$ dune build --verbose
cd _build/default/bin/web
# Just calls js_of_ocaml against `bench.bc`. Note that "--opt 3" is NOT passed.
js_of_ocaml -o bench.bc.js /home/lin/.opam/4.13.1/lib/bigstringaf/runtime.js bench.bc
$ dune build --profile release --verbose
cd _build/default/bin/web