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How I Built a Mini-OS in Flutter Web: Solving the Bundle Size Challenge with WASM

The Vision: mathOS

I’ve always felt that standard "single-page" portfolios were a bit too static. To push the boundaries of Flutter Web and WebAssembly (WASM), I decided to build mathOS—a desktop-inspired environment right in the browser.

It features draggable windows, a Spotlight-style search, and a real-time guestbook. But as every Flutter Web developer knows, with great UI comes a great... bundle size.

The Hurdle: Initial Loading Performance

When I first compiled the project using WASM, the initial bundle was heavier than I liked. In the web world, every second of loading is a lost visitor. I looked for a straightforward deferred (lazy) loading solution that played well with Flutter’s latest rendering engine, but I couldn't find exactly what I needed.

The Solution: Building flutter_lazy_load_web

Instead of compromising on the UI, I decided to build my own solution. I developed and published flutter_lazy_load_web on pub.dev.

What it does:

  • Wraps Dart’s deferred library loading.
  • Splits screens and heavy logic into on-demand chunks.
  • Reduces the initial JS/WASM overhead significantly.

Engineering Excellence

This wasn't just a "weekend project." To ensure it was production-ready, I implemented:

  • 100% Test Coverage: Ensuring that every window and interceptor works as expected.
  • CI/CD Pipeline: Automated testing and deployment on every push.
  • WASM Support: Leveraging the latest performance improvements in the Flutter ecosystem.

Conclusion

Building mathOS taught me that the limitations of a framework are often just opportunities to build new tools for the community.

Check out the live demo and the source code here:

I’d love to hear your thoughts on WASM performance and how you are handling bundle sizes in your own Flutter Web projects

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