fix: remove memory leak from retaining old DOM elements

.changeset/rich-plums-thank.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: remove memory leak from retaining old DOM elements

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

@@ -1,8 +1,30 @@
 import { derived } from '../../reactivity/deriveds.js';
 import { render_effect } from '../../reactivity/effects.js';
-import { get } from '../../runtime.js';
+import { current_effect, get } from '../../runtime.js';
+import { is_array } from '../../utils.js';
 import { hydrate_nodes, hydrating } from '../hydration.js';
 import { create_fragment_from_html, remove } from '../reconciler.js';
+import { push_template_node } from '../template.js';
+
+/**
+ * @param {import('#client').Effect} effect
+ * @param {(Element | Comment | Text)[]} to_remove
+ * @returns {void}
+ */
+function remove_from_parent_effect(effect, to_remove) {
+	const dom = effect.dom;
+
+	if (is_array(dom)) {
+		for (let i = dom.length - 1; i >= 0; i--) {
+			if (to_remove.includes(dom[i])) {
+				dom.splice(i, 1);
+				break;
+			}
+		}
+	} else if (dom !== null && to_remove.includes(dom)) {
+		effect.dom = null;
+	}
+}
 
 /**
  * @param {Element | Text | Comment} anchor
@@ -11,13 +33,19 @@ import { create_fragment_from_html, remove } from '../reconciler.js';
  * @returns {void}
  */
 export function html(anchor, get_value, svg) {
+	const parent_effect = anchor.parentNode !== current_effect?.dom ? current_effect : null;
 	let value = derived(get_value);
 
 	render_effect(() => {
-		var dom = html_to_dom(anchor, get(value), svg);
+		var dom = html_to_dom(anchor, parent_effect, get(value), svg);
 
 		if (dom) {
-			return () => remove(dom);
+			return () => {
+				if (parent_effect !== null) {
+					remove_from_parent_effect(parent_effect, is_array(dom) ? dom : [dom]);
+				}
+				remove(dom);
+			};
 		}
 	});
 }
@@ -27,11 +55,12 @@ export function html(anchor, get_value, svg) {
  * inserts it before the target anchor and returns the new nodes.
  * @template V
  * @param {Element | Text | Comment} target
+ * @param {import('#client').Effect | null} effect
  * @param {V} value
  * @param {boolean} svg
  * @returns {Element | Comment | (Element | Comment | Text)[]}
  */
-function html_to_dom(target, value, svg) {
+function html_to_dom(target, effect, value, svg) {
 	if (hydrating) return hydrate_nodes;
 
 	var html = value + '';
@@ -49,6 +78,9 @@ function html_to_dom(target, value, svg) {
 	if (node.childNodes.length === 1) {
 		var child = /** @type {Text | Element | Comment} */ (node.firstChild);
 		target.before(child);
+		if (effect !== null) {
+			push_template_node(effect, child);
+		}
 		return child;
 	}
 
@@ -62,5 +94,9 @@ function html_to_dom(target, value, svg) {
 		target.before(node);
 	}
 
+	if (effect !== null) {
+		push_template_node(effect, nodes);
+	}
+
 	return nodes;
 }

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

@@ -13,6 +13,7 @@ import { is_array } from '../../utils.js';
 import { set_should_intro } from '../../render.js';
 import { current_each_item, set_current_each_item } from './each.js';
 import { current_effect } from '../../runtime.js';
+import { push_template_node } from '../template.js';
 
 /**
  * @param {import('#client').Effect} effect
@@ -131,6 +132,8 @@ export function element(anchor, get_tag, is_svg, render_fn) {
 					if (prev_element) {
 						swap_block_dom(parent_effect, prev_element, element);
 						prev_element.remove();
+					} else if (!hydrating) {
+						push_template_node(parent_effect, element);
 					}
 				});
 			}

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

@@ -4,6 +4,36 @@ 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 { effect } from '../reactivity/effects.js';
+import { is_array } from '../utils.js';
+
+/**
+ * @param {import("#client").Effect} effect
+ * @param {import("#client").TemplateNode | import("#client").TemplateNode[]} dom
+ */
+export function push_template_node(effect, dom) {
+	var current_dom = effect.dom;
+	if (current_dom === null) {
+		effect.dom = dom;
+	} else {
+		if (!is_array(current_dom)) {
+			current_dom = effect.dom = [current_dom];
+		}
+		var anchor;
+		// If we're working with an anchor, then remove it and put it at the end.
+		if (current_dom[0].nodeType === 8) {
+			anchor = current_dom.pop();
+		}
+		if (is_array(dom)) {
+			current_dom.push(...dom);
+		} else {
+			current_dom.push(dom);
+		}
+		if (anchor !== undefined) {
+			current_dom.push(anchor);
+		}
+	}
+	return dom;
+}
 
