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MQTT.js is a client library for the MQTT protocol, written in JavaScript for node.js and the browser.

MQTT.js is an OPEN Open Source Project, see the Contributing section to find out what this means.

Important notes for existing users

v1.0.0 improves the overall architecture of the project, which is now split into three components: MQTT.js keeps the Client, mqtt-connection includes the barebone Connection code for server-side usage, and mqtt-packet includes the protocol parser and generator. The new Client improves performance by a 30% factor, embeds Websocket support (MOWS is now deprecated), and it has a better support for QoS 1 and 2. The previous API is still supported but deprecated, as such, it id not documented in this README.

As a breaking change, the encoding option in the old client is removed, and now everything is UTF-8 with the exception of the password in the CONNECT message and payload in the PUBLISH message, which are Buffer.

Another breaking change is that MQTT.js now defaults to MQTT v3.1.1, so to support old brokers, please read the client options doc.


npm install mqtt --save


For the sake of simplicity, let's put the subscriber and the publisher in the same file:

var mqtt    = require('mqtt');
var client  = mqtt.connect('mqtt://');
client.on('connect', function () {
  client.publish('presence', 'Hello mqtt');
client.on('message', function (topic, message) {
  // message is Buffer


Hello mqtt

If you want to run your own MQTT broker, you can use Mosquitto or Mosca, and launch it. You can also use a test instance: and are both public.

If you do not want to install a separate broker, you can try using the server/orig example. It implements enough of the semantics of the MQTT protocol to run the example.

to use MQTT.js in the browser see the browserify section

Command Line Tools

MQTT.js bundles a command to interact with a broker. In order to have it available on your path, you should install MQTT.js globally:

npm install mqtt -g

Then, on one terminal

mqtt sub -t 'hello' -h '' -v

On another

mqtt pub -t 'hello' -h '' -m 'from MQTT.js'

See mqtt help <command> for the command help.


mqtt.connect([url], options)

Connects to the broker specified by the given url and options and returns a Client.

The URL can be on the following protocols: 'mqtt', 'mqtts', 'tcp', 'tls', 'ws', 'wss'. The URL can also be an object as returned by URL.parse(), in that case the two objects are merged, i.e. you can pass a single object with both the URL and the connect options.

You can also specify a servers options with content: [{ host: 'localhost', port: 1883 }, ... ], in that case that array is iterated at every connect.

For all MQTT-related options, see the Client constructor.

mqtt.Client(streamBuilder, options)

The Client class wraps a client connection to an MQTT broker over an arbitrary transport method (TCP, TLS, WebSocket, ecc).

Client automatically handles the following:

  • Regular server pings
  • QoS flow
  • Automatic reconnections
  • Start publishing before being connected

The arguments are:

  • streamBuilder is a function that returns a subclass of the Stream class that supports the connect event. Typically a net.Socket.
  • options is the client connection options (see: the connect packet). Defaults:
    • keepalive: 10 seconds, set to 0 to disable
    • clientId: 'mqttjs'_ + crypto.randomBytes(16).toString('hex')
    • protocolId: 'MQTT'
    • protocolVersion: 4
    • clean: true, set to false to receive QoS 1 and 2 messages while offline
    • reconnectPeriod: 1000 milliseconds, interval between two reconnections
    • connectTimeout: 30 * 1000 milliseconds, time to wait before a CONNACK is received
    • username: the username required by your broker, if any
    • password: the password required by your broker, if any
    • incomingStore: a Store for the incoming packets
    • outgoingStore: a Store for the outgoing packets
    • will: a message that will sent by the broker automatically when the client disconnect badly. The format is:
      • topic: the topic to publish
      • payload: the message to publish
      • qos: the QoS
      • retain: the retain flag

In case mqtts (mqtt over tls) is required, the options object is passed through to tls.connect(). If you are using a self-signed certificate, pass the rejectUnauthorized: false option. Beware that you are exposing yourself to man in the middle attacks, so it is a configuration that is not recommended for production environments.

