chore: improve performance of DOM traversal operations (#12863)

* chore: improve performance of DOM traversal operations

* feedback

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/odd-toys-glow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: improve performance of DOM traversal operations

packages/svelte/src/internal/client/dom/blocks/css-props.js

@@ -1,6 +1,7 @@
 /** @import { TemplateNode } from '#client' */
 import { render_effect, teardown } from '../../reactivity/effects.js';
 import { hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
+import { get_first_child } from '../operations.js';
 
 /**
  * @param {HTMLDivElement | SVGGElement} element
@@ -9,7 +10,7 @@ import { hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
  */
 export function css_props(element, get_styles) {
 	if (hydrating) {
-		set_hydrate_node(/** @type {TemplateNode} */ (element.firstChild));
+		set_hydrate_node(/** @type {TemplateNode} */ (get_first_child(element)));
 	}
 
 	render_effect(() => {

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

@@ -16,7 +16,12 @@ import {
 	set_hydrate_node,
 	set_hydrating
 } from '../hydration.js';
-import { clear_text_content, create_text } from '../operations.js';
+import {
+	clear_text_content,
+	create_text,
+	get_first_child,
+	get_next_sibling
+} from '../operations.js';
 import {
 	block,
 	branch,
@@ -116,7 +121,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 		var parent_node = /** @type {Element} */ (node);
 
 		anchor = hydrating
-			? set_hydrate_node(/** @type {Comment | Text} */ (parent_node.firstChild))
+			? set_hydrate_node(/** @type {Comment | Text} */ (get_first_child(parent_node)))
 			: parent_node.appendChild(create_text());
 	}
 
@@ -510,7 +515,7 @@ function move(item, next, anchor) {
 	var node = /** @type {EffectNodes} */ (item.e.nodes).start;
 
 	while (node !== end) {
-		var next_node = /** @type {TemplateNode} */ (node.nextSibling);
+		var next_node = /** @type {TemplateNode} */ (get_next_sibling(node));
 		dest.before(node);
 		node = next_node;
 	}

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

@@ -8,6 +8,7 @@ import * as w from '../../warnings.js';
 import { hash } from '../../../../utils.js';
 import { DEV } from 'esm-env';
 import { dev_current_component_function } from '../../runtime.js';
+import { get_first_child, get_next_sibling } from '../operations.js';
 
 /**
  * @param {Element} element
@@ -71,7 +72,7 @@ export function html(node, get_value, svg, mathml, skip_warning) {
 					(next.nodeType !== 8 || /** @type {Comment} */ (next).data !== '')
 				) {
 					last = next;
-					next = /** @type {TemplateNode} */ (next.nextSibling);
+					next = /** @type {TemplateNode} */ (get_next_sibling(next));
 				}
 
 				if (next === null) {
@@ -98,17 +99,17 @@ export function html(node, get_value, svg, mathml, skip_warning) {
 			var node = create_fragment_from_html(html);
 
 			if (svg || mathml) {
-				node = /** @type {Element} */ (node.firstChild);
+				node = /** @type {Element} */ (get_first_child(node));
 			}
 
 			assign_nodes(
-				/** @type {TemplateNode} */ (node.firstChild),
+				/** @type {TemplateNode} */ (get_first_child(node)),
 				/** @type {TemplateNode} */ (node.lastChild)
 			);
 
 			if (svg || mathml) {
-				while (node.firstChild) {
-					anchor.before(node.firstChild);
+				while (get_first_child(node)) {
+					anchor.before(/** @type {Node} */ (get_first_child(node)));
 				}
 			} else {
 				anchor.before(node);

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

@@ -12,6 +12,7 @@ import { create_fragment_from_html } from '../reconciler.js';
 import { assign_nodes } from '../template.js';
 import * as w from '../../warnings.js';
 import { DEV } from 'esm-env';
+import { get_first_child, get_next_sibling } from '../operations.js';
 
 /**
  * @template {(node: TemplateNode, ...args: any[]) => void} SnippetFn
@@ -89,9 +90,9 @@ export function createRawSnippet(fn) {
 		} else {
 			var html = snippet.render().trim();
 			var fragment = create_fragment_from_html(html);
-			element = /** @type {Element} */ (fragment.firstChild);
+			element = /** @type {Element} */ (get_first_child(fragment));
 