 /**
  * @param {string} content
@@ -19,16 +49,31 @@ export function template(content, flags) {
 	var node;
 
 	return () => {
+		var effect = /** @type {import('#client').Effect} */ (current_effect);
 		if (hydrating) {
-			return is_fragment ? hydrate_nodes : /** @type {Node} */ (hydrate_nodes[0]);
+			var hydration_content = push_template_node(
+				effect,
+				is_fragment ? hydrate_nodes : hydrate_nodes[0]
+			);
+			return /** @type {Node} */ (hydration_content);
 		}
 
 		if (!node) {
 			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);
+
+		if (is_fragment) {
+			push_template_node(
+				effect,
+				/** @type {import('#client').TemplateNode[]} */ ([...clone.childNodes])
+			);
+		} else {
+			push_template_node(effect, /** @type {import('#client').TemplateNode} */ (clone));
+		}
 
-		return use_import_node ? document.importNode(node, true) : clone_node(node, true);
+		return clone;
 	};
 }
 
@@ -70,8 +115,13 @@ export function svg_template(content, flags) {
 	var node;
 
 	return () => {
+		var effect = /** @type {import('#client').Effect} */ (current_effect);
 		if (hydrating) {
-			return is_fragment ? hydrate_nodes : /** @type {Node} */ (hydrate_nodes[0]);
+			var hydration_content = push_template_node(
+				effect,
+				is_fragment ? hydrate_nodes : hydrate_nodes[0]
+			);
+			return /** @type {Node} */ (hydration_content);
 		}
 
 		if (!node) {
@@ -87,7 +137,18 @@ export function svg_template(content, flags) {
 			}
 		}
 
-		return clone_node(node, true);
+		var clone = clone_node(node, true);
+
+		if (is_fragment) {
+			push_template_node(
+				effect,
+				/** @type {import('#client').TemplateNode[]} */ ([...clone.childNodes])
+			);
+		} else {
+			push_template_node(effect, /** @type {import('#client').TemplateNode} */ (clone));
+		}
+
+		return clone;
 	};
 }
 
@@ -152,7 +213,8 @@ function run_scripts(node) {
  */
 /*#__NO_SIDE_EFFECTS__*/
 export function text(anchor) {
-	if (!hydrating) return empty();
+	var effect = /** @type {import('#client').Effect} */ (current_effect);
+	if (!hydrating) return push_template_node(effect, empty());
 
 	var node = hydrate_nodes[0];
 
@@ -162,7 +224,7 @@ export function text(anchor) {
 		anchor.before((node = empty()));
 	}
 
-	return node;
+	return push_template_node(effect, node);
 }
 
 export const comment = template('<!>', TEMPLATE_FRAGMENT);
@@ -174,19 +236,7 @@ export const comment = template('<!>', TEMPLATE_FRAGMENT);
  * @param {import('#client').Dom} dom
  */
 export function append(anchor, dom) {
-	var current = dom;
-
 	if (!hydrating) {
-		var node = /** @type {Node} */ (dom);
-
-		if (node.nodeType === 11) {
-			// if hydrating, `dom` is already an array of nodes, but if not then
-			// we need to create an array to store it on the current effect
-			current = /** @type {import('#client').Dom} */ ([...node.childNodes]);
-		}
-
-		anchor.before(node);
+		anchor.before(/** @type {Node} */ (dom));
 	}
-
-	/** @type {import('#client').Effect} */ (current_effect).dom = current;
 }

packages/svelte/tests/runtime-runes/samples/each-dynamic-html/_config.js

@@ -0,0 +1,39 @@
+import { flushSync } from '../../../../src/index-client';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>add item</button><button>make span</button><button>reverse</button>`,
+
+	async test({ assert, target }) {
+		const [btn1, btn2, btn3] = target.querySelectorAll('button');
+
+		flushSync(() => {
+			btn1?.click();
+			btn1?.click();
+			btn1?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>add item</button><button>make span</button><button>reverse</button><div>Item 1</div><div>Item 2</div><div>Item 3</div>`
+		);
+
+		flushSync(() => {
+			btn2?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>add item</button><button>make span</button><button>reverse</button><span>Item 1</span><span>Item 2</span><span>Item 3</span>`
+		);
+
+		flushSync(() => {
+			btn3?.click();
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>add item</button><button>make span</button><button>reverse</button><span>Item 3</span><span>Item 2</span><span>Item 1</span>`
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/each-dynamic-html/main.svelte

@@ -0,0 +1,30 @@
+<script>
+	let items = $state([]);
+
+	function add_item() {
+		items.push({
+			id: items.length,
+			text: 'Item ' + (items.length + 1),
+			html: '<div>Item ' + (items.length + 1) + '</div>',
+			dom: null,
+		})
+	}
+
+	function make_span() {
+		items.forEach(item => {
+			item.html = item.html.replace(/div/g, 'span')
+		})
+	}
+
+	function reverse() {
+		items.reverse();
+	}
+</script>
+
+<button on:click={add_item}>add item</button>
+<button on:click={make_span}>make span</button>
+<button on:click={reverse}>reverse</button>
+
+{#each items as item (item.id)}
+	{@html item.html}
+{/each}