Yes, Python, Ruby and JavaScript have better MQTT libraries. I managed to write an async Perl client using POE (the networking code was already heavily using it, otherwise I wouldn't even pick POE since it's awful and also dead) and Net::MQTT::Message. Piping output into mosquitto_pub/sub was out of the question, since this was no hack but rather a service that streams data into the broker.

I suspect writing it in Ruby with async would also prove problematic, but there are the ruby-mqtt and async-io gems and one would use the MQTT::Packet for formatting messages and Async::IO for the networking code. Still a lot less painful than what I did with POE and Net::MQTT::Message.

MQTT.js is async already, you just import and use it in the browser, Node.js, probably Deno as well. Easy. It took literally five minutes to get the client enpoint working in the browser over WebSockets. One could even do it from the browser console.