-			if (DEV && (element.nextSibling !== null || element.nodeType !== 3)) {
+			if (DEV && (get_next_sibling(element) !== null || element.nodeType !== 3)) {
 				w.invalid_raw_snippet_render();
 			}
 

packages/svelte/src/internal/client/dom/blocks/svelte-element.js

@@ -7,7 +7,7 @@ import {
 	set_hydrate_node,
 	set_hydrating
 } from '../hydration.js';
-import { create_text } from '../operations.js';
+import { create_text, get_first_child } from '../operations.js';
 import {
 	block,
 	branch,
@@ -119,7 +119,7 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 					// If hydrating, use the existing ssr comment as the anchor so that the
 					// inner open and close methods can pick up the existing nodes correctly
 					var child_anchor = /** @type {TemplateNode} */ (
-						hydrating ? element.firstChild : element.appendChild(create_text())
+						hydrating ? get_first_child(element) : element.appendChild(create_text())
 					);
 
 					if (hydrating) {

packages/svelte/src/internal/client/dom/blocks/svelte-head.js

@@ -1,6 +1,6 @@
 /** @import { TemplateNode } from '#client' */
 import { hydrate_node, hydrating, set_hydrate_node, set_hydrating } from '../hydration.js';
-import { create_text } from '../operations.js';
+import { create_text, get_first_child, get_next_sibling } from '../operations.js';
 import { block } from '../../reactivity/effects.js';
 import { HEAD_EFFECT } from '../../constants.js';
 import { HYDRATION_START } from '../../../../constants.js';
@@ -32,14 +32,14 @@ export function head(render_fn) {
 
 		// There might be multiple head blocks in our app, so we need to account for each one needing independent hydration.
 		if (head_anchor === undefined) {
-			head_anchor = /** @type {TemplateNode} */ (document.head.firstChild);
+			head_anchor = /** @type {TemplateNode} */ (get_first_child(document.head));
 		}
 
 		while (
 			head_anchor !== null &&
 			(head_anchor.nodeType !== 8 || /** @type {Comment} */ (head_anchor).data !== HYDRATION_START)
 		) {
-			head_anchor = /** @type {TemplateNode} */ (head_anchor.nextSibling);
+			head_anchor = /** @type {TemplateNode} */ (get_next_sibling(head_anchor));
 		}
 
 		// If we can't find an opening hydration marker, skip hydration (this can happen
@@ -47,7 +47,7 @@ export function head(render_fn) {
 		if (head_anchor === null) {
 			set_hydrating(false);
 		} else {
-			head_anchor = set_hydrate_node(/** @type {TemplateNode} */ (head_anchor.nextSibling));
+			head_anchor = set_hydrate_node(/** @type {TemplateNode} */ (get_next_sibling(head_anchor)));
 		}
 	}
 

packages/svelte/src/internal/client/dom/elements/misc.js

@@ -1,5 +1,5 @@
 import { hydrating } from '../hydration.js';
-import { clear_text_content } from '../operations.js';
+import { clear_text_content, get_first_child } from '../operations.js';
 import { queue_micro_task } from '../task.js';
 
 /**
@@ -27,7 +27,7 @@ export function autofocus(dom, value) {
  * @returns {void}
  */
 export function remove_textarea_child(dom) {
-	if (hydrating && dom.firstChild !== null) {
+	if (hydrating && get_first_child(dom) !== null) {
 		clear_text_content(dom);
 	}
 }

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

@@ -7,6 +7,7 @@ import {
 	HYDRATION_START_ELSE
 } from '../../../constants.js';
 import * as w from '../warnings.js';
+import { get_next_sibling } from './operations.js';
 
 /**
  * Use this variable to guard everything related to hydration code so it can be treeshaken out
@@ -39,7 +40,7 @@ export function set_hydrate_node(node) {
 }
 
 export function hydrate_next() {
-	return set_hydrate_node(/** @type {TemplateNode} */ (hydrate_node.nextSibling));
+	return set_hydrate_node(/** @type {TemplateNode} */ (get_next_sibling(hydrate_node)));
 }
 
 /** @param {TemplateNode} node */
@@ -47,7 +48,7 @@ export function reset(node) {
 	if (!hydrating) return;
 
