fix: allow get_proxied_value to return original value when error

.changeset/afraid-penguins-battle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent dev server from throwing errors when attempting to retrieve the proxied value of an iframe's contentWindow

packages/svelte/src/internal/client/proxy.js

@@ -327,8 +327,18 @@ function update_version(signal, d = 1) {
  * @param {any} value
  */
 export function get_proxied_value(value) {
-	if (value !== null && typeof value === 'object' && STATE_SYMBOL in value) {
-		return value[STATE_SYMBOL];
+	try {
+		if (value !== null && typeof value === 'object' && STATE_SYMBOL in value) {
+			return value[STATE_SYMBOL];
+		}
+	} catch (err) {
+		// the above if check can throw an error if the value in question
+		// is the contentWindow of an iframe on another domain, in which
+		// case we want to just return the value (because it's definitely
+		// not a proxied value) so we don't break any JavaScript interacting
+		// with that iframe (such as various payment companies client side
+		// JavaScript libraries interacting with their iframes on the same
+		// domain)
 	}
 
 	return value;