• MQTT ---> Message Queuing Telemetry Transport

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

• MQTT is a lightweight client-server publish/subscribe messaging protocol

• MQTT is used for data exchange between devices and server applications

installation

npm install mqtt --save

component

1. Publisher
2. broker --- inside broker there are some queues
3. subscriber

methods

1. connect

client.on('connect', function (connack) {
   console.log('Connected')
})

2. reconnect

client.on('reconnect', function () {
  console.log('Reconnecting...')
})

3. close

client.on('close', function () {
  console.log('Disconnected')
})

4. disconnect

client.on('disconnect', function (packet) {
   console.log(packet)
})

5. publish

Client.publish(topic, message, [options], [callback]
                🔽
client.publish('topic', 'Hello world')
                🔽
client.publish('testtopic', 'Hello, function () {
    console.log('Published')
})

6. subscribe

client.subscribe('test', function (err) {
    console.log(error)
})

7. error

client.on('error', function (error) {
  console.log(error)
})

8. message

client.on('message', function (topic, payload, packet) {
  console.log(`Topic: ${topic}, Message: ${payload.toString()}, QoS: ${packet.qos}`)
})