 	// If the node has remaining siblings, something has gone wrong
-	if (hydrate_node.nextSibling !== null) {
+	if (get_next_sibling(hydrate_node) !== null) {
 		w.hydration_mismatch();
 		throw HYDRATION_ERROR;
 	}
@@ -90,7 +91,7 @@ export function remove_nodes() {
 			}
 		}
 
-		var next = /** @type {TemplateNode} */ (node.nextSibling);
+		var next = /** @type {TemplateNode} */ (get_next_sibling(node));
 		node.remove();
 		node = next;
 	}

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

@@ -2,6 +2,7 @@
 import { hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
 import { DEV } from 'esm-env';
 import { init_array_prototype_warnings } from '../dev/equality.js';
+import { get_descriptor } from '../../shared/utils.js';
 
 // export these for reference in the compiled code, making global name deduplication unnecessary
 /** @type {Window} */
@@ -10,6 +11,11 @@ export var $window;
 /** @type {Document} */
 export var $document;
 
+/** @type {() => Node | null} */
+var first_child_getter;
+/** @type {() => Node | null} */
+var next_sibling_getter;
+
 /**
  * Initialize these lazily to avoid issues when using the runtime in a server context
  * where these globals are not available while avoiding a separate server entry point
@@ -23,6 +29,12 @@ export function init_operations() {
 	$document = document;
 
 	var element_prototype = Element.prototype;
+	var node_prototype = Node.prototype;
+
+	// @ts-ignore
+	first_child_getter = get_descriptor(node_prototype, 'firstChild').get;
+	// @ts-ignore
+	next_sibling_getter = get_descriptor(node_prototype, 'nextSibling').get;
 
 	// the following assignments improve perf of lookups on DOM nodes
 	// @ts-expect-error
@@ -53,6 +65,24 @@ export function create_text(value = '') {
 	return document.createTextNode(value);
 }
 
+/**
+ * @template {Node} N
+ * @param {N} node
+ * @returns {Node | null}
+ */
+export function get_first_child(node) {
+	return first_child_getter.call(node);
+}
+
+/**
+ * @template {Node} N
+ * @param {N} node
+ * @returns {Node | null}
+ */
+export function get_next_sibling(node) {
+	return next_sibling_getter.call(node);
+}
+
 /**
  * Don't mark this as side-effect-free, hydration needs to walk all nodes
  * @template {Node} N
@@ -61,10 +91,10 @@ export function create_text(value = '') {
  */
 export function child(node) {
 	if (!hydrating) {
-		return node.firstChild;
+		return get_first_child(node);
 	}
 
-	var child = /** @type {TemplateNode} */ (hydrate_node.firstChild);
+	var child = /** @type {TemplateNode} */ (get_first_child(hydrate_node));
 
 	// Child can be null if we have an element with a single child, like `<p>{text}</p>`, where `text` is empty
 	if (child === null) {
@@ -84,10 +114,10 @@ export function child(node) {
 export function first_child(fragment, is_text) {
 	if (!hydrating) {
 		// when not hydrating, `fragment` is a `DocumentFragment` (the result of calling `open_frag`)
-		var first = /** @type {DocumentFragment} */ (fragment).firstChild;
+		var first = /** @type {DocumentFragment} */ (get_first_child(/** @type {Node} */ (fragment)));
 
 		// TODO prevent user comments with the empty string when preserveComments is true
-		if (first instanceof Comment && first.data === '') return first.nextSibling;
+		if (first instanceof Comment && first.data === '') return get_next_sibling(first);
 
 		return first;
 	}
@@ -114,10 +144,10 @@ export function first_child(fragment, is_text) {
  */
 export function sibling(node, is_text = false) {
 	if (!hydrating) {
-		return /** @type {TemplateNode} */ (node.nextSibling);
+		return /** @type {TemplateNode} */ (get_next_sibling(node));
 	}
 
-	var next_sibling = /** @type {TemplateNode} */ (hydrate_node.nextSibling);
+	var next_sibling = /** @type {TemplateNode} */ (get_next_sibling(hydrate_node));
 
 	var type = next_sibling.nodeType;
 

