Browsers can do surprisingly much even if you don't have a internet connection. Couple local networks (even local-only networks) with browser being able to communicate them, and you can build local-first applications with just JS in the browser.

In the case of IPFS, you can have a IPFS node running locally, have a browser client communicate with it and just store the latest hash of your state (that you can backup outside of the browser too). So if the local state (in the browser) gets lost, you can restore it from the hash. Often used content can be cached in the browser but still stored in your IPFS node.