MQTT. JS introductory tutorial: learning notes

MQTT.js Introductory tutorial

One 、 create a file ：【mqtt.js client 】

1、 New folder mqtt_pure, establish mqtt.js file ;
2、 stay VSCode Open in , Open a new one terminal ;
3、 Input... In the terminal npm install mqtt --save
4、 Write code ：

const mqtt = require('mqtt')
const options = {
    
    // Clean session
    clean: true,
    connectTimeout: 4000,
    // Auth
    clientId: 'emqx_test_lzl_mqttjs',
    username: 'emqx_test',
    password: 'emqx_test',
}

//  Make sure TCP Port  The port is correct 
const client = mqtt.connect('mqtt://broker.emqx.io:1883', options)

client.on('connect', function () {
    
    console.log('Connected')
    //  After subscribing to the topic , Trigger only once .
    client.subscribe('testtopic/lzl-MQTTX', function (err) {
    
        if (!err) {
    
            console.log("subscribe success!!!!")
            // Release theme testtopic/lzl-mqttjs
            client.publish('testtopic/lzl-mqttjs', 'Hello,  I am a mqttjs Client message . Through the theme 【testtopic/lzl-mqttjs】 Released from . from: client.subscribe')
        }
    })
}),

//  As long as the client message is received , It will trigger .
client.on('message', function (topic, message) {
    
    console.log(message.toString())

    client.publish('testtopic/lzl-mqttjs', 'Hello,  I am a mqttjs Client message .  Through the theme 【testtopic/lzl-mqttjs】 Released from .from: client.on')
}),

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

• Code directory ：
  
  5、 The input terminal node mqtt.js Run code .

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Two 、 note ：

2.1、【mqtt.js client 】 And 【MQTTX client 】

（1） Two clients （mqtt.js MQTTX） Connect to the same server .

（2）clientID： Globally unique . If different devices use the same clientID At the same time, connect to the Internet of things platform , Then the device connected first will be forcibly disconnected .

（3）【MQTTX client 】 Of clientID, and 【mqtt.js client 】 Of clientID Cannot be the same , The client connected to the server clientID Must be unique , Otherwise, it will crowd out other clients .

• I set up 【MQTTX client 】 Of clientID：emqx_test_lzl_MQTTX.
  Be careful ： You have to use the Internet to access the server , There will be a wall partition in the company's intranet .
• I set up 【mqtt.js client 】 Of clientId: 'emqx_test_lzl_mqttjs'

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2.2、 News subscription

1、 function node mqtt.js, stay 【mqttx.js client 】 subscribe 【MQTTX client 】 The news of ：

2、 Command line subscription messages

mqtt sub -t 'testtopic/#' -h 'broker.emqx.io' -v  //  Connect to  broker.emqx.io  And subscribe to  testtopic/#  The theme ;
 notes ：
1、testtopic/#             representative 【mqtt.js client 】 Subscribe to all testtopic/ Content under the topic .
2、testtopic/lzl-MQTTX     representative 【mqtt.js client 】 Only accept mine 【MQTTX client 】 Published topic content .