From e3072c9906ecd8f5e8280ed32a193fdb2f0240d4 Mon Sep 17 00:00:00 2001
From: paoloricciuti <ricciutipaolo@gmail.com>
Date: Mon, 7 Jul 2025 22:35:08 +0200
Subject: [PATCH] chore: use WeakRef

---
 packages/svelte/src/reactivity/map.js | 14 ++++++--------
 packages/svelte/src/reactivity/set.js | 14 ++++++--------
 2 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index 64eb2a6276..35946c5b08 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -57,7 +57,7 @@ export class SvelteMap extends Map {
 	#sources = new Map();
 	#version = state(0);
 	#size = state(0);
-	/**@type {Reaction | null} */
+	/**@type {WeakRef<Reaction> | null} */
 	#initial_reaction = null;
 
 	/**
@@ -67,12 +67,10 @@ export class SvelteMap extends Map {
 		super();
 
 		if (active_reaction !== null) {
-			this.#initial_reaction = active_reaction;
-			// since we only need `initial_reaction` as long as we are in a derived/effect we can
-			// safely create a teardown function that will reset it to null and allow for GC
-			teardown(() => {
-				this.#initial_reaction = null;
-			});
+			// we use a WeakRef (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef)
+			// so that if this Map is somehow stored outside of the active reaction,
+			// it will not prevent the reaction from being garbage collected.
+			this.#initial_reaction = new WeakRef(active_reaction);
 		}
 
 		if (DEV) {
@@ -101,7 +99,7 @@ export class SvelteMap extends Map {
 	 * @returns {Source<T>}
 	 */
 	#source(value) {
-		if (this.#initial_reaction === active_reaction) {
+		if (this.#initial_reaction !== null && this.#initial_reaction.deref() === active_reaction) {
 			return state(value);
 		}
 		return source(value);
diff --git a/packages/svelte/src/reactivity/set.js b/packages/svelte/src/reactivity/set.js
index e7c429c22f..66c0151142 100644
--- a/packages/svelte/src/reactivity/set.js
+++ b/packages/svelte/src/reactivity/set.js
@@ -52,7 +52,7 @@ export class SvelteSet extends Set {
 	#version = state(0);
 	#size = state(0);
 
-	/**@type {Reaction | null}*/
+	/**@type {WeakRef<Reaction> | null}*/
 	#initial_reaction = null;
 
 	/**
@@ -62,12 +62,10 @@ export class SvelteSet extends Set {
 		super();
 
 		if (active_reaction !== null) {
-			this.#initial_reaction = active_reaction;
-			// since we only need `initial_reaction` as long as we are in a derived/effect we can
-			// safely create a teardown function that will reset it to null and allow for GC
-			teardown(() => {
-				this.#initial_reaction = null;
-			});
+			// we use a WeakRef (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef)
+			// so that if this Map is somehow stored outside of the active reaction,
+			// it will not prevent the reaction from being garbage collected.
+			this.#initial_reaction = new WeakRef(active_reaction);
 		}
 
 		if (DEV) {
@@ -98,7 +96,7 @@ export class SvelteSet extends Set {
 	 * @returns {Source<T>}
 	 */
 	#source(value) {
-		if (this.#initial_reaction === active_reaction) {
+		if (this.#initial_reaction !== null && this.#initial_reaction.deref() === active_reaction) {
 			return state(value);
 		}
 		return source(value);