Support for the Web

Flutter has revolutionized the way developers build cross-platform applications, extending its capabilities beyond mobile to web platforms. This article aims to understand Flutter's web support, breaking down the complex architecture into easy-to-understand concepts for beginners.

Introduction to Flutter Web Support

Flutter is a powerful framework that allows developers to create beautiful, natively compiled applications from a single codebase. It is known for its ability to run on various platforms, including iOS, Android, and now, the web. The integration of Flutter with web technologies marks a significant milestone, offering developers the tools to craft high-performance, rich web applications.


At the core of Flutter's web support is Dart, a modern programming language developed by Google. Dart is unique because it can compile into JavaScript, the language of the web. This capability is crucial for Flutter's operation on web platforms, as it allows Dart code to run in web browsers seamlessly. Dart's design focuses on both development and production needs, ensuring that apps are not only easy to build but also optimized for performance.

Flutter Engine and Web Browsers

The Flutter engine, originally written in C++, is designed to interact with the underlying operating system of a device. However, this approach does not directly apply to web browsers. To bridge this gap, Flutter introduces a web-specific engine implementation that leverages standard browser APIs. This adaptation enables Flutter apps to run on the web without losing their rich features and responsive design.

Rendering Options: HTML and WebGL

Flutter offers two modes for rendering content on the web:

  • HTML Mode: Utilises familiar web technologies like HTML, CSS, Canvas, and SVG. This mode is optimised for code size, ensuring quicker load times and efficient performance on web platforms.

  • WebGL Mode (CanvasKit): Employs a WebAssembly-compiled version of Skia (CanvasKit) to achieve direct access to the browser's graphics capabilities. Although this mode results in larger app sizes, it delivers superior graphics performance and fidelity, closely mirroring the experience on native platforms.

Development and Production Workflow

Flutter simplifies the development process with tools tailored for both stages:

  • Development: During the build phase, Flutter uses the dartdevc compiler, which supports incremental compilation. This feature enables the hot restart of web apps, facilitating rapid development cycles.

  • Production: For deploying apps to the web, Flutter switches to the dart2js compiler. This highly optimized compiler packages the Flutter framework, application code, and dependencies into a compact, minified JavaScript file. This process ensures that the final product is ready for efficient deployment and performance on web servers.

Key Takeaways

  • Flutter Web Support: Enables the creation of high-quality web applications using the Flutter framework, extending its cross-platform capabilities.

  • Dart and JavaScript: Dart's ability to compile into JavaScript is foundational to running Flutter apps on the web, bridging the gap between Flutter's architecture and web technologies.

  • Rendering Modes: Flutter provides flexibility with HTML and WebGL rendering options, balancing between code size efficiency and graphical performance.

  • Development to Production: Flutter streamlines the workflow with distinct tools for development (dartdevc) and production (dart2js), ensuring that web apps are both easy to develop and optimized for deployment.

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