Cross-Platform JavaScript App Prototype

I need a small proof-of-concept that shows JavaScript can drive one codebase across web, mobile, and desktop. The scope is intentionally lean: break ground on the project, wire up navigation, and give me something I can run everywhere with minimal setup.

Here’s what I’m after:

• Web build that loads in any modern browser.
• Mobile builds for both iOS and Android.
• Desktop wrapper (Electron or similar) for Windows/macOS.
• One sample screen illustrating data input, basic state management, and simple routing.
• Clear, step-by-step instructions so I can install dependencies, run, and build each target myself.
• Clean, commented source code stored in a Git repo.

Use whichever JavaScript stack you find efficient—React with React Native and Electron, Ionic + Capacitor, or an equivalent toolkit—as long as it stays open-source and I can extend it later.

Design can remain bare-bones; functionality and clarity come first. Tell me:

1. The framework you propose.
2. How quickly you can deliver this starter.
3. A link to any similar cross-platform boilerplate or app you’ve created.

I’m looking for concise, working code and straightforward communication.