From 2ff8fe12e7717dde036d2e9d41b9e2393b7a66f2 Mon Sep 17 00:00:00 2001
From: Luciano Vernaschi <luciano@vaadin.com>
Date: Tue, 10 Dec 2024 15:55:58 +0100
Subject: [PATCH] Add error message parameter to `onError` callback in
 subscription

---
 packages/ts/frontend/src/Connect.ts              | 2 +-
 packages/ts/frontend/src/FluxConnection.ts       | 6 +++---
 packages/ts/frontend/test/FluxConnection.test.ts | 1 +
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/packages/ts/frontend/src/Connect.ts b/packages/ts/frontend/src/Connect.ts
index 2ded276983..5609e63bef 100644
--- a/packages/ts/frontend/src/Connect.ts
+++ b/packages/ts/frontend/src/Connect.ts
@@ -42,7 +42,7 @@ export interface Subscription<T> {
   onComplete(callback: () => void): Subscription<T>;
 
   /** Called when an exception occured in the subscription. */
-  onError(callback: () => void): Subscription<T>;
+  onError(callback: (message: string) => void): Subscription<T>;
 
   /** Called when a new value is available. */
   onNext(callback: (value: T) => void): Subscription<T>;
diff --git a/packages/ts/frontend/src/FluxConnection.ts b/packages/ts/frontend/src/FluxConnection.ts
index bc17784861..a0cc022b79 100644
--- a/packages/ts/frontend/src/FluxConnection.ts
+++ b/packages/ts/frontend/src/FluxConnection.ts
@@ -80,7 +80,7 @@ export class FluxConnection extends EventTarget {
   readonly #endpointInfos = new Map<string, EndpointInfo>();
   #nextId = 0;
   readonly #onCompleteCallbacks = new Map<string, () => void>();
-  readonly #onErrorCallbacks = new Map<string, () => void>();
+  readonly #onErrorCallbacks = new Map<string, (message: string) => void>();
   readonly #onNextCallbacks = new Map<string, (value: any) => void>();
   readonly #onStateChangeCallbacks = new Map<string, (event: FluxSubscriptionStateChangeEvent) => void>();
   readonly #statusOfSubscriptions = new Map<string, FluxSubscriptionState>();
@@ -154,7 +154,7 @@ export class FluxConnection extends EventTarget {
         this.#onCompleteCallbacks.set(id, callback);
         return hillaSubscription;
       },
-      onError: (callback: () => void): Subscription<any> => {
+      onError: (callback: (message: string) => void): Subscription<any> => {
         this.#onErrorCallbacks.set(id, callback);
         return hillaSubscription;
       },
@@ -285,7 +285,7 @@ export class FluxConnection extends EventTarget {
       } else {
         const callback = this.#onErrorCallbacks.get(id);
         if (callback) {
-          callback();
+          callback(message.message);
         }
         this.#removeSubscription(id);
         if (!callback) {
diff --git a/packages/ts/frontend/test/FluxConnection.test.ts b/packages/ts/frontend/test/FluxConnection.test.ts
index 2fdd08cfdd..c6005a55ac 100644
--- a/packages/ts/frontend/test/FluxConnection.test.ts
+++ b/packages/ts/frontend/test/FluxConnection.test.ts
@@ -125,6 +125,7 @@ describe('@vaadin/hilla-frontend', () => {
       const msg: ClientErrorMessage = { '@type': 'error', id: '0', message: 'it failed' };
       emitMessage(msg);
       expect(onError).to.have.been.calledOnce;
+      expect(onError).to.have.been.calledWith('it failed');
     });
 
     it('should not deliver messages after completing', () => {