How to use Google PubSub without Cloud Function

Question

How can I use Google PubSub to retrieve billing updates without using cloud functions? I am using the code below currently but it says that onPublish does not exist:

const { PubSub } = require('@google-cloud/pubsub');
const pubsub = new PubSub('MyProjectID');



handleServerEvent = pubsub.topic(GOOGLE_PLAY_PUBSUB_BILLING_TOPIC)
  .onPublish(async (message) => {

  })

TypeError: pubsub.topic(...).onPublish is not a function

I am using Node.js and want to react to events published on a topic.

Answer 1

The onPublish() method is a part of Cloud Functions API. You need to use createSubscription() to get a Subscription object and then use it to listen for new messages. Try the following:

const listenToTopic = async (topicName: string) => {
  const [sub] = await pubsub
    .topic(topicName)
    .createSubscription("subscriptionName");

  sub.on("message", (message) => {
    message.ack();
    console.log(`Received message: ${message}`);  
  });
};

// start listener
listenToTopic(GOOGLE_PLAY_PUBSUB_BILLING_TOPIC)

After creating the subscription once you need to change createSubscription("subscriptionName") to subscription("subscriptionName") to listen to incoming messages as the subscription has been created already