From d73c5b8434b054022b36d2634b7dfdd161f4f9c2 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Tue, 23 Jul 2024 14:49:26 +0100
Subject: [PATCH] fix: ensure $state.snapshot correctly clones Date objects
 (#12564)

---
 .changeset/dirty-pianos-eat.md                   |  5 +++++
 packages/svelte/src/internal/shared/clone.js     |  4 ++++
 .../samples/state-snapshot-date/_config.js       |  5 +++++
 .../samples/state-snapshot-date/main.svelte      | 16 ++++++++++++++++
 4 files changed, 30 insertions(+)
 create mode 100644 .changeset/dirty-pianos-eat.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-snapshot-date/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/state-snapshot-date/main.svelte

diff --git a/.changeset/dirty-pianos-eat.md b/.changeset/dirty-pianos-eat.md
new file mode 100644
index 0000000000..4bc34bd440
--- /dev/null
+++ b/.changeset/dirty-pianos-eat.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure $state.snapshot correctly clones Date objects
diff --git a/packages/svelte/src/internal/shared/clone.js b/packages/svelte/src/internal/shared/clone.js
index 2d4455714e..9983ef619a 100644
--- a/packages/svelte/src/internal/shared/clone.js
+++ b/packages/svelte/src/internal/shared/clone.js
@@ -79,6 +79,10 @@ function clone(value, cloned, path, paths) {
 			return copy;
 		}
 
+		if (value instanceof Date) {
+			return /** @type {Snapshot<T>} */ (structuredClone(value));
+		}
+
 		if (typeof (/** @type {T & { toJSON?: any } } */ (value).toJSON) === 'function') {
 			return clone(
 				/** @type {T & { toJSON(): any } } */ (value).toJSON(),
diff --git a/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/_config.js b/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/_config.js
new file mode 100644
index 0000000000..c81d77a9e1
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/_config.js
@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: `true\ntrue\ntrue\ntrue`
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/main.svelte b/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/main.svelte
new file mode 100644
index 0000000000..341ec9b110
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/state-snapshot-date/main.svelte
@@ -0,0 +1,16 @@
+<script>
+	let test = $state({
+		a: new Date()
+	});
+	let test2 = $state.snapshot(test);
+
+	let test3 = {
+		a: new Date()
+	}
+	let test4 = structuredClone(test3);
+</script>
+
+{test.a instanceof Date}
+{test2.a instanceof Date}
+{test3.a instanceof Date}
+{test4.a instanceof Date}