This gist explains one way to create a JS browser bundle for async-mqtt

How-to for bundling async-mqtt for the browser.md

How-to on bundling async-mqtt for the browser

mkdir foo
cd foo
npm install async-mqtt
npm install browserify
npm install tinyify
cd node_modules/async-mqtt/
npm install .
npx browserify index.js -p tinyify -s AsyncMqtt >browserAsyncMqtt.js

Show the compressed size to understand likley HTTP transfer size.

gzip <browserAsyncMqtt.js | wc -c

Be sure to only use this bundle with ws or wss URLs in the browser. Others will likey fail