There's a communication channel between the Rust code and the JS running in the browser. It's possible to move as much functionality to Rust as you want... It's

There's a communication channel between the Rust code and the JS running in the browser. It's possible to move as much functionality to Rust as you want... It's even possible to compile Rust to WASM to use that in the "frontend" though that from my experience is very cumbersome due to the Rust bindings for the Web API being pretty terrible.