Connect FlowMQ with MQTT.js

FlowMQ's native support for MQTT makes it an excellent choice for JavaScript and Node.js applications. This guide will walk you through using MQTT.js, a popular and versatile MQTT client, to connect to FlowMQ, publish messages, and subscribe to topics.

Prerequisites

Before you start, ensure you have the following:

• A running instance of FlowMQ.
• Node.js v14 or later installed.
• npm or yarn for package management.

Installation

You can add MQTT.js to your project using your preferred package manager.

# Using npm
npm install mqtt

# Or using yarn
yarn add mqtt

Connecting to FlowMQ

To get started, you need to connect to your FlowMQ broker. The mqtt.connect() method returns a client instance.

const mqtt = require('mqtt');

const client = mqtt.connect('mqtt://localhost:1883', {
  clientId: 'my-js-client'
});

client.on('connect', () => {
  console.log('Connected to FlowMQ!');
  // ... proceed to subscribe or publish
});

Subscribing to Topics

Once connected, you can subscribe to one or more topics to start receiving messages.

client.on('connect', () => {
  console.log('Connected to FlowMQ!');
  
  client.subscribe('flowmq/test', (err) => {
    if (!err) {
      console.log('Subscribed to flowmq/test');
      // Now publish a message
      client.publish('flowmq/test', 'Hello FlowMQ from MQTT.js!');
    }
  });
});

Receiving Messages

You can listen for the message event on the client to process incoming messages from your subscriptions.

client.on('message', (topic, message) => {
  // message is a Buffer
  console.log(`Received message on topic ${topic}: ${message.toString()}`);
  
  // Close the connection after receiving the message
  client.end();
});

Full Example

Here is a complete Node.js script that connects, subscribes, publishes a message, and then handles the received message.

const mqtt = require('mqtt');

// Connect to the FlowMQ broker
const client = mqtt.connect('mqtt://localhost:1883', {
  clientId: 'my-javascript-client'
});

// Handle the connect event
client.on('connect', () => {
  console.log('Successfully connected to FlowMQ.');

  // Subscribe to a topic
  client.subscribe('flowmq/test/js', (err) => {
    if (!err) {
      console.log('Subscribed successfully!');
      
      // Publish a message to the same topic
      client.publish('flowmq/test/js', 'This is a test message from MQTT.js');
      console.log('Message published.');
    } else {
      console.error('Subscription failed:', err);
    }
  });
});

// Handle incoming messages
client.on('message', (topic, message) => {
  console.log(`Received message on topic '${topic}': ${message.toString()}`);
  
  // End the client connection gracefully
  client.end();
});

// Handle connection errors
client.on('error', (err) => {
  console.error('Connection error:', err);
  client.end();
});

Additional Resources

• For more advanced features, such as different QoS levels, retained messages, and browser usage, refer to the official MQTT.js repository.
• Explore FlowMQ's advanced features for MQTT.