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1.1.2 • Public • Published

TypeScript NATS - Node.js Client

A TypeScript Node.js client for the NATS messaging system.

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ts-nats is a typescript nats library for node that supports Promises and async/await patterns. Full documentation.


npm install ts-nats

Basic Usage

The starting point is the connect() function. You can give no arguments, a port, an URL or a NatsConnectionOption specifying detailed behaviour. Inside an async function, you can use async/await to wait for the promise to resolve or reject.

import {connect, NatsConnectionOptions, Payload} from 'ts-nats';
// ...
try {
    let nc = await connect({servers: ['nats://', 'tls://']});
    // Do something with the connection
} catch(ex) {
    // handle the error
// ...

Since connect() returns a Promise, the promise patterns are supported. With no arguments, it will attempt to connect to nats://localhost:4222

    .then((nc) => {
        // Do something with the connection
    .catch((ex) => {
        // handle the error

Once you have a connection, you can publish data:

nc.publish('greeting', 'hello world!');

Subscribing allows you to receive messages published on a subject:

// simple subscription - subscribe returns a promise to a subscription object
let sub = await nc.subscribe('greeting', (err, msg) => {
    if(err) {
        // do something
    } else {
        // do something with

Subscription can respond to the publisher if the publisher sets a reply subject:

let service = await nc.subscribe('greeter', (err, msg) => {
    if(err) {
        // handle the error
    } else if (msg.reply) {
        nc.publish(msg.reply, `hello there ${}`);
// create an unique subject just to receive a response message
let inbox = nc.createInbox();
let sub2 = await nc.subscribe(inbox, (err, msg) => {
    if(err) {
        // handle the error
    } else {
}, {max: 1});
// publish a 'request' message
nc.publish('greeter', "NATS", inbox)
// stop getting messages on the service subscription
// didn't have to specify unsubscribe for sub2, the `{max: 1}` auto unsubscribes
// when the first message is received.

The above pattern is called Request/Reply - because it is so pervasive, ts-nats makes it very easy to make a request and handle a single response. The request API returns a Promise to a response message. All the bookkeeping, creating an inbox subject, creating a subscription to manage the response, and publishing details are handled. Since requests are expected to have a response, they require a timeout. If the request does not receive a response within the specified timeout, the promise rejects.

Subscriptions to handle request responses are very efficient since they utilize a shared subscription on the server. The client multiplexes the response without having to create and destroy subscriptions server-side.

let msg = await nc.request('greeter', 1000, 'me');

When done using a connection, closing it releases all resources, and cancels all subscriptions.


Wildcard Subscriptions

A single subscription can process related messages. When the subject specifies wildcards tokens, those parts of the subject can match different things. One of the wildcards is the * (asterisk). The asterisk in foo.*.baz matches all values in that token's position (, foo.a.baz, ...).

To work as a wildcard, the wildcard character must be the only character in the token. Asterisks that are part of a token value are interpreted as string literals, foo.a*.bar and will only match the literal value of foo.a*.bar.

let sub1 = await nc.subscribe('foo.*.baz', (err, msg) => {
    console.log('message received on', msg.subject, ":",;

Another wildcard is the > (greater than symbol). > tokens can only appear as the last token in a subject. foo.> will match,, When part of a token it is interpreted as a string literal> will only match>. Subscribing to > will match all subjects.

let sub2 = await nc.subscribe('foo.baz.>', (err, msg) => {
    console.log('message received on', msg.subject, ":",;

Queue Groups

All subscriptions with the same queue name will form a queue group. Each message will be delivered to only a single subscriber in the queue group. You can have as many queue groups as you wish. Normal subscribers and different queue groups are independent.

let sub3 = await nc.subscribe('foo.baz.>', (err, msg) => {
    console.log('message received on', msg.subject, ":",;
}, {queue: 'A'});

Clustered Usage

A NATS connection can specify several servers. When the NATS client connects to one of the servers, the server may gossip additional known cluster members. If the NATS client disconnects, it will attempt to connect to one of them.

let servers = ['nats://', 'nats://', 'nats://'];
// Randomly connect to a server in the cluster group.
let nc2 = await connect({servers: servers});

The client will randomize the list of servers that it manages to prevent a thundering herd of clients all at the same time trying to reconnect to the same server. To prevent randomization, specify the noRandomize option.

// Preserve order when connecting to servers.
let nc3 = await connect({servers: servers, noRandomize: true});


Using a TLS connection encrypts all traffic to the client. Secure connections are easy with NATS. Servers using TLS typically specify the tls protocol instead of nats. Strict tls requirements or options are specified by the tls option.