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

@@ -1,6 +1,6 @@
 /** @import { Effect, EffectNodes, TemplateNode } from '#client' */
 import { hydrate_next, hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
-import { create_text } from './operations.js';
+import { create_text, get_first_child } 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';
@@ -41,7 +41,7 @@ export function template(content, flags) {
 
 		if (!node) {
 			node = create_fragment_from_html(has_start ? content : '<!>' + content);
-			if (!is_fragment) node = /** @type {Node} */ (node.firstChild);
+			if (!is_fragment) node = /** @type {Node} */ (get_first_child(node));
 		}
 
 		var clone = /** @type {TemplateNode} */ (
@@ -49,7 +49,7 @@ export function template(content, flags) {
 		);
 
 		if (is_fragment) {
-			var start = /** @type {TemplateNode} */ (clone.firstChild);
+			var start = /** @type {TemplateNode} */ (get_first_child(clone));
 			var end = /** @type {TemplateNode} */ (clone.lastChild);
 
 			assign_nodes(start, end);
@@ -113,22 +113,22 @@ export function ns_template(content, flags, ns = 'svg') {
 
 		if (!node) {
 			var fragment = /** @type {DocumentFragment} */ (create_fragment_from_html(wrapped));
-			var root = /** @type {Element} */ (fragment.firstChild);
+			var root = /** @type {Element} */ (get_first_child(fragment));
 
 			if (is_fragment) {
 				node = document.createDocumentFragment();
-				while (root.firstChild) {
-					node.appendChild(root.firstChild);
+				while (get_first_child(root)) {
+					node.appendChild(/** @type {Node} */ (get_first_child(root)));
 				}
 			} else {
-				node = /** @type {Element} */ (root.firstChild);
+				node = /** @type {Element} */ (get_first_child(root));
 			}
 		}
 
 		var clone = /** @type {TemplateNode} */ (node.cloneNode(true));
 
 		if (is_fragment) {
-			var start = /** @type {TemplateNode} */ (clone.firstChild);
+			var start = /** @type {TemplateNode} */ (get_first_child(clone));
 			var end = /** @type {TemplateNode} */ (clone.lastChild);
 
 			assign_nodes(start, end);

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

@@ -39,6 +39,7 @@ import { set } from './sources.js';
 import * as e from '../errors.js';
 import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
+import { get_next_sibling } from '../dom/operations.js';
 
 /**
  * @param {'$effect' | '$effect.pre' | '$inspect'} rune
@@ -361,7 +362,7 @@ export function destroy_effect(effect, remove_dom = true) {
 
 		while (node !== null) {
 			/** @type {TemplateNode | null} */
-			var next = node === end ? null : /** @type {TemplateNode} */ (node.nextSibling);
+			var next = node === end ? null : /** @type {TemplateNode} */ (get_next_sibling(node));
 
 			node.remove();
 			node = next;

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

@@ -1,7 +1,13 @@
 /** @import { ComponentContext, Effect, EffectNodes, TemplateNode } from '#client' */
 /** @import { Component, ComponentType, SvelteComponent } from '../../index.js' */
 import { DEV } from 'esm-env';
-import { clear_text_content, create_text, init_operations } from './dom/operations.js';
+import {
+	clear_text_content,
+	create_text,
+	get_first_child,
+	get_next_sibling,
+	init_operations
+} from './dom/operations.js';
 import { HYDRATION_END, HYDRATION_ERROR, HYDRATION_START } from '../../constants.js';
 import { push, pop, current_component_context, current_effect } from './runtime.js';
 import { effect_root, branch } from './reactivity/effects.js';
@@ -102,18 +108,19 @@ export function mount(component, options) {
  * @returns {Exports}
  */
 export function hydrate(component, options) {
+	init_operations();
 	options.intro = options.intro ?? false;
 	const target = options.target;
 	const was_hydrating = hydrating;
 	const previous_hydrate_node = hydrate_node;
 
 	try {
-		var anchor = /** @type {TemplateNode} */ (target.firstChild);
+		var anchor = /** @type {TemplateNode} */ (get_first_child(target));
 		while (
 			anchor &&
 			(anchor.nodeType !== 8 || /** @type {Comment} */ (anchor).data !== HYDRATION_START)
 		) {
-			anchor = /** @type {TemplateNode} */ (anchor.nextSibling);
+			anchor = /** @type {TemplateNode} */ (get_next_sibling(anchor));
 		}
 
 		if (!anchor) {