From 3dcd3a96be2849e5d341f1e405251e24827d37e4 Mon Sep 17 00:00:00 2001
From: mustafa0x <mustafa.0x@gmail.com>
Date: Sat, 5 Jul 2025 08:43:13 +0300
Subject: [PATCH] fix(client): protect against window being defined but addEv
 undefined (fixes #19307)

---
 packages/vite/src/client/client.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/vite/src/client/client.ts b/packages/vite/src/client/client.ts
index 1db4a49aa2556a..f17c43592c4d5d 100644
--- a/packages/vite/src/client/client.ts
+++ b/packages/vite/src/client/client.ts
@@ -105,7 +105,8 @@ const transport = normalizeModuleRunnerTransport(
 
 let willUnload = false
 if (typeof window !== 'undefined') {
-  window.addEventListener('beforeunload', () => {
+  // window can be misleadingly defined in a worker if using define (see #19307)
+  window.addEventListener?.('beforeunload', () => {
     willUnload = true
   })
 }