Stupid-simple, low-level Web application library built with Incremental DOM and html_builder. Somewhat comparable to React.

Mariposa offers no state management; this is by design. Handling state should be handled via dart:async, Redux, or some other mechanism. Calling for a re-render is not memory-intensive, thanks to Incremental DOM.

Thanks to libraries like zen and html_builder/elements.dart, it is possible to cleanly build HTML AST's with a Dart DSL that looks exactly like an HTML AST.


The most simple example:

import 'dart:html' hide Node;
import 'package:html_builder/elements.dart';
import 'package:html_builder/html_builder.dart';
import 'package:mariposa/dom.dart' as mariposa_dom;

Node greeting({String message}) => b(c: [text(message)]);

void main() {
    () => greeting(message: 'Hello!'),

This is a super-small example of an application without state. See web/main.dart for an example of an application with state. Complex applications should consider dart:async, Redux, Flux, or some similar state management architecture to create manageable applications.


Note: Not the same as Flutter widgets.

In real-world applications, oftentimes one will need to interact with the state of the DOM, or whatever tree is being rendered.

For this, create a Widget. Not only can widgets be rendered like normal nodes, but upon rendering, their afterRender method is called. Right before destruction, beforeDestroy is invoked.

Both methods are passed an AbstractElement, which prevents a platform-agnostic way to handle events, perform query selectors, and other things. Abstract elements always provide a handle to the nativeElement.

This makes it possible to manage the state of a specific node in the tree, among other things.

import 'dart:io';
import 'package:html_builder/html_builder.dart';
import 'package:html_builder/elements.dart';
import 'package:mariposa/dom.dart' as mariposa;

Passing down state and context

Passing state down a stateless tree can become ugly very quickly. However, Mariposa provides a class called ContextAwareWidget, which can interact with a RenderContext, a scoped state handled internally by Mariposa.

The Context class has provisions for dependency injection, so you don't need any hacks to have fully independent, context-aware widgets:

class MyWidget extends ContextAwareWidget {
  Node contextAwareRender(RenderContext ctx) {
    // Return something...

Server-side Rendering

It's easy; in fact, server-side rendering is Mariposa's bread-and-butter. DOM support was added long after string rendering:

import 'dart:io';
import 'package:html_builder/html_builder.dart';
import 'package:html_builder/elements.dart';
import 'package:mariposa/string.dart' as mariposa;

main() async {
  var server = await HttpServer.bind(InternetAddress.loopbackIPv4, 3000);
  print('Listening at http://${server.address.address}:${server.port}');

  await for (var request in server) {
    var html = mariposa.render(myApp());
      ..headers.contentType = ContentType.HTML

Node myApp() {
  return html(c: [
    head(c: [
        name: 'viewport',
        content: 'width=device-width, initial-scale=1',
      title(c: [
        text('Hello, Mariposa!'),
    body(c: [
      h1(c: [
        text('Hello, Mariposa!'),
      i(c: [
        text('Server-side rendering is easy!'),