I explored using client-side service workers for build-less deployment workflows a while back, but the blocker was the initial visit when the service worker hasn't been installed yet. Ended up using es-module-shim's fetch hook (https://github.com/guybedford/es-module-shims#fetch-hook) instead, which worked quite well.

I kept the demo repo around here, in case it's helpful to anyone: https://github.com/lewisl9029/buildless-hot-reload-demo.

The repo itself is quite out of date at this point, but my current project, Reflame, is essentially the spiritual successor: https://reflame.app/

Reflame has the same ideals of achieving the developer experience I've always wanted for building client rendered React apps:

- instant production deployments (usually <200ms)

- instant preview environments that match production in pretty much every imaginable way (including the URL so we don't have to worry about special whitelisting for CORS and whatnot), that can also be flipped into development mode for fast-refresh (for the seamless feedback loop we're used to in local dev) and dev-mode dependencies (for better error messaging, etc)

- close-to-instant browser tests (1-3 seconds) that enable image snapshot comparisons that run with maximum parallelism, and only rerun when their dependency graphs change, and auto flake detection/recovery