---
id: client-libraries-node
title: The Pulsar Node.js client
sidebar_label: Node.js
---

The Pulsar Node.js client can be used to create Pulsar [producers](#producers), [consumers](#consumers), and [readers](#readers) in Node.js.

## Installation

You can install the [`pusar-client`](https://www.npmjs.com/package/pulsar-client) library via [npm](https://www.npmjs.com/).

### Requirements
Pulsar Node.js client library is based on the C++ client library.
Follow [these instructions](client-libraries-cpp.md#compilation) and install the Pulsar C++ client library.

### Compatibility

Compatibility between each version of the Node.js client and the C++ client is as follows:

| Node.js client | C++ client     |
| :------------- | :------------- |
| 1.0.0          | 2.3.0 or later |

If an incompatible version of the C++ client is installed, you may fail to build or run this library.

### Installation using npm

Install the `pulsar-client` library via [npm](https://www.npmjs.com/):

```shell
$ npm install pulsar-client
```

> #### Note
> 
> Also, this library works only in Node.js 10.x or later because it uses the [`node-addon-api`](https://github.com/nodejs/node-addon-api) module to wrap the C++ library.

## Connection URLs
To connect to Pulsar using client libraries, you need to specify a [Pulsar protocol](developing-binary-protocol.md) URL.

Pulsar protocol URLs are assigned to specific clusters, use the `pulsar` scheme and have a default port of 6650. Here is an example for `localhost`:

```http
pulsar://localhost:6650
```

A URL for a production Pulsar cluster may look something like this:

```http
pulsar://pulsar.us-west.example.com:6650
```

If you are using [TLS encryption](security-tls-transport.md) or [TLS Authentication](security-tls-authentication.md), the URL will look like something like this:

```http
pulsar+ssl://pulsar.us-west.example.com:6651
```

## Create a client

In order to interact with Pulsar, you will first need a client object. You can create a client instance using a `new` operator and the `Client` method, passing in a client options object (more on configuration [below](#client-configuration)).

Here is an example:

```JavaScript
const Pulsar = require('pulsar-client');

(async () => {
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });
  
  await client.close();
})();
```

### Client configuration

The following configurable parameters are available for Pulsar clients:

| Parameter | Description | Default |
| :-------- | :---------- | :------ |
| `serviceUrl` | The connection URL for the Pulsar cluster. See [above](#connection-urls) for more info. |  |
| `authentication` | Configure the authentication provider. (default: no authentication). See [TLS Authentication](security-tls-authentication.md) for more info. | |
| `operationTimeoutSeconds` | The timeout for Node.js client operations (creating producers, subscribing to and unsubscribing from [topics](reference-terminology.md#topic)). Retries will occur until this threshold is reached, at which point the operation will fail. | 30 |
| `ioThreads` | The number of threads to use for handling connections to Pulsar [brokers](reference-terminology.md#broker). | 1 |
| `messageListenerThreads` | The number of threads used by message listeners ([consumers](#consumers) and [readers](#readers)). | 1 |
| `concurrentLookupRequest` | The number of concurrent lookup requests that can be sent on each broker connection. Setting a maximum helps to keep from overloading brokers. You should set values over the default of 50000 only if the client needs to produce and/or subscribe to thousands of Pulsar topics. | 50000 |
| `tlsTrustCertsFilePath` | The file path for the trusted TLS certificate. | |
| `tlsValidateHostname` | The boolean value of setup whether to enable TLS hostname verification. | `false` |
| `tlsAllowInsecureConnection` | The boolean value of setup whether the Pulsar client accepts untrusted TLS certificate from broker. | `false` |
| `statsIntervalInSeconds` | Interval between each stat info. Stats is activated with positive statsInterval. The value should be set to 1 second at least | 600 |

## Producers

Pulsar producers publish messages to Pulsar topics. You can [configure](#producer-configuration) Node.js producers using a producer configuration object.

Here is an example:

```JavaScript
const producer = await client.createProducer({
  topic: 'my-topic',
});

await producer.send({
  data: Buffer.from("Hello, Pulsar"),
});

await producer.close();
```

> #### Promise operation
> When you create a new Pulsar producer, the operation will return `Promise` object and get producer instance or an error through executor function.  
> In this example, using await operator instead of executor function.

