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

MɑԵհeմՏ ѵíղícíմՏ — Tue, 12 May 2026 00:48:47 +0000

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:

mathOS Live: https://matheusvinicius.dev.br/
The Package: https://pub.dev/packages/flutter_lazy_load_web
GitHub Repo: https://github.com/Mathvdias/portfolio

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