Best Practices for Optimizing Flutter Web Loading Speed
Article Summary
Cheng Lin from Google's Flutter team tackles the elephant in the room: Flutter web apps are slow to load. Here's how to fix it.
Flutter web apps face loading speed challenges that can kill user experience before it even starts. Cheng Lin, a Product Manager working with Google's Flutter team, breaks down practical optimization strategies covering everything from rendering engines to caching mechanisms.
Key Takeaways
- Wasm rendering reduces app size and starts faster than JavaScript
- AVIF compression shrinks images from 319 KB to 10 KB with minimal quality loss
- Deferred imports split code to load only what users need immediately
- Unawaited functions let UI render before costly operations complete
- Perceived speed matters more than actual speed use splash screens
Flutter web performance requires balancing technical optimizations (Wasm, lazy loading, modern image formats) with perception tricks (splash screens, preloading) to make apps feel fast.
About This Article
CanvasKit, Flutter web's default renderer, adds 1.5 MB to your app size and slows down startup. All widgets have to wait for the full file to load before they become interactive.
Cheng Lin suggests switching to WebAssembly rendering mode instead. This removes the dart:html dependency and uses the web package with dart2wasm, which starts up faster than JavaScript.
Browsers cache Wasm modules as compiled native code, so they load at speeds comparable to native binaries. There's no need for reparsing, recompilation, or the JIT processing that JavaScript requires.