From f0576ea01f65c062c3d948475b121620568edd52 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 8 May 2026 10:40:05 -0400
Subject: [PATCH] add test and note-to-self about store behaviour with async

---
 .../src/internal/client/reactivity/batch.js   |  2 +-
 .../_config.js                                | 52 +++++++++++++++++++
 .../main.svelte                               | 29 +++++++++++
 3 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/main.svelte

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 8f14cb4437..f5f16e101d 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -301,7 +301,7 @@ export class Batch {
 
 		/**
 		 * @type {Effect[]}
-		 * @deprecated when we get rid of legacy mode and stores, we can get rid of this
+		 * @deprecated when we get rid of legacy mode and stores, we can get rid of this, and also early-return in the deferred case
 		 */
 		var updates = (legacy_updates = []);
 
diff --git a/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/_config.js b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/_config.js
new file mode 100644
index 0000000000..4a36e05b8c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/_config.js
@@ -0,0 +1,52 @@
+import { tick } from 'svelte';
+import { ok, test } from '../../test';
+
+// Test that the store is unsubscribed from, even if it's not referenced once the store itself is set to null
+export default test({
+	async test({ target, assert }) {
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>0</p> <button>add watcher</button>`
+		);
+
+		target.querySelector('button')?.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>1</p> hello 1 <button>remove watcher</button>`
+		);
+
+		const input = target.querySelector('input');
+		ok(input);
+
+		input.stepUp();
+		input.dispatchEvent(new Event('input', { bubbles: true }));
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>2</p> hello 2 <button>remove watcher</button>`
+		);
+
+		target.querySelector('button')?.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>2</p> <button>add watcher</button>`
+		);
+
+		input.stepUp();
+		input.dispatchEvent(new Event('input', { bubbles: true }));
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>2</p> <button>add watcher</button>`
+		);
+
+		target.querySelector('button')?.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<input type="number"> <p>3</p> hello 3 <button>remove watcher</button>`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/main.svelte
new file mode 100644
index 0000000000..4abfd3c2f9
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after-2/main.svelte
@@ -0,0 +1,29 @@
+<script>
+	import { writable, derived } from "svelte/store";
+
+	const obj = writable({ a: 1 });
+	let count = $state(0);
+	let watcherA = $state();
+
+	function watch (prop) {
+		return derived(obj, (o) => {
+			count++;
+			return o[prop];
+		});
+	}
+</script>
+
+<input type="number" bind:value={$obj.a}>
+<p>{count}</p>
+
+{#if watcherA}
+	<!-- make sure the presence of async work doesn't break the `legacy_updates` mechanism -->
+	{#if true}
+		{await 'hello'}
+	{/if}
+
+	{$watcherA}
+	<button on:click={() => watcherA = null}>remove watcher</button>
+{:else}
+	<button on:click={() => watcherA = watch("a")}>add watcher</button>
+{/if}