### Producer operations

Pulsar Node.js producers have the following methods available:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `send(Object)` | Publishes a [message](#messages) to the producer's topic. When the message is successfully acknowledged by the Pulsar broker, or an error will be thrown, the Promise object run executor function. | `Promise<null>` |
| `flush()` | Sends message from send queue to Pulser broker. When the message is successfully acknowledged by the Pulsar broker, or an error will be thrown, the Promise object run executor function. | `Promise<null>` |
| `close()` | Closes the producer and releases all resources allocated to it. If `close()` is called then no more messages will be accepted from the publisher. This method will return Promise object, and when all pending publish requests have been persisted by Pulsar then run executor function. If an error is thrown, no pending writes will be retried. | `Promise<null>` |

### Producer configuration

| Parameter | Description | Default |
| :-------- | :---------- | :------ |
| `topic` | The Pulsar [topic](reference-terminology.md#topic) to which the producer will publish messages. | |
| `producerName` | A name for the producer. If you do not explicitly assign a name, Pulsar will automatically generate a globally unique name.  If you choose to explicitly assign a name, it will need to be unique across *all* Pulsar clusters, otherwise the creation operation will throw an error. | |
| `sendTimeoutMs` | When publishing a message to a topic, the producer will wait for an acknowledgment from the responsible Pulsar [broker](reference-terminology.md#broker). If a message is not acknowledged within the threshold set by this parameter, an error will be thrown. If you set `sendTimeoutMs` to -1, the timeout will be set to infinity (and thus removed). Removing the send timeout is recommended when using Pulsar's [message de-duplication](cookbooks-deduplication.md) feature. | 30000 |
| `initialSequenceId` | The initial sequence ID of the message. When producer send message, add sequence ID to message. The ID is increased each time to send. | |
| `maxPendingMessages` | The maximum size of the queue holding pending messages (i.e. messages waiting to receive an acknowledgment from the [broker](reference-terminology.md#broker)). By default, when the queue is full all calls to the `send` method will fail *unless* `blockIfQueueFull` is set to `true`. | 1000 |
| `maxPendingMessagesAcrossPartitions` | The maximum size of the sum of partition's  pending queue. | 50000 |
| `blockIfQueueFull` | If set to `true`, the producer's `send` method will wait when the outgoing message queue is full rather than failing and throwing an error (the size of that queue is dictated by the `maxPendingMessages` parameter); if set to `false` (the default), `send` operations will fail and throw a error when the queue is full. | `false` |
| `messageRoutingMode` | The message routing logic (for producers on [partitioned topics](concepts-messaging.md#partitioned-topics)). This logic is applied only when no key is set on messages. The available options are: round robin (`RoundRobinDistribution`), or publishing all messages to a single partition (`UseSinglePartition`, the default). | `UseSinglePartition` |
| `hashingScheme` | The hashing function that determines the partition on which a particular message is published (partitioned topics only). The available options are: `JavaStringHash` (the equivalent of `String.hashCode()` in Java), `Murmur3_32Hash` (applies the [Murmur3](https://en.wikipedia.org/wiki/MurmurHash) hashing function), or `BoostHash` (applies the hashing function from C++'s [Boost](https://www.boost.org/doc/libs/1_62_0/doc/html/hash.html) library). | `BoostHash` |
| `compressionType` | The message data compression type used by the producer. The available options are [`LZ4`](https://github.com/lz4/lz4), and [`Zlib`](https://zlib.net/). | Compression None |
| `batchingEnabled` | If set to `true`, the producer send message as batch. | `true` |
| `batchingMaxPublishDelayMs` | The maximum time of delay sending message in batching. | 10 |
| `batchingMaxMessages` | The maximum size of sending message in each time of batching. | 1000 |
| `properties` | The metadata of producer. | |

### Producer example

This example creates a Node.js producer for the `my-topic` topic and sends 10 messages to that topic:

```JavaScript
const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });

  // Create a producer
  const producer = await client.createProducer({
    topic: 'my-topic',
  });

  // Send messages
  for (let i = 0; i < 10; i += 1) {
    const msg = `my-message-${i}`;
    producer.send({
      data: Buffer.from(msg),
    });
    console.log(`Sent message: ${msg}`);
  }
  await producer.flush();

  await producer.close();
  await client.close();
})();
```

## Consumers

Pulsar consumers subscribe to one or more Pulsar topics and listen for incoming messages produced on that topic/those topics. You can [configure](#consumer-configuration) Node.js consumers using a consumer configuration object.

