chore: make reactions a Set

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

@@ -219,10 +219,9 @@ function mark_reactions(signal, status) {
 	if (reactions === null) return;
 
 	var runes = is_runes();
-	var length = reactions.length;
+	var length = reactions.size;
 
-	for (var i = 0; i < length; i++) {
-		var reaction = reactions[i];
+	for (var reaction of reactions) {
 		var flags = reaction.f;
 
 		// Skip any effects that are already dirty

packages/svelte/src/internal/client/reactivity/types.d.ts

@@ -9,7 +9,7 @@ export interface Signal {
 
 export interface Value<V = unknown> extends Signal {
 	/** Signals that read from this signal */
-	reactions: null | Reaction[];
+	reactions: null | Set<Reaction>;
 	/** Equality function */
 	equals: Equals;
 	/** The latest value for this signal */

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

@@ -187,7 +187,7 @@ export function check_dirtiness(reaction) {
 
 			if ((flags & DISCONNECTED) !== 0) {
 				for (i = 0; i < dependencies.length; i++) {
-					(dependencies[i].reactions ??= []).push(reaction);
+					(dependencies[i].reactions ??= new Set()).add(reaction);
 				}
 
 				reaction.f ^= DISCONNECTED;
@@ -207,9 +207,9 @@ export function check_dirtiness(reaction) {
 					is_unowned &&
 					active_effect !== null &&
 					!skip_reaction &&
-					!dependency?.reactions?.includes(reaction)
+					!dependency?.reactions?.has(reaction)
 				) {
-					(dependency.reactions ??= []).push(reaction);
+					(dependency.reactions ??= new Set()).add(reaction);
 				}
 
 				if (dependency.version > reaction.version) {
@@ -333,7 +333,7 @@ export function update_reaction(reaction) {
 
 			if (!skip_reaction) {
 				for (i = skipped_deps; i < deps.length; i++) {
-					(deps[i].reactions ??= []).push(reaction);
+					(deps[i].reactions ??= new Set()).add(reaction);
 				}
 			}
 		} else if (deps !== null && skipped_deps < deps.length) {
@@ -362,15 +362,13 @@ export function update_reaction(reaction) {
 function remove_reaction(signal, dependency) {
 	let reactions = dependency.reactions;
 	if (reactions !== null) {
-		var index = reactions.indexOf(signal);
-		if (index !== -1) {
-			var new_length = reactions.length - 1;
+		if (reactions.has(signal)) {
+			var new_length = reactions.size - 1;
 			if (new_length === 0) {
 				reactions = dependency.reactions = null;
 			} else {
 				// Swap with last element and then remove.
-				reactions[index] = reactions[new_length];
-				reactions.pop();
+				reactions.delete(signal);
 			}
 		}
 	}

packages/svelte/src/reactivity/map.js

@@ -105,7 +105,11 @@ export class SvelteMap extends Map {
 			increment(s);
 
 			// if not every reaction of s is a reaction of version we need to also include version
-			const needs_version_increase = !s.reactions?.every((r) => version.reactions?.includes(r));
+			const needs_version_increase =
+				version.reactions !== null &&
+				!(s.reactions === null ? [] : [...s.reactions.values()]).every((reaction) =>
+					version.reactions?.has(reaction)
+				);
 			if (needs_version_increase) {
 				increment(version);
 			}

packages/svelte/tests/signals/test.ts

@@ -238,13 +238,13 @@ describe('signals', () => {
 		return () => {
 			flushSync(() => set(count, 1));
 			// Ensure we're not leaking consumers
-			assert.deepEqual(count.reactions?.length, 1);
+			assert.deepEqual(count.reactions?.size, 1);
 			flushSync(() => set(count, 2));
 			// Ensure we're not leaking consumers
-			assert.deepEqual(count.reactions?.length, 1);
+			assert.deepEqual(count.reactions?.size, 1);
 			flushSync(() => set(count, 3));
 			// Ensure we're not leaking consumers
-			assert.deepEqual(count.reactions?.length, 1);
+			assert.deepEqual(count.reactions?.size, 1);
 			assert.deepEqual(log, [0, 1, 2, 3]);
 		};
 	});
@@ -306,8 +306,8 @@ describe('signals', () => {
 			flushSync(() => set(count, 4));
 			flushSync(() => set(count, 0));
 			// Ensure we're not leaking consumers
-			assert.deepEqual(count.reactions?.length, 2);
-			assert.deepEqual(calc.reactions?.length, 1);
+			assert.deepEqual(count.reactions?.size, 2);
+			assert.deepEqual(calc.reactions?.size, 1);
 			assert.deepEqual(log, [0, 2, 'limit', 0]);
 			destroy();
 			// Ensure we're not leaking consumers
@@ -486,7 +486,7 @@ describe('signals', () => {
 		return () => {
 			flushSync();
 			assert.equal(a?.deps?.length, 1);
-			assert.equal(s?.reactions?.length, 1);
+			assert.equal(s?.reactions?.size, 1);
 			destroy();
 			assert.equal(s?.reactions, null);
 		};
@@ -659,12 +659,12 @@ describe('signals', () => {
 			});
 
 			assert.equal($.get(d), 0);
-			assert.equal(count.reactions?.length, 1);
+			assert.equal(count.reactions?.size, 1);
 			assert.equal(d.deps?.length, 1);
 
 			set(count, 1);
 			assert.equal($.get(d), 2);
-			assert.equal(count.reactions?.length, 1);
+			assert.equal(count.reactions?.size, 1);
 			assert.equal(d.deps?.length, 1);
 
 			destroy();