To create a web page that will run Narya in a browser, you will need the JavaScript package manager npm. Once you have this, run the following commands:
opam install zarith_stubs_js
cd narya
dune build js/jsnarya.bc.js
cd js
npm install webpack
npm run build
Now place the files js/dist/index.html, js/dist/bundle.js, and _build/default/js/jsnarya.bc.js in a directory that will be served by a web server. For instance, to test it locally, you can run:
cd dist
ln -s ../../_build/default/js/jsnarya.bc.js .
npx http-server . -o -p 9999
With this, changes to the OCaml code will take effect as soon as you re-run dune build js/jsnarya.bc.js and reload the web page, while changes to the JavaScript side (src/main.js) will take effect as soon as you re-run npm run build and reload the web page.