Paho Javascript MQTT订阅多个主题

Question

当客户端订阅多个主题时，是否可以使用与paho python中使用的message_callback_add类似的概念(在javascript中(来使用多个回调？我在onMessageArrived()中看到了if条件的使用，但我想知道是否存在更高效、更干净的方法？

var mqtt;                           // MQTT variable/object
var reconnectTimeout = 5000;        // 5 seconds for the reconnectTimeout
var host="localhost";               // MQTT bridge IP
var port=8083;                      // MQTT bridge port 
MQTTconnect();                      // Initialise the MQTT connections
function MQTTconnect(){
console.log("mqtt connecting to " + host + ":" + port);
mqtt = new Paho.MQTT.Client(host, port, "client_test");
var options = {
timeout: 100,
onSuccess: onConnect,
onFailure: onFailure,
};
mqtt.onMessageArrived = onMessageArrived;
mqtt.connect(options); // connect
}
function onConnect(){
console.log("Mqtt Connected - Subscribe to the topics");
mqtt.subscribe("topic1/a");
mqtt.subscribe("topic2/b");
}

function onFailure(message){
console.log("Connection attempt to MQTT " + host + " failed");
setTimeout(MQTTconnect, reconnectTimeout);
}
function onMessageArrived(msg){
if (msg.destinationName == "topic1/a"){
console.log("Topic1: ", msg.payloadString);
}
else if (msg.destinationName == "topic2/b"){
console.log("Topic2: ", msg.payloadString);
}
}

Answer 1

不，JavaScript中的所有消息只有一个回调。

唯一的选项是根据需要在onMessageArrived回调中检查主题和分支

Answer 2

库可能没有它，但可以创建自己的回调逻辑！这里有一个漂亮的解决方案：

import EventEmitter from 'events';
const emitter = new EventEmitter();
client.subscribe('my_topic_1');
client.subscribe('my_topic_2');
client.onMessageArrived = onMessage;
function onMessageArrived(message) {
emitter.emit(message.topic, message.payloadString);
}
function subscribe(event, callback) {
emitter.addListener(event, callback);
}
function unsubscribe(event, callback) {
emitter.removeListener(event, callback);
}
subscribe('my_topic_1', (string) => {
console.log('only my_topic_1 messages', string);
});