Here is an example:

```JavaScript
const consumer = await client.subscribe({
  topic: 'my-topic',
  subscription: 'my-subscription',
});

const msg = await consumer.receive();
console.log(msg.getData().toString());
consumer.acknowledge(msg);

await consumer.close();
```

> #### Promise operation
> When you create a new Pulsar consumer, the operation will return `Promise` object and get consumer instance or an error through executor function.  
> In this example, using await operator instead of executor function.

### Consumer operations

Pulsar Node.js consumers have the following methods available:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `receive()` | Receives a single message from the topic. When the message is available, the Promise object run executor function and get message object. | `Promise<Object>` |
| `receive(Number)` | Receives a single message from the topic with specific timeout in milliseconds. | `Promise<Object>` |
| `acknowledge(Object)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) a message to the Pulsar [broker](reference-terminology.md#broker) by message object. | `void` |
| `acknowledgeId(Object)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) a message to the Pulsar [broker](reference-terminology.md#broker) by message ID object. | `void` |
| `acknowledgeCumulative(Object)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) *all* the messages in the stream, up to and including the specified message. The `acknowledgeCumulative` method will return void, and send the ack to the broker asynchronously. After that, the messages will *not* be redelivered to the consumer. Cumulative acking can not be used with a [shared](concepts-messaging.md#shared) subscription type. | `void` |
| `acknowledgeCumulativeId(Object)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) *all* the messages in the stream, up to and including the specified message ID. | `void` |
| `close()` | Closes the consumer, disabling its ability to receive messages from the broker. | `Promise<null>` |

### Consumer configuration

| Parameter | Description | Default |
| :-------- | :---------- | :------ |
| `topic` | The Pulsar [topic](reference-terminology.md#topic) on which the consumer will establish a subscription and listen for messages. | |
| `subscription` | The subscription name for this consumer. | |
| `subscriptionType` | Available options are `Exclusive`, `Shared`, and `Failover`. | `Exclusive` |
| `ackTimeoutMs` | Acknowledge timeout in milliseconds. | 0 |
| `receiverQueueSize` | Sets the size of the consumer's receiver queue, i.e. the number of messages that can be accumulated by the consumer before the application calls `receive`. A value higher than the default of 1000 could increase consumer throughput, though at the expense of more memory utilization. | 1000 |
| `receiverQueueSizeAcrossPartitions` | Set the max total receiver queue size across partitions. This setting will be used to reduce the receiver queue size for individual partitions if the total exceeds this value. | 50000 |
| `consumerName` | The name of consumer. Currently(v2.4.1), [failover](concepts-messaging.md#failover) mode use consumer name in ordering. | |
| `properties` | The metadata of consumer. | |

### Consumer example

This example creates a Node.js consumer with the `my-subscription` subscription on the `my-topic` topic, receives messages, prints the content that arrive, and acknowledges each message to the Pulsar broker for 10 times:

```JavaScript
const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
  });

  // Create a consumer
  const consumer = await client.subscribe({
    topic: 'my-topic',
    subscription: 'my-subscription',
    subscriptionType: 'Exclusive',
  });

  // Receive messages
  for (let i = 0; i < 10; i += 1) {
    const msg = await consumer.receive();
    console.log(msg.getData().toString());
    consumer.acknowledge(msg);
  }

  await consumer.close();
  await client.close();
})();
```

## Readers

Pulsar readers process messages from Pulsar topics. Readers are different from consumers because with readers you need to explicitly specify which message in the stream you want to begin with (consumers, on the other hand, automatically begin with the most recently unacked message). You can [configure](#reader-configuration) Node.js readers using a reader configuration object.

