Class Topic (3.7.5)

A Topic object allows you to interact with a Cloud Pub/Sub topic.

Package

Examples


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

const topic = pubsub.topic('my-topic');

To enable message ordering, set enableMessageOrdering to true. Please note that this does not persist to an actual topic.


const topic = pubsub.topic('ordered-topic', {enableMessageOrdering: true});

Constructors

(constructor)(pubsub, name, options)

constructor(pubsub: PubSub, name: string, options?: PublishOptions);

Constructs a new instance of the Topic class

Parameters
Name	Description
`pubsub`	`PubSub`
`name`	`string`
`options`	`PublishOptions`

Properties

getSubscriptionsStream

getSubscriptionsStream: () => ObjectStream<Subscription>;

iam

iam: IAM;

metadata

metadata?: TopicMetadata;

name

name: string;

parent

parent: PubSub;

publisher

publisher: Publisher;

pubsub

pubsub: PubSub;

request

request: typeof PubSub.prototype.request;

Methods

create(gaxOpts)

create(gaxOpts?: CallOptions): Promise<CreateTopicResponse>;

Create a topic.

Parameter
Name	Description
`gaxOpts`	`CallOptions` Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/interfaces/CallOptions.html.

Returns

Type Description

Promise<CreateTopicResponse>

{Promise

Example


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

const topic = pubsub.topic('my-topic');

topic.create((err, topic, apiResponse) => {
  if (!err) {
    // The topic was created successfully.
  }
});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.create().then((data) => {
  const topic = data[0];
  const apiResponse = data[1];
});

create(callback)

create(callback: CreateTopicCallback): void;

Parameter
Name	Description
`callback`	`CreateTopicCallback`

Returns
Type	Description
`void`

create(gaxOpts, callback)

create(gaxOpts: CallOptions, callback: CreateTopicCallback): void;

Parameters
Name	Description
`gaxOpts`	`CallOptions`
`callback`	`CreateTopicCallback`

Returns
Type	Description
`void`

createSubscription(name, callback)

createSubscription(name: string, callback: CreateSubscriptionCallback): void;

Create a subscription to this topic.

Parameters
Name	Description
`name`	`string` The name of the subscription.
`callback`	`CreateSubscriptionCallback` Callback function.

Returns

Type Description

void

{Promise

Example


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

const topic = pubsub.topic('my-topic');
const callback = function(err, subscription, apiResponse) {};

// Without specifying any options.
topic.createSubscription('newMessages', callback);

// With options.
topic.createSubscription('newMessages', {
  ackDeadlineSeconds: 90
}, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.createSubscription('newMessages').then((data) => {
  const subscription = data[0];
  const apiResponse = data[1];
});

createSubscription(name, options)

createSubscription(name: string, options?: CreateSubscriptionOptions): Promise<CreateSubscriptionResponse>;

Parameters
Name	Description
`name`	`string`
`options`	`CreateSubscriptionOptions`

Returns
Type	Description
`Promise<CreateSubscriptionResponse>`

createSubscription(name, options, callback)

createSubscription(name: string, options: CreateSubscriptionOptions, callback: CreateSubscriptionCallback): void;

Parameters
Name	Description
`name`	`string`
`options`	`CreateSubscriptionOptions`
`callback`	`CreateSubscriptionCallback`

Returns
Type	Description
`void`

delete(callback)

delete(callback: EmptyCallback): void;

Delete the topic. This will not delete subscriptions to this topic.

Parameter
Name	Description
`callback`	`EmptyCallback` The callback function.

Returns
Type	Description
`void`

Example


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

const topic = pubsub.topic('my-topic');

topic.delete((err, apiResponse) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.delete().then((data) => {
  const apiResponse = data[0];
});

delete(gaxOpts)

delete(gaxOpts?: CallOptions): Promise<EmptyResponse>;

Parameter
Name	Description
`gaxOpts`	`CallOptions`

Returns
Type	Description
`Promise<EmptyResponse>`

delete(gaxOpts, callback)

delete(gaxOpts: CallOptions, callback: EmptyCallback): void;

Parameters
Name	Description
`gaxOpts`	`CallOptions`
`callback`	`EmptyCallback`

Returns
Type	Description
`void`

exists()

exists(): Promise<ExistsResponse>;

Check if a topic exists.

