fix: disconnect open realtime client after flutter web hot-restart

Author: Vinzent03

packages/supabase_flutter/lib/src/realtime_cleanup_stub.dart

@@ -0,0 +1,5 @@
+import 'package:supabase_flutter/supabase_flutter.dart';
+
+void markRealtimeClientToBeDisconnected(RealtimeClient client) {}
+
+void disconnectPreviousRealtimeClient() {}

packages/supabase_flutter/lib/src/realtime_cleanup_web.dart

@@ -0,0 +1,35 @@
+import 'dart:js_interop';
+
+import 'package:supabase_flutter/supabase_flutter.dart';
+
+@JS()
+external JSFunction? supabaseFlutterWSToClose;
+
+/// Store a function to properly disconnect the previous [RealtimeClient] in
+/// the js context.
+///
+/// WebSocket connections are not closed when Flutter is hot-restarted on web.
+///
+/// This causes old dart code that is still associated with the WebSocket
+/// connection to be still running and causes unexpected behavior like type
+/// errors and the fact that the events to the old connection may still be
+/// logged.
+void markRealtimeClientToBeDisconnected(RealtimeClient client) {
+  void disconnect() {
+    client.disconnect(
+        code: 1000, reason: 'Closed due to Flutter Web hot-restart');
+  }
+
+  supabaseFlutterWSToClose = disconnect.toJS;
+}
+
+/// Disconnect the previous [RealtimeClient] if it exists.
+///
+/// This is done by calling the function stored by
+/// [markRealtimeClientToBeDisconnected] from the js context
+void disconnectPreviousRealtimeClient() {
+  if (supabaseFlutterWSToClose != null) {
+    supabaseFlutterWSToClose!.callAsFunction();
+    supabaseFlutterWSToClose = null;
+  }
+}

packages/supabase_flutter/lib/src/supabase.dart

@@ -11,6 +11,9 @@ import 'package:supabase_flutter/src/flutter_go_true_client_options.dart';
 import 'package:supabase_flutter/src/local_storage.dart';
 import 'package:supabase_flutter/src/supabase_auth.dart';
 
+import 'realtime_cleanup_stub.dart'
+    if (dart.library.js_interop) 'realtime_cleanup_web.dart';
+
 import 'version.dart';
 
 final _log = Logger('supabase.supabase_flutter');
@@ -203,6 +206,8 @@ class Supabase with WidgetsBindingObserver {
       authOptions: authOptions,
       accessToken: accessToken,
     );
+    disconnectPreviousRealtimeClient();
+    markRealtimeClientToBeDisconnected(client.realtime);
     _widgetsBindingInstance?.addObserver(this);
     _initialized = true;
   }