在文件之间共享mqtt客户端对象 [英] share mqtt client object between files
问题描述
我通过以下方式连接到MQTT:
I connect to MQTT this way:
//mqtt.js
const mqtt = require('mqtt');
var options = {
//needed options
};
var client = mqtt.connect('mqtt://someURL', options);
client.on('connect', () => {
console.log('Connected to MQTT server');
});
我想以这种方式导出 client 对象:
I want to export the client object this way:
//mqtt.js
module.exports = client;
这样我就可以将其导入其他文件并以这种方式使用它:
So that I can import it in other files and make use of it this way:
//anotherFile.js
const client = require('./mqtt');
client.publish(...)
但是,我们都知道这将行不通!我该如何实现?
However, we all know that this will not work! How can I achieve this ?
更新
我尝试了 promise (诺言),并且得到了一个非常奇怪的行为.当我在以下文件的同一文件(mqtt.js)中使用promise时,一切正常:
I tried promise and get a very strange behavior. When I use the promise in the same file (mqtt.js) like the code below, everything is OK:
//mqtt.js
const mqtt = require('mqtt');
var mqttPromise = new Promise(function (resolve, reject) {
var options = {
//needed options
};
var client = mqtt.connect('mqtt://someURL', options);
client.on('connect', () => {
client.subscribe('#', (err) => {
if (!err) {
console.log('Connected to MQTT server');
resolve(client);
} else {
console.log('Error: ' + err);
reject(err);
}
});
});
});
mqttPromise.then(function (client) {
//do sth with client
}, function (err) {
console.log('Error: ' + err);
});
但是当我导出promise并在另一个文件中使用它时,就像这样:
But when I export the promise and use it in another file, like this:
//mqtt.js
//same code to create the promise
module.exports = mqttPromise;
//anotherFile.js
const mqttPromise = require('./mqtt');
mqttPromise.then(function (client) {
//do sth with client
}, function (err) {
console.log('Error: ' + err);
});
我收到此错误:
TypeError:mqttPromise.那不是函数
TypeError: mqttPromise.then is not a function
推荐答案
您可能可以实现创建2个文件的目标,一个文件用于处理mqtt方法,另一个文件用于管理连接对象.
You can probably achieve your goal creating 2 files, one for handling mqtt methods and another to manage the connection object.
这是mqtt处理程序的文件:
Here's the file for the mqtt handler:
//mqttHandler.js
const mqtt = require('mqtt');
class MqttHandler {
constructor() {
this.mqttClient = null;
this.host = 'YOUR_HOST';
this.username = 'YOUR_USER';
this.password = 'YOUR_PASSWORD';
}
connect() {
this.mqttClient = mqtt.connect(this.host, {port: 1883});
// Mqtt error calback
this.mqttClient.on('error', (err) => {
console.log(err);
this.mqttClient.end();
});
// Connection callback
this.mqttClient.on('connect', () => {
console.log(`mqtt client connected`);
});
this.mqttClient.on('close', () => {
console.log(`mqtt client disconnected`);
});
}
// // Sends a mqtt message to topic: mytopic
sendMessage(message, topic) {
this.mqttClient.publish(topic, JSON.stringify(message));
}
}
module.exports = MqttHandler;
现在,让我们使用导出的模块在另一个文件上创建mqtt客户端连接:
Now lets use the exported module to create a mqtt client connection on another file:
//mqttClient.js
var mqttHandler = require('./mqttHandler');
var mqttClient = new mqttHandler();
mqttClient.connect();
module.exports = mqttClient;
使用此导出的模块,您现在可以调用客户端连接对象,并使用在另一个文件中的mqttHandler.js文件中创建的方法:
With this exported module you can now call your client connection object and use the methods created in the mqttHandler.js file in another file :
//main.js
var mqttClient = require('./mqttClient');
mqttClient.sendMessage('<your_topic>','<message>');
尽管可能有更好的方法来执行任务,但是这个方法对我来说效果很好...
Although there may be a better method to perform your task, this one worked pretty well for me...
希望有帮助!
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