Frontend & browser·Rendering and the browser pipeline
the form still submits when the JavaScript fails to load, because it was a real form pointing at a real endpoint.
Progressive enhancement
Building the working baseline in HTML and treating scripting as an improvement on top rather than a requirement. It costs discipline — the server needs a non-JavaScript path for anything important — and buys resilience against the surprisingly common case of a bundle that never arrives. Framework conventions built around forms and links have quietly made this the default again after a decade of it not being.