// Simple TLS connect
let ncs = await connect({url: 'tls://'});
// Client can explicitly request that the server be using tls
let ncs1 = await connect({url: 'tls://', tls: true});
// if CA is self signed:
import {readFileSync} from "fs";
let caCert = readFileSync('/path/to/cacert');
let ncs2 = await connect({url: 'tls://', tls: {
    ca: caCert
// client can verify server certificate:
let ncs3 = await connect({url: 'tls://', tls: {
    ca: caCert,
    rejectUnauthorized: true
// client can request to not validate server cert:
let ncs4 = await connect({url: 'tls://', tls: {
    rejectUnauthorized: false
// if server requires client certificates
import {readFileSync} from "fs";
let caCert = readFileSync('/path/to/cacert');
let clientCert = readFileSync('/path/to/clientCert');
let clientKey = readFileSync('/path/to/clientKey');
let ncs5 = await connect({url: 'tls://someserver:4443', tls: {
    ca: caCert,
    key: clientKey,
    cert: clientCert


User credentials can be specified in the URL or as NatsConnectionOptions:

// Connect with username and password in the url
let nc6 = await connect({url: 'nats://me:secret@'});
// Connect with username and password in the options
let nc7 = await connect({url: 'nats://', user: 'me', pass: 'secret'});
// Connect with token in url
let nc8 = await connect({url: 'nats://token@'});
// or token inside the options:
let nc9 = await connect({url: 'nats://', token: 'token'});

NKey Authentication

NKey authentication sends to the server a public nkey from the user, and signs a challenge. Server matches the public key with those allowed to connect and cryptographically verifies that the challenge was signed the user owning having the presented public key.

// Seed Keys should be treated as secrets
let nc11 = await connect({url: 'tls://', nkey: uPub, 
    nonceSigner: function(nonce:string): Buffer {
        // fromSeed is from ts-nkeys
        let sk = fromSeed(Buffer.from(uSeed));
        return sk.sign(Buffer.from(nonce));

JWT Authentication

JWT Authentication returns a JWT to the server and signs a challenge. The JWT includes the user's public key and permissions. The server resolves the issuer of the JWT (an account). If the server trusts account issuer, the user is authenticated. The server itself doesn't have a direct knowledge of the user or the account.

// Simples way to connect to a server using JWT and NKeys
let nc11 = await connect({url: 'tls://', userCreds: "/path/to/file.creds"});
// Setting nkeys and nonceSigner callbacks directly
// Seed Keys should be treated as secrets
// the nonceSigner function takes a seed key and returns the signed nonce
let nc12 = await connect({url: 'tls://',
    userJWT: uJWT, 
    nonceSigner: function(nonce:string): Buffer {
       // fromSeed is from ts-nkeys
       let sk = fromSeed(Buffer.from(uSeed));
       return sk.sign(Buffer.from(nonce));
// the user JWT can also be provided dynamically
let nc13 = await connect({url: 'tls://', 
    userJWT: function():string {
        return uJWT;
    nonceSigner: function(nonce:string): Buffer {
       // fromSeed is from ts-nkeys
       let sk = fromSeed(Buffer.from(uSeed));
       return sk.sign(Buffer.from(nonce));

Advanced Usage

NATS typically buffers messages sent to the server to reduce the number of kernel calls. This yields greater performance. The NATS client automatically buffers commands from the client and sends them. This buffering behaviour allows a NATS client to disconnect and continue to publish messages and create subscriptions briefly. On reconnect, the client sends all buffered messages and subscriptions to the server.

Sometimes a client wants to make sure that the NATS server has processed outgoing messages. The flush() will call a user-provided callback when the round trip to the server is done.

// Flush the connection and get notified when the server has finished processing
let ok = await nc.flush();
// or
nc.flush(() => {

A client can ensure that when the processing of incoming messages takes longer than some threshold, that time is given to other waiting IO tasks. In the example below, when processing takes longer than 10ms, the client will yield.

let nc10 = await connect({port: PORT, yieldTime: 10});

Subscriptions can auto cancel after it has received a specified number of messages:

nc.subscribe('foo', (err, msg) => {
    // do something
}, {max: 10});

Or if the expected message count is not received to timeout:

// Timeout if 10 messages are not received in specified time:
nc.subscribe('foo', (err, msg) => {
    // do something
}, {max: 10, timeout: 1000});

Timeouts and expected message counts can be specified via the subscription after it the subscription resolves:

let sub2 = await nc.subscribe('foo', (err, msg) => {
    // do something

Normally unsubscribe will cancel a subscription by sending a command to the server and then cancelling the message handler for the subscription. In such cases it is possible for messages waiting to be processed to be dropped.

To orderly unsubscribe, drain() sends the unsubscribe to the server and flushes with a handler that cancels the subscription. Because the cancel happens when the flush completes, drain ensures that the server will not send any additional messages to the subscription and that all sent messages have been processed by the client.