Returns

Type Description

Promise<ExistsResponse>

{Promise

Example


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

const topic = pubsub.topic('my-topic');

topic.exists((err, exists) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.exists().then((data) => {
  const exists = data[0];
});

exists(callback)

exists(callback: ExistsCallback): void;

Parameter
Name	Description
`callback`	`ExistsCallback`

Returns
Type	Description
`void`

flowControlled()

flowControlled(): FlowControlledPublisher;

Creates a FlowControlledPublisher for this Topic.

FlowControlledPublisher is a helper that lets you control how many messages are simultaneously queued to send, to avoid ballooning memory usage on a low bandwidth connection to Pub/Sub.

Note that it's perfectly fine to create more than one on the same Topic. The actual flow control settings on the Topic will apply across all FlowControlledPublisher objects on that Topic.

Returns
Type	Description
`FlowControlledPublisher`	{FlowControlledPublisher} The flow control helper.

flush()

flush(): Promise<void>;

Immediately sends all remaining queued data. This is mostly useful if you are planning to call close() on the PubSub object that holds the server connections.

Returns

Type Description

Promise<void>

{Promise

flush(callback)

flush(callback: EmptyCallback): void;

Parameter
Name	Description
`callback`	`EmptyCallback`

Returns
Type	Description
`void`

formatName_(projectId, name)

static formatName_(projectId: string, name: string): string;

Format the name of a topic. A Topic's full name is in the format of 'projects/{projectId}/topics/{topicName}'.

{string}

Parameters
Name	Description
`projectId`	`string`
`name`	`string`

Returns
Type	Description
`string`

get(callback)

get(callback: GetTopicCallback): void;

Get a topic if it exists.

Parameter
Name	Description
`callback`	`GetTopicCallback` Callback function.

Returns

Type Description

void

{Promise

Example


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

const topic = pubsub.topic('my-topic');

topic.get((err, topic, apiResponse) => {
  // The `topic` data has been populated.
});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.get().then((data) => {
  const topic = data[0];
  const apiResponse = data[1];
});

get(gaxOpts)

get(gaxOpts?: GetTopicOptions): Promise<GetTopicResponse>;

Parameter
Name	Description
`gaxOpts`	`GetTopicOptions`

Returns
Type	Description
`Promise<GetTopicResponse>`

get(gaxOpts, callback)

get(gaxOpts: GetTopicOptions, callback: GetTopicCallback): void;

Parameters
Name	Description
`gaxOpts`	`GetTopicOptions`
`callback`	`GetTopicCallback`

Returns
Type	Description
`void`

getMetadata(callback)

getMetadata(callback: GetTopicMetadataCallback): void;

Get the official representation of this topic from the API.

Parameter
Name	Description
`callback`	`GetTopicMetadataCallback` Callback function.

Returns

Type Description

void

{Promise

Example


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

const topic = pubsub.topic('my-topic');

topic.getMetadata((err, apiResponse) => {});

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.getMetadata().then((data) => {
  const apiResponse = data[0];
});

getMetadata(gaxOpts, callback)

getMetadata(gaxOpts: CallOptions, callback: GetTopicMetadataCallback): void;

Parameters
Name	Description
`gaxOpts`	`CallOptions`
`callback`	`GetTopicMetadataCallback`

Returns
Type	Description
`void`

getMetadata(gaxOpts)

getMetadata(gaxOpts?: CallOptions): Promise<GetTopicMetadataResponse>;

Parameter
Name	Description
`gaxOpts`	`CallOptions`

Returns
Type	Description
`Promise<GetTopicMetadataResponse>`

getPublishOptionDefaults()

getPublishOptionDefaults(): PublishOptions;

Get the default publisher options. These may be modified and passed back into .

Returns
Type	Description
`PublishOptions`

Example


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

const topic = pubsub.topic('my-topic');

const defaults = topic.getPublishOptionDefaults();
defaults.batching.maxMilliseconds = 10;
topic.setPublishOptions(defaults);

getSubscriptions(callback)

getSubscriptions(callback: GetTopicSubscriptionsCallback): void;

Get a list of the subscriptions registered to this topic. You may optionally provide a query object as the first argument to customize the response.

