fix: don't let a listener exception wedge EventEmitter

src/cdp/connection.ts

@@ -105,9 +105,12 @@ export default class Connection {
     if (!session) {
       const disposedDate = this._disposedSessions.get(object.sessionId);
       if (!disposedDate) {
-        throw new Error(
-          `Unknown session id: ${object.sessionId} while processing: ${object.method}`,
+        this.logger.warn(
+          LogTag.Internal,
+          'Got message for an unknown session',
+          { sessionId: object.sessionId, method: object.method },
         );
+        return; // We just ignore messages for unknown sessions
       } else {
         const secondsAgo = (Date.now() - disposedDate.getTime()) / 1000.0;
         this.logger.warn(

src/common/events.test.ts

@@ -0,0 +1,27 @@
+/*---------------------------------------------------------
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ *--------------------------------------------------------*/
+
+import { expect } from 'chai';
+import { EventEmitter } from './events';
+
+describe('EventEmitter', () => {
+  it('keeps delivering events after a listener throws', () => {
+    const emitter = new EventEmitter<string>();
+    const delivered: string[] = [];
+
+    emitter.event(event => {
+      if (event === 'throws') {
+        throw new Error('listener error');
+      }
+
+      delivered.push(event);
+    });
+
+    emitter.fire('before');
+    expect(() => emitter.fire('throws')).to.throw('listener error');
+    emitter.fire('after');
+
+    expect(delivered).to.deep.equal(['before', 'after']);
+  });
+});

src/common/events.ts

@@ -57,11 +57,14 @@ export class EventEmitter<T> implements IDisposable {
     if (!this._deliveryQueue) this._deliveryQueue = [];
     for (const data of this._listeners) this._deliveryQueue.push({ data, event });
     if (!dispatch) return;
-    for (let index = 0; index < this._deliveryQueue.length; index++) {
-      const { data, event } = this._deliveryQueue[index];
-      data.listener.call(data.thisArg, event);
+    try {
+      for (let index = 0; index < this._deliveryQueue.length; index++) {
+        const { data, event } = this._deliveryQueue[index];
+        data.listener.call(data.thisArg, event);
+      }
+    } finally {
+      this._deliveryQueue = undefined;
     }
-    this._deliveryQueue = undefined;
   }
 
   dispose() {