This functionality is particularly useful to queue subscribers.

let sub3 = await nc.subscribe('foo', (err, msg) => {
    // do something
// sometime in the future drain the subscription. Drain returns a promise
// when the drain promise resolves, the subscription finished processing 
// all pending inbound messages for the subscription.
let p = await sub3.drain();

Similarly to subscription drain(), an entire connection can be drained.

let nc10 = await connect();
// create subscriptions etc
// When drain is called:
// - no additional subscriptions or requests can be made.
// - all open subscriptions drain (including the global request/reply)
// When all drain requests resolve:
// - a flush is sent to the server to drain outbound messages
// - client closes
await nc10.drain();

Message payloads can be strings, binary, or JSON. Payloads determine the type of on subscriptions string, Buffer, or javascript object.

let nc12 = await connect({payload: Payload.STRING});
let nc13 = await connect({payload: Payload.JSON});
let nc14 = await connect({payload: Payload.BINARY});

String encodings can be set to node supported string encodings. The default encoding is utf-8, it only affects string payloads.

let nc14 = await connect({payload: Payload.STRING, encoding: "ascii"});

Connect and reconnect behaviours can be configured. You can specify the number of attempts and the interval between attempts on reconnects. By default a NATS connection will try to reconnect to a server ten times, waiting 2 seconds between reconnect attempts. If the maximum number of retries is reached, the client will close() the connection.

// Keep trying to reconnect forever, and attempt to reconnect every 250ms
let nc15 = await connect({maxReconnectAttempts: -1, reconnectTimeWait: 250});


The nats client is an EventEmitter, and thus emits various notifications:

Event Argument Description
close Emitted when the client closes. A closed client is finished, and cannot be reused.
connect Client, url (string), ServerInfo Emitted when the client first connects to a NATS server. Only happens once.
disconnect url Emitted when the client disconnects from a server.
error NatsError Emitted when the client receives an error. If an error handler is not set, the node process will exit.
permissionError NatsError Emitted when the server emits a permission error when subscribing or publishing to a subject that the client is not allowed to.
reconnect Client, url (string) Emitted when the server connects to a different server
reconnecting url (string) Emitted when the server attempts to reconnect to a different server
serversChanged ServersChangedEvent Emitted when the server gossips a list of other servers in the cluster. Only servers not specified in a connect list are deleted if they disapear.
subscribe SubEvent Emitted when a subscription is created on the client
unsubscribe SubEvent Emitted when a subscription is auto-unsubscribed
yield Emitted when the client's processing took longer than the specified yield option, and the client yielded.

See examples for more information.

Connect Options

The following is the list of connection options and default values.

Option Default Description
encoding "utf8" Encoding specified by the client to encode/decode data
maxPingOut 2 Max number of pings the client will allow unanswered before rasing a stale connection error
maxReconnectAttempts 10 Sets the maximun number of reconnect attempts. The value of -1 specifies no limit
name Optional client name (useful for debugging a client on the server output -DV)
nkey The public NKey identifying the client
noEcho false If set, the client's matching subscriptions won't receive messages published by the client. Requires server support 1.2.0+.
nonceSigner A NonceSigner function that signs the server challenge.
noRandomize false If set, the order of user-specified servers is randomized.
pass Sets the password for a connection
payload Payload.STRING Sets the payload type [Payload.STRING, Payload.BINARY, or Payload.JSON].
pedantic false Turns on strict subject format checks
pingInterval 120000 Number of milliseconds between client-sent pings
reconnect true If false server will not attempt reconnecting
reconnectTimeWait 2000 If disconnected, the client will wait the specified number of milliseconds between reconnect attempts
servers Array of connection urls
tls undefined This property can be a boolean or an Object. If true the client requires a TLS connection. If false a non-tls connection is required. undefined allows connecting to either secure or non-secured. The value can also be an object specifying TLS certificate data, which will implicitly require a secured connection. The properties ca, key, cert should contain the certificate file data. ca should be provided for self-signed certificates. key and cert are required for client provided certificates. rejectUnauthorized if true validates server's credentials
token Sets a authorization token for a connection
url "nats://localhost:4222" Connection url
user Sets the username for a connection
userCreds Path to a properly formatted user credentials file containing the client's JWT and seed key for the client. This property sets a nonceSigner automatically.
userJWT A string or a JWTProvider function which provides a JWT specifying the client's permissions
verbose false Turns on +OK protocol acknowledgements
waitOnFirstConnect false If true the server will fall back to a reconnect mode if it fails its first connection attempt.
yieldTime If set and processing exceeds yieldTime, client will yield to IO callbacks before processing additional inbound messages

Supported Node Versions

Support policy for Nodejs versions follows Nodejs release support. We will support and build ts-nats on even Nodejs versions that are current or in maintenance.


Unless otherwise noted, the NATS source files are distributed under the Apache Version 2.0 license found in the LICENSE file.


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