The developer docs are here: https://conversejs.org/docs/html/development.html
See also AGENTS.md which has useful information even for humans.
npm install
npm run serve &
npm run watch
Go to http://localhost:8000/dev.html
Then modify dev.html so that converse.initialize() is called with relevant settings.
Webpack will "watch" the source files and automatically recreate the build if they are modified. So you don't have to do anything to rebuild whenever you've change something in a file but you will have to manually reload the browser tab to see the changes in the browser.
If you want to have live reloading whenever any of the source files change, you
can run make devserver (or npm run devserver).
Then go to http://localhost:8080
Then modify webpack.html so that converse.initialize() is called with relevant settings.