If you are connecting to a broker that supports only MQTT 3.1 (not 3.1.1 compliant), you should pass these additional options:

  protocolId: 'MQIsdp',
  protocolVersion: 3

This is confirmed on RabbitMQ 3.2.4, and on Mosquitto < 1.3. Mosquitto version 1.3 and 1.4 works fine without those.

Event 'connect'

function() {}

Emitted on successful (re)connection (i.e. connack rc=0).

Event 'reconnect'

function() {}

Emitted when a reconnect starts.

Event 'close'

function() {}

Emitted after a disconnection.

Event 'offline'

function() {}

Emitted when the client goes offline.

Event 'error'

function(error) {}

Emitted when the client cannot connect (i.e. connack rc != 0) or when a parsing error occurs.

Event 'message'

function(topic, message, packet) {}

Emitted when the client receives a publish packet

  • topic topic of the received packet
  • message payload of the received packet
  • packet received packet, as defined in mqtt-packet

mqtt.Client#publish(topic, message, [options], [callback])

Publish a message to a topic

  • topic is the topic to publish to, String
  • message is the message to publish, Buffer or String
  • options is the options to publish with, including:
    • qos QoS level, Number, default 0
    • retain retain flag, Boolean, default false
  • callback callback fired when the QoS handling completes, or at the next tick if QoS 0.

mqtt.Client#subscribe(topic/topic array/topic object, [options], [callback])

Subscribe to a topic or topics

  • topic is a String topic to subscribe to or an Array of topics to subscribe to. It can also be an object, it has as object keys the topic name and as value the QoS, like {'test1': 0, 'test2': 1}.
  • options is the options to subscribe with, including:
    • qos qos subscription level, default 0
  • callback - function(err, granted) callback fired on suback where:
    • err a subscription error
    • granted is an array of {topic, qos} where:
      • topic is a subscribed to topic
      • qos is the granted qos level on it

mqtt.Client#unsubscribe(topic/topic array, [options], [callback])

Unsubscribe from a topic or topics

  • topic is a String topic or an array of topics to unsubscribe from
  • callback fired on unsuback

mqtt.Client#end([force], [cb])

Close the client, accepts the following options:

  • force: passing it to true will close the client right away, without waiting for the in-flight messages to be acked. This parameter is optional.
  • cb: will be called when the client is closed. This parameter is optional.

mqtt.Client#handleMessage(packet, callback)

Handle messages with backpressure support, one at a time. Override at will, but always call callback, or the client will hang.


In-memory implementation of the message store.

Another implementaion is mqtt-level-store which uses Level-browserify to store the inflight data, making it usable both in Node and the Browser.

mqtt.Store#put(packet, callback)

Adds a packet to the store, a packet is anything that has a messageId property. The callback is called when the packet has been stored.


Creates a stream with all the packets in the store.

mqtt.Store#del(packet, cb)

Removes a packet from the store, a packet is anything that has a messageId property. The callback is called when the packet has been removed.


Closes the Store.


In order to use MQTT.js as a browserify module you can either require it in your browserify bundles or build it as a stand alone module. The exported module is AMD/CommonJs compatible and it will add an object in the global space.

npm install -g browserify // install browserify
cd node_modules/mqtt
npm install . // install dev dependencies
browserify mqtt.js -s mqtt > browserMqtt.js // require mqtt in your client-side app

you can then use mqtt.js in the browser with the same api than node's one.

  <title>test Ws mqtt.js</title>
<script src="./browserMqtt.js"></script>
      var client = mqtt.connect(); // you add a ws:// url here
      client.on("message", function(topic, payload) {
        alert([topic, payload].join(""));
      client.publish("mqtt/demo", "hello world!");

Your broker should accept websocket connection (see MQTT over Websockets to setup Mosca).


MQTT.js is an OPEN Open Source Project. This means that:

Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the file for more details.


MQTT.js is only possible due to the excellent work of the following contributors:

Adam RuddGitHub/adamvrTwitter/@adam_vr
Matteo CollinaGitHub/mcollinaTwitter/@matteocollina



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