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1.2.10 • Public • Published

NATS - Node.js Client

A Node.js client for the NATS messaging system.

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npm install nats

Basic Usage

var NATS = require('nats');
var nats = NATS.connect();
// Simple Publisher
nats.publish('foo', 'Hello World!');
// Simple Subscriber
nats.subscribe('foo', function(msg) {
  console.log('Received a message: ' + msg);
// Unsubscribing
var sid = nats.subscribe('foo', function(msg) {});
// Request Streams
var sid = nats.request('request', function(response) {
  console.log('Got a response in msg stream: ' + response);
// Request with Auto-Unsubscribe. Will unsubscribe after
// the first response is received via {'max':1}
nats.request('help', null, {'max':1}, function(response) {
  console.log('Got a response for help: ' + response);
// Request for single response with timeout.
nats.requestOne('help', null, {}, 1000, function(response) {
  // `NATS` is the library.
  if(response instanceof NATS.NatsError && response.code === NATS.REQ_TIMEOUT) {
    console.log('Request for help timed out.');
  console.log('Got a response for help: ' + response);
// Replies
nats.subscribe('help', function(request, replyTo) {
  nats.publish(replyTo, 'I can help!');
// Close connection


The json connect property makes it easier to exchange JSON data with other clients.

var nc = NATS.connect({json: true});
nc.on('connect', function() {
    nc.on('error', function(err) {
    nc.subscribe("greeting", function(msg, reply) {
        // msg is a parsed JSON object object
        if( && msg.reply) {
            nc.publish(reply, {greeting: "hello " +});
    // As with all inputs from unknown sources, if you don't trust the data
    // you should verify it prior to accessing it. While JSON is safe because
    // it doesn't export functions, it is still possible for a client to
    // cause issues to a downstream consumer that is not written carefully
    nc.subscribe("unsafe", function(msg) {
        // for example a client could inject a bogus `toString` property
        // which could cause your client to crash should you try to
        // concatenation with the `+` like this:
        // console.log("received", msg + "here");
        // `TypeError: Cannot convert object to primitive value`
        // Note that simple `console.log(msg)` is fine.
        if (msg.hasOwnProperty('toString')) {
            console.log('tricky - trying to crash me:', msg.toString);
        // of course this is no different than using a value that is
        // expected in one format (say a number), but the client provides
        // a string:
        if (isNaN(msg.amount) === false) {
            // do something with the number
    // the bad guy
    nc.publish("unsafe", {toString: "no good"});
    nc.flush(function() {

Wildcard Subscriptions

// "*" matches any token, at any level of the subject.
nats.subscribe('foo.*.baz', function(msg, reply, subject) {
  console.log('Msg received on [' + subject + '] : ' + msg);
nats.subscribe('*', function(msg, reply, subject) {
  console.log('Msg received on [' + subject + '] : ' + msg);
// ">" matches any length of the tail of a subject, and can only be
// the last token E.g. 'foo.>' will match '', '',
// ''
nats.subscribe('foo.>', function(msg, reply, subject) {
  console.log('Msg received on [' + subject + '] : ' + msg);

Queue Groups

// All subscriptions with the same queue name will form a queue group.
// Each message will be delivered to only one subscriber per queue group,
// queuing semantics. You can have as many queue groups as you wish.
// Normal subscribers will continue to work as expected.
nats.subscribe('foo', {'queue':'job.workers'}, function() {
  received += 1;

Clustered Usage

var nats = require('nats');
var servers = ['nats://', 'nats://', 'nats://'];
// Randomly connect to a server in the cluster group.
var nc = nats.connect({'servers': servers});
// currentServer is the URL of the connected server.
console.log("Connected to " +;
// Preserve order when connecting to servers.
nc = nats.connect({'dontRandomize': true, 'servers':servers});


var nats = require('nats');
var fs = require('fs');
// Simple TLS connect
var nc = nats.connect({port: TLSPORT, tls: true});
// Overriding and not verifying the server
var tlsOptions = {
  rejectUnauthorized: false,
var nc = nats.connect({port: TLSPORT, tls: tlsOptions});
// will be false
// Use a specified CA for self-signed server certificates
var tlsOptions = {
  ca: [ fs.readFileSync('./test/certs/ca.pem') ]
var nc = nats.connect({port: TLSPORT, tls: tlsOptions});
// should be true
// Use a client certificate if the server requires
var tlsOptions = {
  key: fs.readFileSync('./test/certs/client-key.pem'),
  cert: fs.readFileSync('./test/certs/client-cert.pem'),
  ca: [ fs.readFileSync('./test/certs/ca.pem') ]
var nc = nats.connect({port: TLSPORT, tls: tlsOptions});

New Authentication (Nkeys and User Credentials)

See examples for more usage.

