From 347eaffd4a9eec87ff1a46caa1ee13290ff1c997 Mon Sep 17 00:00:00 2001
From: Pat Cavit <github@patcavit.com>
Date: Sun, 17 May 2020 08:49:37 -0700
Subject: [PATCH] WIP: Don't attempt to unsub if the iframe is destroyed
 (#4782)

Fixes #4752 by not attempting to call .removeEventListener if the iframe.contentWindow no longer exists.
---
 src/runtime/internal/dom.ts | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/runtime/internal/dom.ts b/src/runtime/internal/dom.ts
index 1823cba273..02fd3dc23e 100644
--- a/src/runtime/internal/dom.ts
+++ b/src/runtime/internal/dom.ts
@@ -270,9 +270,11 @@ export function add_resize_listener(node: HTMLElement, fn: () => void) {
 	iframe.setAttribute('aria-hidden', 'true');
 	iframe.tabIndex = -1;
 
+	const crossorigin = is_crossorigin();
+
 	let unsubscribe: () => void;
 
-	if (is_crossorigin()) {
+	if (crossorigin) {
 		iframe.src = `data:text/html,<script>onresize=function(){parent.postMessage(0,'*')}</script>`;
 		unsubscribe = listen(window, 'message', (event: MessageEvent) => {
 			if (event.source === iframe.contentWindow) fn();
@@ -287,8 +289,13 @@ export function add_resize_listener(node: HTMLElement, fn: () => void) {
 	append(node, iframe);
 
 	return () => {
+		if (crossorigin) {
+			unsubscribe();
+		} else if (unsubscribe && iframe.contentWindow) {
+			unsubscribe();
+		}
+		
 		detach(iframe);
-		if (unsubscribe) unsubscribe();
 	};
 }