This repository demonstrates a bug in @tanstack/react-start's createIsomorphicFn when used with Cloudflare Workers.

When createIsomorphicFn() is called at module top-level, it returns a function instead of the expected value. However, when called inside a component, it works correctly.

Related issue: TanStack/router#6217

const getEnvironment = createIsomorphicFn()
  .server(() => "server")
  .client(() => "client");

const value = getEnvironment();
// Expected: "server" during SSR, "client" on client
// Actual: [Function] at module level

1. Clone this repository
2. Install dependencies:

   pnpm install

3. Start dev server:

   pnpm dev

4. Open http://localhost:5173
5. Observe the console output and page content

• @tanstack/react-start: 1.143.6
• @cloudflare/vite-plugin: 1.0.0+
• Vite: 7.0.0
• Node.js: 22.x