A web framework for Dart based on Flutter's widget model. The goal of the project is conceptual and data model compatibility with Flutter. An explicit non-goal is "write once, run anywhere". Butterfly shares no code with Flutter.

Disclaimer: This is a personal experiment. This is not an official Google product.

What is Butterfly?

  • Object-oriented
  • Widget-based (i.e. component-based)
  • Reactive
  • Web framework
  • For Dart
  • Inspired by Flutter (transitively by ReactJS)

Who is Butterfly for?

  • For app developers who build mobile apps using Flutter, and who also need to build web apps. Butterfly gives you a single conceptual model for writing your apps for both web and mobile, and allows the reuse of big chunks of code.

  • For web developers, switching to Dart but prefer using a ReactJS-like app framework.

  • For application developers who prefer functional-reactive programming style.

Why Butterfly?

  • One language: traditionally web-frameworks make developers work in a number of languages that are glued together by toolchains and runtimes. The common combination is JavaScript, HTML templates and CSS (or SASS, or LESS). This complicates tooling and usually the integration between the languages is very weak. Butterfly gives you one modern battle-tested language - Dart - that proved to scale from small apps to large enterprise projects, has great tools and is a pleasure to write code in every day. Code navigation works seamlessly, typos in the code are identified immediately, and you get powerful refactoring features, such as renaming variables and methods. In addition Dart gives you minification, dead code elimination and performance optimizing compiler. Having one powerful language lets you write your code using the normal OOP practices and patterns:

  • Encapsulation: private fields, methods and classes
  • Lexical scoping: static and top-level variables, constants and functions

  • Control of API surface: make your components private
  • Control of initialization and lifecycle: components can be cached, injected, shared, and provided via factories

  • Debugging: breakpoints work everywhere and show correct stack information.
  • Familiar: if you have prior Flutter/ReactJS experience you will feel right at home.

  • Reusable: while not API compatible with Flutter (on purpose), the component system is identical, which means you can reuse most of your app's business logic, data model and utilities across mobile and web. More importantly, you will be using the same Dart tools both for your mobile and web projects. You cannot reuse the widgets though, as they are targeting different rendering systems (Flutter Engine vs HTML DOM).

  • Simple: Butterfly introduces only a handful of concepts popularized by ReactJS and it works like a plain library that you can drop into an existing project; it shares all the same Dart libraries so the incremental cost of adding it to your project is minimal.

  • Small: starting application size is <40kb (minified + gzipped)
  • Fast: while it's hard to compare frameworks in terms of raw speed, this framework does aim to give you great levels of control for efficient incremental UI updates. Because widgets in Butterfly are plain in-memory objects (a.k.a. virtual) the framework minimizes the number of DOM nodes by only creates nodes for those virtual nodes that need them. Most other frameworks create a DOM element for each component.

  • Layered: made of layers (widgets, tree, DOM) - you choose how low-level to go.

  • Hackable: defining new widgets is at the core of the development experience. However, you can also extend the virtual tree model when you need to perform advanced rendering tricks directly on top of the DOM API.