Why Wasm is a Game-Changer for Flutter Web

Koen Van Looveren


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WebAssembly (Wasm is short) is transforming the web development landscape, and its integration with the Flutter framework is particularly groundbreaking. By allowing code to run at near-native speed in browsers, Wasm brings a lot of benefits that significantly enhance Flutter's capabilities.

Practical Applications and Future Prospects

The integration of WebAssembly with Flutter opens up numerous practical applications. For instance, complex game development and high-performance data visualisation can now be more efficiently implemented within Flutter web apps. As WebAssembly continues to evolve, we can expect even more optimisations and features that will further enhance its synergy with Flutter.

Six Reasons Why WebAssembly is Important for Flutter

  1. Near-Native Performance: One of the primary advantages of WebAssembly is its ability to execute code at speeds comparable to native applications. This is crucial for Flutter, which aims to provide a seamless and performant user experience across platforms. Wasm achieves this by compiling code into a compact binary format that can be executed directly by the browser's JavaScript engine, bypassing the slower interpretation processes typically associated with JavaScript.
  2. Enhanced User Experience: With WebAssembly, Flutter applications can offer richer, more complex interactions without compromising on speed or responsiveness. This is particularly beneficial for applications that demand high performance, such as those with heavy graphical content or real-time data processing.
  3. Cross-Platform Efficiency: Flutter's promise of "write once, run anywhere" is further bolstered by WebAssembly. Developers can write their applications in Dart, compile to Wasm, and run them efficiently in any modern browser. This reduces the need for multiple codebases and simplifies the deployment process.
  4. Improved Load Times: Wasm modules are typically smaller and load faster than equivalent JavaScript code. This means Flutter applications can start up more quickly, providing a better initial user experience and reducing the time users spend waiting for the application to become interactive.
  5. Security:WebAssembly runs in a secure, sandboxed environment, isolating it from the rest of the browser. This adds an extra layer of security, protecting both the application and the user's device from potential exploits and vulnerabilities.
  6. Interoperability: Wasm's design allows it to interact seamlessly with JavaScript. Flutter applications can thus leverage existing JavaScript libraries and frameworks, extending their functionality without sacrificing performance.

A Real Flutter Web Comparison

When considering how WebAssembly enhances Flutter's web capabilities, it's useful to compare different rendering options:

HTML Renderer

  • Suitable for simple web applications.
  • Native text rendering
  • Limited performance compared to more advanced options.

CanvasKit (JS)

  • JavaScript-based rendering engine.
  • Provides better performance and visual fidelity than the HTML renderer but still relies on JavaScript.

CanvasKit (Wasm)

  • WebAssembly-based rendering engine.
  • Offers the best performance and visual fidelity, leveraging the speed and efficiency of WebAssembly.

Getting Started with WebAssembly in Flutter

To get started with WebAssembly in Flutter, developers can refer to the comprehensive resources available on Flutter's WebAssembly documentation. This documentation provides detailed guidance on setting up, compiling, and integrating Wasm with Flutter projects.

Update your project

To have the best experience with WebAssembly make sure you are on the latest Flutter version. Starting from Flutter 3.22.0 Wasm is added to the stable Flutter channel. There are a couple of things to consider before you can build your app with Wasm. Some dependencies should be changed to support Wsam. If you are an early adopter you might find that not all dependencies have already updated to dart:web. Create a github issue or even better support the community by doing the update yourself and creating a pull request.


Make sure you update dart:html to dart:web everywhere.

dart:js or package:js

Another package you should update is dart:js or package:js, this should be updated to dart:js_interop

Build your web app

Now you can bulid your app with Wasm and deploy to your favorite hosting service

flutter build web --wasm

Start testing

Now you can start testing on a compatible browser.

  • Why Not Firefox? Although Firefox versions 120 and later were previously capable of running Flutter/Wasm, a current bug is hindering compatibility with Wasm.
  • Why Not Safari? Safari does not yet support WasmGC. Progress on this implementation can be tracked through a specific bug report.
  • Why Not on iOS? Flutter compiled to Wasm cannot run on any browser version on iOS. This is because all iOS browsers are mandated to use WebKit and are unable to employ their own browser engines.

Because these bugs might get fixed in the future. Check the Wasm Flutter documention on these issues.


WebAssembly is not just a performance booster for Flutter; it's a pivotal technology that unlocks new potential for web applications, making them faster, more secure, and highly efficient. By embracing Wasm, Flutter developers can stay ahead of the curve, delivering exceptional web experiences that rival native applications.

Still not convinced that Flutter can be a good fit for your web project? Check out how Flutter compares to other web frameworks to see the full scope of its capabilities. Embrace the future of web development with Flutter and WebAssembly, and deliver experiences that set your applications apart from the rest.

Still not convinced that Flutter can be a good fit for your web project? Check out how Flutter compares to "actual web frameworks"

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