more tweaks

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

@@ -7,9 +7,7 @@ const has_browser_globals = typeof window !== 'undefined';
 // We cache the Node and Element prototype methods, so that subsequent calls-sites are monomorphic rather
 // than megamorphic.
 const node_prototype = /** @type {Node} */ (has_browser_globals ? Node.prototype : {});
-const html_element_prototype = /** @type {Element} */ (
-	has_browser_globals ? HTMLElement.prototype : {}
-);
+const element_prototype = /** @type {Element} */ (has_browser_globals ? Element.prototype : {});
 const text_prototype = /** @type {Text} */ (has_browser_globals ? Text.prototype : {});
 const map_prototype = Map.prototype;
 const append_child_method = node_prototype.appendChild;
@@ -18,11 +16,11 @@ const map_set_method = map_prototype.set;
 const map_get_method = map_prototype.get;
 const map_delete_method = map_prototype.delete;
 // @ts-expect-error improve perf of expando on DOM events
-html_element_prototype.__click = undefined;
+element_prototype.__click = undefined;
 // @ts-expect-error improve perf of expando on DOM text updates
 text_prototype.__nodeValue = ' ';
 // @ts-expect-error improve perf of expando on DOM className updates
-html_element_prototype.__className = '';
+element_prototype.__className = '';
 
 const first_child_get = /** @type {(this: Node) => ChildNode | null} */ (
 	// @ts-ignore
@@ -39,6 +37,11 @@ const text_content_set = /** @type {(this: Node, text: string ) => void} */ (
 	has_browser_globals ? get_descriptor(node_prototype, 'textContent').set : null
 );
 
+const class_name_set = /** @type {(this: Element, class_name: string) => void} */ (
+	// @ts-ignore
+	has_browser_globals ? get_descriptor(element_prototype, 'className').set : null
+);
+
 /**
  * @template {Element} E
  * @template {Node} T
@@ -144,6 +147,16 @@ export function sibling(node) {
 	return next_sibling;
 }
 
+/**
+ * @template {Element} N
+ * @param {N} node
+ * @param {string} class_name
+ * @returns {void}
+ */
+export function set_class_name(node, class_name) {
+	class_name_set.call(node, class_name);
+}
+
 /**
  * @template {Node} N
  * @param {N} node

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

@@ -1,5 +1,13 @@
 import { DEV } from 'esm-env';
-import { append_child, child, clone_node, create_element, map_get, map_set } from './operations.js';
+import {
+	append_child,
+	child,
+	clone_node,
+	create_element,
+	map_get,
+	map_set,
+	set_class_name
+} from './operations.js';
 import {
 	create_root_block,
 	create_each_item_block,
@@ -349,7 +357,7 @@ export function class_name(dom, value) {
 		if (next_class_name === '') {
 			dom.removeAttribute('class');
 		} else {
-			dom.className = next_class_name;
+			set_class_name(dom, next_class_name);
 		}
 		// @ts-expect-error need to add __className to patched prototype
 		dom.__className = next_class_name;