# 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.

Name Type Default Description
onTopicDeleted function

callback method for topic delete event

onMessageDeliveryFailure function null

callback method for message delivery failure event

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);