React (also known as React.js or ReactJS) is an open-source, front end, JavaScript library for building user interfaces or UI components. It is maintained by Facebook and a community of individual developers and companies. React can be used as a base in the development of single-page or mobile applications. However, React is only concerned with rendering data to the DOM, and so creating React applications usually requires the use of additional libraries for state management and routing. Redux and React Router are respective examples of such libraries.¹

This article mainly introduces how to use MQTT in the React project for implementing connect, subscribe, messaging and unsubscribe, etc., between the client and MQTT broker.

Project Initialisation

New Project

Reference link: https://reactjs.org/docs/getting-started.html

Creating new React applications with Create React App

  npx create-react-app react-mqtt-test

If you need to use TypeScript, simply add the --template typescript parameter at the end of the command line

  npx create-react-app react-mqtt-test --template typescript

Then add the TypeScript type library required in the React project

  npm install --save typescript @types/node @types/react @types/react-dom @types/jest
  # or
  yarn add typescript @types/node @types/react @types/react-dom @types/jest

The use of TypeScript will not be the focus of the examples in this article, but if you wish to use it, you can add TypeScript features after referring to the creation example and the full code examples.

Import via CDN

  <script crossorigin src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
  <script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>

Install the MQTT Client Library

As React is a JavaScript library, it is possible to use MQTT.js as the MQTT client library.

The following methods 2, 3 are more suitable for referencing projects created by React via CDN links.

Installation via the command line, either using the npm or yarn command (one or the other)

   npm install mqtt --save
   # or
   yarn add mqtt

Import via CDN

   <script src="https://unpkg.com/mqtt/dist/mqtt.min.js"></script>

Download to the local and then import using the relative path

   <script src="/your/path/to/mqtt.min.js"></script>

The Use of MQTT

Connect the MQTT Broker

This article will use the free public MQTT broker which is provided by EMQX. This service is based on EMQX's MQTT IoT cloud platform to create. The server access information is as follows.

Broker: broker.emqx.io
TCP Port: 1883
Websocket Port: 8083

Connect

const [client, setClient] = useState(null);
const mqttConnect = (host, mqttOption) => {
  setConnectStatus('Connecting');
  setClient(mqtt.connect(host, mqttOption));
};
useEffect(() => {
  if (client) {
    console.log(client)
    client.on('connect', () => {
      setConnectStatus('Connected');
    });
    client.on('error', (err) => {
      console.error('Connection error: ', err);
      client.end();
    });
    client.on('reconnect', () => {
      setConnectStatus('Reconnecting');
    });
    client.on('message', (topic, message) => {
      const payload = { topic, message: message.toString() };
      setPayload(payload);
    });
  }
}, [client]);

const mqttSub = (subscription) => {
  if (client) {
    const { topic, qos } = subscription;
    client.subscribe(topic, { qos }, (error) => {
      if (error) {
        console.log('Subscribe to topics error', error)
        return
      }
      setIsSub(true)
    });
  }
};

Unsubscribe

const mqttUnSub = (subscription) => {
  if (client) {
    const { topic } = subscription;
    client.unsubscribe(topic, error => {
      if (error) {
        console.log('Unsubscribe error', error)
        return
      }
      setIsSub(false);
    });
  }
};

Publish

const mqttPublish = (context) => {
  if (client) {
    const { topic, qos, payload } = context;
    client.publish(topic, payload, { qos }, error => {
      if (error) {
        console.log('Publish error: ', error);
      }
    });
  }
}

Disconnect

const mqttDisconnect = () => {
  if (client) {
    client.end(() => {
      setConnectStatus('Connect');
    });
  }
}

Test

We have written the following simple browser application using React with the ability to create connections, subscribe to topics, send and receive messages, unsubscribe, and disconnect.

The complete project example code: https://github.com/emqx/MQTT-Client-Examples/tree/master/mqtt-client-React。

Use MQTT 5.0 client tool - MQTT X as another client to test sending and receiving messages.

You can see that MQTT X can receive messages from the browser side normally, as can be seen when sending a message to the topic using MQTT X.

Summary

In summary, we have implemented the creation of an MQTT connection in the React project, and simulated subscribing, sending and receiving messages, unsubscribing and disconnecting between the client and MQTT broker.

In this article, we use React v16.13.1, so the Hook Component feature will be used as example code to demonstrate, or if required, you can refer to the ClassMqtt component in the full example code to use the Class Component feature for project building.

https://en.wikipedia.org/wiki/React_(web_framework) ↩

How to Use MQTT in the React Project