import { clone_node, empty } from './operations.js';
+import { import_node, empty } from './operations.js';
 import { create_fragment_from_html } from './reconciler.js';
 import { current_effect } from '../runtime.js';
-import { TEMPLATE_FRAGMENT, TEMPLATE_USE_IMPORT_NODE } from '../../../constants.js';
+import { TEMPLATE_FRAGMENT } from '../../../constants.js';
 import { effect } from '../reactivity/effects.js';
 import { is_array } from '../utils.js';
 
@@ -41,7 +41,6 @@ export function push_template_node(
 /*#__NO_SIDE_EFFECTS__*/
 export function template(content, flags) {
 	var is_fragment = (flags & TEMPLATE_FRAGMENT) !== 0;
-	var use_import_node = (flags & TEMPLATE_USE_IMPORT_NODE) !== 0;
 
 	/** @type {Node} */
 	var node;
@@ -55,7 +54,7 @@ export function template(content, flags) {
 			node = create_fragment_from_html(content);
 			if (!is_fragment) node = /** @type {Node} */ (node.firstChild);
 		}
-		var clone = use_import_node ? document.importNode(node, true) : clone_node(node, true);
+		var clone = import_node(node, true);
 
 		push_template_node(
 			is_fragment
@@ -122,7 +121,7 @@ export function svg_template(content, flags) {
 			}
 		}
 
-		var clone = clone_node(node, true);
+		var clone = import_node(node, true);
 
 		push_template_node(
 			is_fragment
@@ -189,7 +188,7 @@ export function mathml_template(content, flags) {
 			}
 		}
 
-		var clone = clone_node(node, true);
+		var clone = import_node(node, true);
 
 		push_template_node(
 			is_fragment