Connect after constructing client

[nandlab]

Is there a way to first construct the client object with certain options and later connect to the broker?
In some use cases it would be more convenient.

[rrebase]

I'd also find it useful to have a simple way of constructing the client object. Use case: add events listeners to f.e. packetsend, packetreceive before actually connecting to the broker.

[Vincent-SV]

I was looking exactly for this, because in the python package you create the client, then declare the callbacks, then use a .connect() method.
In the official documentation for this node mqtt package, this code is provided :

const mqtt = require('mqtt')
const client  = mqtt.connect('mqtt://test.mosquitto.org')

client.on('connect', function () {
  client.subscribe('presence', function (err) {
    if (!err) {
      client.publish('presence', 'Hello mqtt')
    }
  })
})

client.on('message', function (topic, message) {
  // message is Buffer
  console.log(message.toString())
  client.end()
})

And the "on connect" callback is declared after the connection, which bothers me a lot.
From what I understand, we send a CONNECT packet, and then while waiting for the CONNACK response, we declare what to do in case we get a CONNACK packet. It seems a bit risky to me, especially with bigger code, the CONNACK could arrive before we decide what to do with it and it could be ignored, thus skipping the subscriptions part !

This could cause #1153 for example.

I posted a question on stackoverflow : https://stackoverflow.com/questions/75548005/nodejs-mqtt-connection-and-callback-order-is-wrong/76229305?noredirect=1#comment134428767_76229305 but I got no satisfactory answers.

[robertsLando]

MQTT 5.0.0 BETA is now available! Try it out and give us feedback: npm i mqtt@beta. It may fix your issues

Now you can do this by using the manualConnect option and calling connect method right after creating it.