From 5f925566c4f28c87fa23af9a016edc30e80cf43b Mon Sep 17 00:00:00 2001
From: Richard McSharry | Code Monkey <rmcsharry@gmail.com>
Date: Thu, 23 Oct 2025 17:02:19 +0200
Subject: [PATCH] fix: for more stable broadcast channels on CF workers (#2007)

---
 app/lib/stores/previews.ts              | 79 +++++++++++++++++--------
 app/routes/webcontainer.preview.$id.tsx | 23 ++++---
 2 files changed, 67 insertions(+), 35 deletions(-)

diff --git a/app/lib/stores/previews.ts b/app/lib/stores/previews.ts
index 710d912..74c5442 100644
--- a/app/lib/stores/previews.ts
+++ b/app/lib/stores/previews.ts
@@ -20,43 +20,47 @@ const PREVIEW_CHANNEL = 'preview-updates';
 export class PreviewsStore {
   #availablePreviews = new Map<number, PreviewInfo>();
   #webcontainer: Promise<WebContainer>;
-  #broadcastChannel: BroadcastChannel;
+  #broadcastChannel?: BroadcastChannel;
   #lastUpdate = new Map<string, number>();
   #watchedFiles = new Set<string>();
   #refreshTimeouts = new Map<string, NodeJS.Timeout>();
   #REFRESH_DELAY = 300;
-  #storageChannel: BroadcastChannel;
+  #storageChannel?: BroadcastChannel;
 
   previews = atom<PreviewInfo[]>([]);
 
   constructor(webcontainerPromise: Promise<WebContainer>) {
     this.#webcontainer = webcontainerPromise;
-    this.#broadcastChannel = new BroadcastChannel(PREVIEW_CHANNEL);
-    this.#storageChannel = new BroadcastChannel('storage-sync-channel');
+    this.#broadcastChannel = this.#maybeCreateChannel(PREVIEW_CHANNEL);
+    this.#storageChannel = this.#maybeCreateChannel('storage-sync-channel');
 
-    // Listen for preview updates from other tabs
-    this.#broadcastChannel.onmessage = (event) => {
-      const { type, previewId } = event.data;
+    if (this.#broadcastChannel) {
+      // Listen for preview updates from other tabs
+      this.#broadcastChannel.onmessage = (event) => {
+        const { type, previewId } = event.data;
 
-      if (type === 'file-change') {
-        const timestamp = event.data.timestamp;
-        const lastUpdate = this.#lastUpdate.get(previewId) || 0;
+        if (type === 'file-change') {
+          const timestamp = event.data.timestamp;
+          const lastUpdate = this.#lastUpdate.get(previewId) || 0;
 
-        if (timestamp > lastUpdate) {
-          this.#lastUpdate.set(previewId, timestamp);
-          this.refreshPreview(previewId);
+          if (timestamp > lastUpdate) {
+            this.#lastUpdate.set(previewId, timestamp);
+            this.refreshPreview(previewId);
+          }
         }
-      }
-    };
+      };
+    }
 
-    // Listen for storage sync messages
-    this.#storageChannel.onmessage = (event) => {
-      const { storage, source } = event.data;
+    if (this.#storageChannel) {
+      // Listen for storage sync messages
+      this.#storageChannel.onmessage = (event) => {
+        const { storage, source } = event.data;
 
-      if (storage && source !== this._getTabId()) {
-        this._syncStorage(storage);
-      }
-    };
+        if (storage && source !== this._getTabId()) {
+          this._syncStorage(storage);
+        }
+      };
+    }
 
     // Override localStorage setItem to catch all changes
     if (typeof window !== 'undefined') {
@@ -71,6 +75,29 @@ export class PreviewsStore {
     this.#init();
   }
 
+  #maybeCreateChannel(name: string): BroadcastChannel | undefined {
+    if (typeof globalThis === 'undefined') {
+      return undefined;
+    }
+
+    const globalBroadcastChannel = (
+      globalThis as typeof globalThis & {
+        BroadcastChannel?: typeof BroadcastChannel;
+      }
+    ).BroadcastChannel;
+
+    if (typeof globalBroadcastChannel !== 'function') {
+      return undefined;
+    }
+
+    try {
+      return new globalBroadcastChannel(name);
+    } catch (error) {
+      console.warn('[Preview] BroadcastChannel unavailable:', error);
+      return undefined;
+    }
+  }
+
   // Generate a unique ID for this tab
   private _getTabId(): string {
     if (typeof window !== 'undefined') {
@@ -130,7 +157,7 @@ export class PreviewsStore {
         }
       }
 
-      this.#storageChannel.postMessage({
+      this.#storageChannel?.postMessage({
         type: 'storage-sync',
         storage,
         source: this._getTabId(),
@@ -192,7 +219,7 @@ export class PreviewsStore {
     const timestamp = Date.now();
     this.#lastUpdate.set(previewId, timestamp);
 
-    this.#broadcastChannel.postMessage({
+    this.#broadcastChannel?.postMessage({
       type: 'state-change',
       previewId,
       timestamp,
@@ -204,7 +231,7 @@ export class PreviewsStore {
     const timestamp = Date.now();
     this.#lastUpdate.set(previewId, timestamp);
 
-    this.#broadcastChannel.postMessage({
+    this.#broadcastChannel?.postMessage({
       type: 'file-change',
       previewId,
       timestamp,
@@ -219,7 +246,7 @@ export class PreviewsStore {
       const timestamp = Date.now();
       this.#lastUpdate.set(previewId, timestamp);
 
-      this.#broadcastChannel.postMessage({
+      this.#broadcastChannel?.postMessage({
         type: 'file-change',
         previewId,
         timestamp,
diff --git a/app/routes/webcontainer.preview.$id.tsx b/app/routes/webcontainer.preview.$id.tsx
index a52ccf9..702f654 100644
--- a/app/routes/webcontainer.preview.$id.tsx
+++ b/app/routes/webcontainer.preview.$id.tsx
@@ -46,17 +46,22 @@ export default function WebContainerPreview() {
   }, [previewId, previewUrl]);
 
   useEffect(() => {
-    // Initialize broadcast channel
-    broadcastChannelRef.current = new BroadcastChannel(PREVIEW_CHANNEL);
+    const supportsBroadcastChannel = typeof window !== 'undefined' && typeof window.BroadcastChannel === 'function';
 
-    // Listen for preview updates
-    broadcastChannelRef.current.onmessage = (event) => {
-      if (event.data.previewId === previewId) {
-        if (event.data.type === 'refresh-preview' || event.data.type === 'file-change') {
-          handleRefresh();
+    if (supportsBroadcastChannel) {
+      broadcastChannelRef.current = new window.BroadcastChannel(PREVIEW_CHANNEL);
+
+      // Listen for preview updates
+      broadcastChannelRef.current.onmessage = (event) => {
+        if (event.data.previewId === previewId) {
+          if (event.data.type === 'refresh-preview' || event.data.type === 'file-change') {
+            handleRefresh();
+          }
         }
-      }
-    };
+      };
+    } else {
+      broadcastChannelRef.current = undefined;
+    }
 
     // Construct the WebContainer preview URL
     const url = `https://${previewId}.local-credentialless.webcontainer-api.io`;