emit instead of throw async error

src/client.ts

@@ -462,7 +462,7 @@ export class SubscriptionClient {
         try {
           JSON.parse(serializedMessage);
         } catch (e) {
-          throw new Error(`Message must be JSON-serializable. Got: ${message}`);
+          this.eventEmitter.emit('error', new Error(`Message must be JSON-serializable. Got: ${message}`));
         }
 
         this.client.send(serializedMessage);
@@ -473,8 +473,8 @@ export class SubscriptionClient {
         break;
       default:
         if (!this.reconnecting) {
-          throw new Error('A message was not sent because socket is not connected, is closing or ' +
-            'is already closed. Message was: ' + JSON.stringify(message));
+          this.eventEmitter.emit('error', new Error('A message was not sent because socket is not connected, is closing or ' +
+            'is already closed. Message was: ' + JSON.stringify(message)));
         }
     }
   }

src/test/tests.ts

@@ -1078,21 +1078,26 @@ describe('Client', function () {
     wsServer.on('connection', (connection: WebSocket) => {
       connection.close();
     });
-
+    let errorCount = 0;
     const subscriptionsClient = new SubscriptionClient(`ws://localhost:${RAW_TEST_PORT}/`, {
       timeout: 500,
       reconnect: true,
       reconnectionAttempts: 2,
     });
+    subscriptionsClient.onError((error) => {
+      expect(error.message).to.contain('A message was not sent');
+      errorCount += 1;
+    });
     const connectSpy = sinon.spy(subscriptionsClient as any, 'connect');
 
     setTimeout(() => {
       expect(connectSpy.callCount).to.be.equal(2);
+      expect(errorCount).to.be.equal(1);
       done();
     }, 1500);
   });
 
-  it('should stop trying to reconnect to the server if it not receives the ack', function (done) {
+  it('should stop trying to reconnect to the server if it does not receives the ack', function (done) {
     const subscriptionsClient = new SubscriptionClient(`ws://localhost:${RAW_TEST_PORT}/`, {
       timeout: 500,
       reconnect: true,