What is mqtt?
The mqtt npm package is a client library for the MQTT protocol, which is a lightweight messaging protocol designed for small sensors and mobile devices. It allows you to connect to an MQTT broker, publish messages to topics, and subscribe to topics to receive messages.
What are mqtt's main functionalities?
Connect to an MQTT broker
This feature allows you to connect to an MQTT broker. The code sample demonstrates how to connect to a public MQTT broker (HiveMQ) and log a message upon successful connection.
const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
console.log('Connected to broker');
});
Publish messages to a topic
This feature allows you to publish messages to a specific topic. The code sample shows how to publish a message 'Hello MQTT' to the topic 'test/topic' after connecting to the broker.
const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
client.publish('test/topic', 'Hello MQTT');
console.log('Message published');
});
Subscribe to a topic
This feature allows you to subscribe to a specific topic and receive messages published to that topic. The code sample demonstrates subscribing to 'test/topic' and logging any received messages.
const mqtt = require('mqtt');
const client = mqtt.connect('mqtt://broker.hivemq.com');
client.on('connect', () => {
client.subscribe('test/topic', (err) => {
if (!err) {
console.log('Subscribed to topic');
}
});
});
client.on('message', (topic, message) => {
console.log(`Received message: ${message.toString()} on topic: ${topic}`);
});
Other packages similar to mqtt
mqttjs
mqttjs is another popular MQTT client library for Node.js. It offers similar functionalities to the mqtt package, including connecting to brokers, publishing, and subscribing to topics. It is known for its simplicity and ease of use.
aedes
aedes is a barebone MQTT broker that can be embedded in Node.js applications. While it serves as a broker rather than a client, it can be used in conjunction with mqtt to create a complete MQTT solution. It is lightweight and highly performant.
mosca
mosca is an MQTT broker that can be used with Node.js. It is designed to be fast and scalable, making it suitable for IoT applications. Like aedes, it can be used alongside mqtt to provide a full MQTT ecosystem.
mqtt.js 
Introduction
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mqtt.js is a library for the MQTT protocol, written
in JavaScript to be used in node.js.
Important notes for existing users
-
v0.3.0 improves connection stability, performance, the reconnection
logic and SSL support. See #118 for
details. A Connection is a Writable stream, so you can run
MQTT.js over any kind of Stream (doc needed). Both the constructors of
MqttClient and MqttConnection changed, but not the factory method
mqtt.createClient
and mqtt.createConnection
.
-
v0.2.0 has brough some API breaking changes to mqtt.js.
Please consult the migration guide for information
or open an issue if you need any help.
Installation
npm install mqtt
Example
First you will need to install and run a broker, such as
Mosquitto or
Mosca, and launch it.
For the sake of simplicity, let's put the subscriber and the publisher in the same file:
var mqtt = require('mqtt')
client = mqtt.createClient(1883, 'localhost');
client.subscribe('presence');
client.publish('presence', 'Hello mqtt');
client.on('message', function (topic, message) {
console.log(message);
});
client.end();
output:
Hello mqtt
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.
Documentation
Detailed documentation can be found in the wiki
Client API usage
See: examples/client
Simple publish client
var mqtt = require('mqtt')
, client = mqtt.createClient();
client.publish('messages', 'mqtt');
client.publish('messages', 'is pretty cool');
client.publish('messages', 'remember that!', {retain: true});
client.end();
Simple subscribe client
var mqtt = require('mqtt')
, client = mqtt.createClient();
client.subscribe('messages');
client.publish('messages', 'hello me!');
client.on('message', function(topic, message) {
console.log(message);
});
client.options.reconnectPeriod = 0;
Chainable API!
var mqtt = require('mqtt')
, client = mqtt.createClient();
client
.subscribe('messages')
.publish('presence', 'bin hier')
.on('message', function(topic, message) {
console.log(topic);
});
Server API usage
Broadcast server example
Included in examples/broadcast.js:
var mqtt = require('mqtt');
mqtt.createServer(function(client) {
var self = this;
if (!self.clients) self.clients = {};
client.on('connect', function(packet) {
client.connack({returnCode: 0});
client.id = packet.clientId;
self.clients[client.id] = client;
});
client.on('publish', function(packet) {
for (var k in self.clients) {
self.clients[k].publish({topic: packet.topic, payload: packet.payload});
}
});
client.on('subscribe', function(packet) {
var granted = [];
for (var i = 0; i < packet.subscriptions.length; i++) {
granted.push(packet.subscriptions[i].qos);
}
client.suback({granted: granted, messageId: packet.messageId});
});
client.on('pingreq', function(packet) {
client.pingresp();
});
client.on('disconnect', function(packet) {
client.stream.end();
});
client.on('close', function(err) {
delete self.clients[client.id];
});
client.on('error', function(err) {
client.stream.end();
console.log('error!');
});
}).listen(1883);
License
MIT