From 79a0c0d4d8faf305a1c1c536712139f569c9e431 Mon Sep 17 00:00:00 2001
From: jarrednorris <58517737+jarrednorrisdev@users.noreply.github.com>
Date: Tue, 6 Oct 2026 10:30:52 +0100
Subject: [PATCH] fix: attach event handlers that are assigned after a
 top-level `await` in production (#18933)

Fixes #18932
---
 .changeset/late-handlers-wait.md              |  5 +++++
 .../client/visitors/shared/events.js          |  5 +++--
 .../async-event-handler-blockers/_config.js   | 19 +++++++++++++++++++
 .../async-event-handler-blockers/main.svelte  | 19 +++++++++++++++++++
 4 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/late-handlers-wait.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/main.svelte

diff --git a/.changeset/late-handlers-wait.md b/.changeset/late-handlers-wait.md
new file mode 100644
index 0000000000..306a950c43
--- /dev/null
+++ b/.changeset/late-handlers-wait.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: attach event handlers that are assigned after a top-level `await` in production
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/events.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/events.js
index f01bf08694..83c73a0279 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/events.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/events.js
@@ -119,8 +119,9 @@ export function build_event_handler(node, metadata, context) {
 
 		// local variable can be assigned directly
 		// except in dev mode where when need $.apply()
-		// in order to handle warnings.
-		if (!dev && binding?.declaration_kind !== 'import') {
+		// in order to handle warnings, or when it is
+		// assigned after a top-level `await`
+		if (!dev && binding?.declaration_kind !== 'import' && !binding?.blocker) {
 			return handler;
 		}
 	}
diff --git a/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/_config.js b/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/_config.js
new file mode 100644
index 0000000000..f4dcbef823
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/_config.js
@@ -0,0 +1,19 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+	async test({ assert, target, window, logs }) {
+		await new Promise((r) => setTimeout(r));
+		await tick();
+
+		const button = target.querySelector('button');
+		const div = target.querySelector('div');
+
+		button?.click();
+		div?.dispatchEvent(new window.MouseEvent('mouseenter'));
+		window.dispatchEvent(new window.Event('resize'));
+
+		assert.deepEqual(logs, ['click', 'mouseenter', 'resize']);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/main.svelte
new file mode 100644
index 0000000000..16bbac14a8
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-event-handler-blockers/main.svelte
@@ -0,0 +1,19 @@
+<script>
+	// Wait a macrotask to make sure the handlers aren't read before the microtask-Promise.resolve() resolves, masking a bug
+	await new Promise((r) => setTimeout(r));
+
+	function create_handler(name) {
+		return () => {
+			console.log(name);
+		};
+	}
+
+	const onclick = create_handler('click');
+	const onmouseenter = create_handler('mouseenter');
+	const onresize = create_handler('resize');
+</script>
+
+<svelte:window {onresize} />
+
+<button {onclick}>click</button>
+<div {onmouseenter}>hover</div>