This is the "hello world" program from https://bfnightly.bracketproductions.com/rustbook/chapter_1.html.
To build it for web, run (on Windows):
cargo build --release --target wasm32-unknown-unknown
wasm-bindgen .\target\wasm32-unknown-unknown\release\hello-bracket.wasm --out-dir wasm --no-modules --no-typescript
To serve it locally, run:
cargo install http-server
http-server wasm
See https://bfnightly.bracketproductions.com/rustbook/webbuild.html for more details.