Your provided callback will be invoked with an error object if an API error occurred or an array of {module:pubsub/subscription} objects.

Parameter
Name	Description
`callback`	`GetTopicSubscriptionsCallback` Callback function.

Returns

Type Description

void

{Promise

Example


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

const topic = pubsub.topic('my-topic');

topic.getSubscriptions((err, subscriptions) => {
  // subscriptions is an array of `Subscription` objects.
});

// Customize the query.
topic.getSubscriptions({
  pageSize: 3
}, callback);

//-
// If the callback is omitted, we'll return a Promise.
//-
topic.getSubscriptions().then((data) => {
  const subscriptions = data[0];
});

getSubscriptions(options, callback)

getSubscriptions(options: PageOptions, callback: GetTopicSubscriptionsCallback): void;

Parameters
Name	Description
`options`	`PageOptions`
`callback`	`GetTopicSubscriptionsCallback`

Returns
Type	Description
`void`

getSubscriptions(options)

getSubscriptions(options?: PageOptions): Promise<GetTopicSubscriptionsResponse>;

Parameter
Name	Description
`options`	`PageOptions`

Returns
Type	Description
`Promise<GetTopicSubscriptionsResponse>`

publish(data, attributes)

publish(data: Buffer, attributes?: Attributes): Promise<string>;

Publish the provided message.

Parameters
Name	Description
`data`	`Buffer` The message data. This must come in the form of a Buffer object.
`attributes`	`Attributes` Attributes for this message.

Returns

Type Description

Promise<string>

{Promise

Examples


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

const topic = pubsub.topic('my-topic');
const data = Buffer.from('Hello, world!');

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publish(data, callback);

Optionally you can provide an object containing attributes for the message. Note that all values in the object must be strings.


const attributes = {
  key: 'value'
};

topic.publish(data, attributes, callback);

If the callback is omitted, we'll return a Promise.


topic.publish(data).then((messageId) => {});

publish(data, callback)

publish(data: Buffer, callback: PublishCallback): void;

Parameters
Name	Description
`data`	`Buffer`
`callback`	`PublishCallback`

Returns
Type	Description
`void`

publish(data, attributes, callback)

publish(data: Buffer, attributes: Attributes, callback: PublishCallback): void;

Parameters
Name	Description
`data`	`Buffer`
`attributes`	`Attributes`
`callback`	`PublishCallback`

Returns
Type	Description
`void`

publishJSON(json, attributes)

publishJSON(json: object, attributes?: Attributes): Promise<string>;

Publish the provided JSON. It should be noted that all messages published are done so in the form of a Buffer. This is simply a convenience method that will transform JSON into a Buffer before publishing. Subscription objects will always return message data in the form of a Buffer, so any JSON published will require manual deserialization.

Parameters
Name	Description
`json`	`object` The JSON data to publish.
`attributes`	`Attributes` Attributes for this message.

Returns

Type Description

Promise<string>

{Promise

Examples


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

const data = {
  foo: 'bar'
};

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publishJSON(data, callback);

Optionally you can provide an object containing attributes for the message. Note that all values in the object must be strings.


const attributes = {
  key: 'value'
};

topic.publishJSON(data, attributes, callback);

If the callback is omitted, we'll return a Promise.


topic.publishJSON(data).then((messageId) => {});

publishJSON(json, callback)

publishJSON(json: object, callback: PublishCallback): void;

Parameters
Name	Description
`json`	`object`
`callback`	`PublishCallback`

Returns
Type	Description
`void`

publishJSON(json, attributes, callback)

publishJSON(json: object, attributes: Attributes, callback: PublishCallback): void;

Parameters
Name	Description
`json`	`object`
`attributes`	`Attributes`
`callback`	`PublishCallback`

Returns
Type	Description
`void`

publishMessage(message)

publishMessage(message: MessageOptions): Promise<string>;

Publish the provided message.

Parameter
Name	Description
`message`	`MessageOptions` Message object.