Here is an example:

```JavaScript
const reader = await client.createReader({
  topic: 'my-topic',
  startMessageId: Pulsar.MessageId.earliest(),
});

const msg = await reader.readNext();
console.log(msg.getData().toString());

await reader.close();
```

### Reader operations

Pulsar Node.js readers have the following methods available:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `readNext()` | Receives the next message on the topic (analogous to the `receive` method for [consumers](#consumer-operations)). When the message is available, the Promise object run executor function and get message object. | `Promise<Object>` |
| `readNext(Number)` | Receives a single message from the topic with specific timeout in milliseconds. | `Promise<Object>` |
| `hasNext()` | Return whether Proker has next message in target topic. | `Boolean` |
| `close()` | Closes the reader, disabling its ability to receive messages from the broker. | `Promise<null>` |

### Reader configuration

| Parameter | Description | Default |
| :-------- | :---------- | :------ |
| `topic` | The Pulsar [topic](reference-terminology.md#topic) on which the reader will establish a subscription and listen for messages. | |
| `startMessageId` | The initial reader position, i.e. the message at which the reader begins processing messages. The options are `Pulsar.MessageId.earliest` (the earliest available message on the topic), `Pulsar.MessageId.latest` (the latest available message on the topic), or a message ID object for a position that is not earliest or latest. | |
| `receiverQueueSize` | Sets the size of the reader's receiver queue, i.e. the number of messages that can be accumulated by the reader before the application calls `readNext`. A value higher than the default of 1000 could increase reader throughput, though at the expense of more memory utilization. | 1000 |
| `readerName` | The name of the reader. |  |
| `subscriptionRolePrefix` | The subscription role prefix. | |

### Reader example

This example creates a Node.js reader with the `my-topic` topic, reads messages, and prints the content that arrive for 10 times:

```JavaScript
const Pulsar = require('pulsar-client');

(async () => {
  // Create a client
  const client = new Pulsar.Client({
    serviceUrl: 'pulsar://localhost:6650',
    operationTimeoutSeconds: 30,
  });

  // Create a reader
  const reader = await client.createReader({
    topic: 'my-topic',
    startMessageId: Pulsar.MessageId.earliest(),
  });

  // read messages
  for (let i = 0; i < 10; i += 1) {
    const msg = await reader.readNext();
    console.log(msg.getData().toString());
  }

  await reader.close();
  await client.close();
})();
```

## Messages

In Pulsar Node.js client, you have to construct producer message object for producer.

Here is an example message:

```JavaScript
const msg = {
  data: Buffer.from('Hello, Pulsar'),
  partitionKey: 'key1',
  properties: {
    'foo': 'bar',
  },
  eventTimestamp: Date.now(),
  replicationClusters: [
    'cluster1',
    'cluster2',
  ],
}

await producer.send(msg);
```

The following keys are available for producer message objects:

| Parameter | Description |
| :-------- | :---------- |
| `data` | The actual data payload of the message. |
| `properties` | A Object for any application-specific metadata attached to the message. |
| `eventTimestamp` | The timestamp associated with the message. |
| `sequenceId` | The sequence ID of the message. |
| `partitionKey` | The optional key associated with the message (particularly useful for things like topic compaction). |
| `replicationClusters` | The clusters to which this message will be replicated. Pulsar brokers handle message replication automatically; you should only change this setting if you want to override the broker default. |

### Message object operations

In Pulsar Node.js client, you can receive (or read) message object as consumer (or reader).

The message object have the following methods available:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `getTopicName()` | Getter method of topic name. | `String` |
| `getProperties()` | Getter method of properties. | `Array<Object>` |
| `getData()` | Getter method of message data. | `Buffer` |
| `getMessageId()` | Getter method of [message id object](#message-id-object-operations). | `Object` |
| `getPublishTimestamp()` | Getter method of publish timestamp. | `Number` |
| `getEventTimestamp()` | Getter method of event timestamp. | `Number` |
| `getPartitionKey()` | Getter method of partition key. | `String` |

### Message ID object operations

In Pulsar Node.js client, you can get message id object from message object.

The message id object have the following methods available:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `serialize()` | Serialize the message id into a Buffer for storing. | `Buffer` |
| `toString()` | Get message id as String. | `String` |

The client has static method of message id object. You can access it as `Pulsar.MessageId.someStaticMethod` too.

The following static methods are available for the message id object:

| Method | Description | Return type |
| :----- | :---------- | :---------- |
| `earliest()` | MessageId representing the earliest, or oldest available message stored in the topic. | `Object` |
| `latest()` | MessageId representing the latest, or last published message in the topic. | `Object` |
| `deserialize(Buffer)` | Deserialize a message id object from a Buffer. | `Object` |

