in 4.0 the request cycle is totally open: you can replace the fetch() implementation on a per-request basis

learned that trick from fixi.js

Yep, it's super nice. The Service Workers API also makes this really easy too. I experimented with compiling a Rust Axum server to WASM and then ran it in my service worker. Also, thanks for incorporating fetch into htmx!

I thought I'd include an example of replacing fetch for anyone that come across this.

    const originalFetch = window.fetch;
    window.fetch = function(url, options) {
      if (url.includes('/api/user')) {
        const mockUser = {id: 1, name: 'John Doe', email: 'john@example.com'};
        return Promise.resolve(new Response(JSON.stringify(mockUser)));
      }
      return originalFetch(url, options);
    };