# new TopicListener(onTopicDeleted, onMessageDeliveryFailure)
In case a topic is deleted, it is a forceful deletion and deletes all messages and related meta-info form the cache. Hence, the subscriber and publisher must be notified of this deletion through TopicDeleteCallback method for notifying application about topic deletion.
Parameters:
| Name | Type | Default | Description |
|---|---|---|---|
onTopicDeleted |
function | callback method for topic delete event |
|
onMessageDeliveryFailure |
function | null | callback method for message delivery failure event |
Example
const ncache = require('ncache-client'); function onTopicDeleted(sender, args) { //... } function onMessageDeliveryFailure(sender, args) { //.. } //Initialize the Cache Cluster let cache = await ncache.CacheManager.getCache("demoCache"); //Get messaging service from cache. let messagingService = await cache.getMessagingService(); //Create topic from messaging service . let createdTopic = await messagingService.createTopic("mytopic"); //Register for topic deletion events or message delivery failure. let topicListener = new ncache.TopicListener(onTopicDeleted, onMessageDeliveryFailure); await createdTopic.addTopicDeletedListener(topicListener); await createdTopic.addMessageDeliveryFailureListener(topicListener);