Returns

Type Description

Promise<string>

{Promise

Examples


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

const data = Buffer.from('Hello, world!');

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publishMessage({data}, callback);

Publish JSON message data.


const json = {foo: 'bar'};

topic.publishMessage({json}, callback);

To publish messages in order (this is still experimental), make sure message ordering is enabled and provide an ordering key


const topic = pubsub.topic('ordered-topic', {messageOrdering: true});
const orderingKey = 'my-key';

topic.publishMessage({data, orderingKey}, callback);

If the callback is omitted, we'll return a Promise.


const messageId = await topic.publishMessage({data});

publishMessage(message, callback)

publishMessage(message: MessageOptions, callback: PublishCallback): void;

Parameters
Name	Description
`message`	`MessageOptions`
`callback`	`PublishCallback`

Returns
Type	Description
`void`

resumePublishing(orderingKey)

resumePublishing(orderingKey: string): void;

In the event that the client fails to publish an ordered message, all subsequent publish calls using the same ordering key will fail. Calling this method will disregard the publish failure, allowing the supplied ordering key to be used again in the future.

Parameter
Name	Description
`orderingKey`	`string` The ordering key in question.

Returns
Type	Description
`void`

Example


const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic', {messageOrdering: true});

const orderingKey = 'foo';
const data = Buffer.from('Hello, order!');

topic.publishMessage({data, orderingKey}, err => {
  if (err) {
    topic.resumePublishing(orderingKey);
  }
});

setMetadata(options, gaxOpts)

setMetadata(options: TopicMetadata, gaxOpts?: CallOptions): Promise<SetTopicMetadataResponse>;

Updates the topic.

Parameters
Name	Description
`options`	`TopicMetadata`
`gaxOpts`	`CallOptions` Request configuration options, outlined here: https://googleapis.github.io/gax-nodejs/interfaces/CallOptions.html.

Returns

Type Description

Promise<SetTopicMetadataResponse>

{Promise

Examples


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

const topic = pubsub.topic('my-topic');
const metadata = {
  labels: {foo: 'bar'}
};

topic.setMetadata(metadata, err => {
  if (err) {
    // Error handling omitted.
  }
});

If the callback is omitted, we'll return a Promise.


topic.setMetadata(metadata).then((data) => {
  const apiResponse = data[0];
});

setMetadata(options, callback)

setMetadata(options: TopicMetadata, callback: SetTopicMetadataCallback): void;

Parameters
Name	Description
`options`	`TopicMetadata`
`callback`	`SetTopicMetadataCallback`

Returns
Type	Description
`void`

setMetadata(options, gaxOpts, callback)

setMetadata(options: TopicMetadata, gaxOpts: CallOptions, callback: SetTopicMetadataCallback): void;

Parameters
Name	Description
`options`	`TopicMetadata`
`gaxOpts`	`CallOptions`
`callback`	`SetTopicMetadataCallback`

Returns
Type	Description
`void`

setPublishOptions(options)

setPublishOptions(options: PublishOptions): void;

Set the publisher options.

Parameter
Name	Description
`options`	`PublishOptions` The publisher options.

Returns
Type	Description
`void`

Example


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

const topic = pubsub.topic('my-topic');

topic.setPublishOptions({
  batching: {
    maxMilliseconds: 10
  }
});

subscription(name, options)

subscription(name: string, options?: SubscriptionOptions): Subscription;

Create a Subscription object. This command by itself will not run any API requests. You will receive a {module:pubsub/subscription} object, which will allow you to interact with a subscription.

Parameters
Name	Description
`name`	`string` Name of the subscription.
`options`	`SubscriptionOptions` Configuration object. {Subscription}

Returns
Type	Description
`Subscription`

Example


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

const topic = pubsub.topic('my-topic');
const subscription = topic.subscription('my-subscription');

// Register a listener for `message` events.
subscription.on('message', (message) => {
  // Called every time a message is received.
  // message.id = ID of the message.
  // message.ackId = ID used to acknowledge the message receival.
  // message.data = Contents of the message.
  // message.attributes = Attributes of the message.
  // message.publishTime = Timestamp when Pub/Sub received the message.
});