From 435a9c1cd033dc4a31af9ba007eb7f5b6e24c488 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Wed, 30 Oct 2024 11:02:18 +0000
Subject: [PATCH] fix: ensure toStore subscription correctly syncs latest value
 (#14015)

* fix: ensure toStore subscription correctly syncs latest value

* Update packages/svelte/src/store/index-client.js

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/shaggy-frogs-fetch.md                   |  5 +++++
 packages/svelte/src/store/index-client.js          |  7 +++++--
 .../samples/toStore-subscribe/_config.js           |  6 ++++++
 .../samples/toStore-subscribe/main.svelte          | 14 ++++++++++++++
 4 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/shaggy-frogs-fetch.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/toStore-subscribe/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/toStore-subscribe/main.svelte

diff --git a/.changeset/shaggy-frogs-fetch.md b/.changeset/shaggy-frogs-fetch.md
new file mode 100644
index 0000000000..7dc7b8b920
--- /dev/null
+++ b/.changeset/shaggy-frogs-fetch.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure toStore subscription correctly syncs latest value
diff --git a/packages/svelte/src/store/index-client.js b/packages/svelte/src/store/index-client.js
index 98f6cf5ac1..f2f1dfc4eb 100644
--- a/packages/svelte/src/store/index-client.js
+++ b/packages/svelte/src/store/index-client.js
@@ -42,8 +42,11 @@ export { derived, get, readable, readonly, writable } from './shared/index.js';
  * @returns {Writable<V> | Readable<V>}
  */
 export function toStore(get, set) {
-	const store = writable(get(), (set) => {
-		let ran = false;
+	let init_value = get();
+	const store = writable(init_value, (set) => {
+		// If the value has changed before we call subscribe, then
+		// we need to treat the value as already having run
+		let ran = init_value !== get();
 
 		// TODO do we need a different implementation on the server?
 		const teardown = effect_root(() => {
diff --git a/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/_config.js b/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/_config.js
new file mode 100644
index 0000000000..471fed7e09
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/_config.js
@@ -0,0 +1,6 @@
+import { test } from '../../test';
+
+export default test({
+	html: `1`,
+	mode: ['client', 'hydrate']
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/main.svelte b/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/main.svelte
new file mode 100644
index 0000000000..61e0cbe5b6
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/toStore-subscribe/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	import { toStore } from 'svelte/store';
+
+	let count = $state(0);
+
+	const store = toStore(
+		() => count,
+		(v) => (count = v)
+	);
+
+	store.set(1);
+</script>
+
+{$store}