// Simple connect using credentials file. This loads JWT and signing key
// each time that NATS connects.
var nc = NATS.connect('', NATS.creds("./myid.creds"));
// Setting nkey and signing callback directly.
var nc = NATS.connect(url, {
    sigCB: function(nonce) {
      return sk.sign(nonce);
// Setting user JWT statically.
var nc = NATS.connect(url, {
    userJWT: myJWT,
    sigCB: function(nonce) {
      return sk.sign(nonce);
// Having user JWT be a function that returns the JWT. Can be useful for
// loading a new JWT.
var nc = NATS.connect(url, {
    userJWT: function() {
      return myJWT;
    sigCB: function(nonce) {
      return sk.sign(nonce);

Basic Authentication

// Connect with username and password in the url
var nc = NATS.connect("nats://foo:bar@localhost:4222");
// Connect with username and password inside object
var nc = NATS.connect({'url':"nats://localhost:4222", 'user':'foo', 'pass':'bar'});
// Connect with token in url
var nc = NATS.connect("nats://mytoken@localhost:4222");
// Connect with token inside object
var nc = NATS.connect({'url':"nats://localhost:4222", 'token':'mytoken'});

Advanced Usage

// Publish with closure, callback fires when server has processed the message
nats.publish('foo', 'You done?', function() {
  console.log('msg processed!');
// Flush connection to server, callback fires when all messages have
// been processed.
nats.flush(function() {
  console.log('All clear!');
// If you want to make sure NATS yields during the processing
// of messages, you can use an option to specify a yieldTime in ms.
// During the processing of the inbound stream, we will yield if we
// spend more then yieldTime milliseconds processing.
var nc = nats.connect({port: PORT, yieldTime: 10});
// Timeouts for subscriptions
var sid = nats.subscribe('foo', function() {
  received += 1;
// Timeout unless a certain number of messages have been received
nats.timeout(sid, timeout_ms, expected, function() {
  timeout = true;
// Auto-unsubscribe after MAX_WANTED messages received
nats.subscribe('foo', {'max':MAX_WANTED});
nats.unsubscribe(sid, MAX_WANTED);
// Multiple connections
var nats = require('nats');
var nc1 = nats.connect();
var nc2 = nats.connect();
// Encodings
// By default messages received will be decoded using UTF8. To change that,
// set the encoding option on the connection.
nc = nats.connect({'servers':servers, 'encoding': 'ascii'});
// PreserveBuffers
// To prevent payload conversion from a Buffer to a string, set the
// preserveBuffers option to true. Message payload return will be a Buffer.
nc = nats.connect({'preserveBuffers': true});
// Reconnect Attempts and Time between reconnects
// By default a NATS connection will try to reconnect to a server 10 times
// waiting 2 seconds between reconnect attempts. If the maximum number of
// retries is reached, the client will close the connection.
// To change the default behaviour specify the max number of connection
// attempts in `maxReconnectAttempts` (set to -1 to retry forever), and the
// time in milliseconds between reconnects in `reconnectTimeWait`.
nc = nats.connect({'maxReconnectAttempts': -1, 'reconnectTimeWait': 250});
nc.on('error', function(err) {
nc.on('connect', function(nc) {
nc.on('disconnect', function() {
nc.on('reconnecting', function() {
nc.on('reconnect', function(nc) {
nc.on('close', function() {

See examples and benchmarks for more information.

Connect Options

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

Option Aliases Default Description
noEcho false Subscriptions receive messages published by the client. Requires server support (1.2.0). If set to true, and the server does not support the feature, an error with code NO_ECHO_NOT_SUPPORTED is emitted, and the connection is aborted. Note that it is possible for this error to be emitted on reconnect when the server reconnects to a server that does not support the feature.
encoding "utf8" Encoding specified by the client to encode/decode data
json false If true, message payloads are converted to/from JSON
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 client Optional client name
noRandomize dontRandomize, NoRandomize false If set, the order of user-specified servers is randomized.
pass password Sets the password for a connection
pedantic false Turns on strict subject format checks
pingInterval 120000 Number of milliseconds between client-sent pings
preserveBuffers false If true, data for a message is returned as Buffer
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 urls Array of connection urls
tls secure false 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. The value can also be an object specifying TLS certificate data. 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 uri "nats://localhost:4222" Connection url
useOldRequestStyle false If set to true calls to request() and requestOne() will create an inbox subscription per call.
user Sets the username for a connection
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, processing will yield at least the specified number of milliseconds to IO callbacks before processing inbound messages

Supported Node Versions

Our support policy for Nodejs versions follows Nodejs release support. We will support and build node-nats on even-numbered Nodejs versions that are current or in LTS.


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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