interface instead of type

dist/mqttclient.js

@@ -26,6 +26,9 @@ class MqttClient {
             for (let topicHandler of this._topicHandlers) {
                 if (this.topicMatch(topicHandler.topic, topic)) {
                     log.info(`received topic ${topic} matches registered topic ${topicHandler.topic}`);
+                    if (topicHandler.callback != null) {
+                        topicHandler.callback(payload);
+                    }
                 }
             }
         });