From 3c155e3f3e930408b7c8fdd3d8423b3d6efdb3d6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 2 Apr 2024 05:16:54 -0400
Subject: [PATCH] fix: ensure effect cleanup functions are called with null
 `this` (#11024)

---
 .changeset/fuzzy-donuts-provide.md                           | 5 +++++
 packages/svelte/src/internal/client/reactivity/effects.js    | 2 +-
 packages/svelte/src/internal/client/runtime.js               | 2 +-
 .../tests/runtime-runes/samples/effect-cleanup/_config.js    | 2 +-
 .../tests/runtime-runes/samples/effect-cleanup/main.svelte   | 4 +++-
 5 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/fuzzy-donuts-provide.md

diff --git a/.changeset/fuzzy-donuts-provide.md b/.changeset/fuzzy-donuts-provide.md
new file mode 100644
index 000000000000..ae5333e6ecd9
--- /dev/null
+++ b/.changeset/fuzzy-donuts-provide.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure effect cleanup functions are called with null `this`
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index fd478fc3dce5..5506737e3172 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -244,7 +244,7 @@ export function destroy_effect(effect) {
 		}
 	}
 
-	effect.teardown?.();
+	effect.teardown?.call(null);
 
 	if (effect.dom !== null) {
 		remove(effect.dom);
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 8f4c275810f4..d3d7e88412aa 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -391,7 +391,7 @@ export function execute_effect(effect) {
 			destroy_effect_children(effect);
 		}
 
-		effect.teardown?.();
+		effect.teardown?.call(null);
 		var teardown = execute_reaction_fn(effect);
 		effect.teardown = typeof teardown === 'function' ? teardown : null;
 	} finally {
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
index b745e0de3d2f..e61a6bffdda7 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/_config.js
@@ -15,6 +15,6 @@ export default test({
 		flushSync(() => {
 			b1.click();
 		});
-		assert.deepEqual(log, ['init 0', 'cleanup 2', 'init 2', 'cleanup 4', 'init 4']);
+		assert.deepEqual(log, ['init 0', 'cleanup 2', null, 'init 2', 'cleanup 4', null, 'init 4']);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
index a67624b76015..1a5f7b632ff0 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/effect-cleanup/main.svelte
@@ -8,8 +8,10 @@
 
 		log.push('init ' + double);
 
-		return () => {
+		return function() {
 			log.push('cleanup ' + double);
+			// @ts-expect-error
+			log.push(this);
 		};
 	})
 </script>