Poylmerize - Polymer 2.0 Dart experimental support

This package is a command line tool to build Polymer 2 components with DDC from Dart.

The benefits of this approach compared to the dart2js standard polymer-1.x are :

  • support for polymer 2.0-preview (web components 1.0)
  • using DDC to generate ES6 output code
  • using bazel as build system (see also rules
  • dynamic load of polymer components definitions through requirejs
  • interoperability with other JS frameworks
  • Incremental build (dependencies are built only once)
  • possibility to distribute ONLY the build result to thirdy party users and devs
  • simplified API
    • automatic getter and setter (no explicit notify for first level properties)
    • NO Annotations required to expose properties
    • NO Annotations required to expose methods


Actually this tool will now work only for Linux. To be used on macosx should be only a matter of changing some builtin path and this will be fixed very soon.

Bazel doesn't work on windows system for now (it depends too much un bash to be able to work there) so... sorry guys.


This tool is actually used internally by bazel rules so you don't need to install it (bazel will do that for you). All you have to do is start using bazel rules and enjoy.

If you want to learn more, check out the sample project (see below).


A sample project demostrating how to build polymer-2 components using polymerize can be found here :

See the README for more information.

Component definition

This is a sample component definition:

import 'package:polymer_element/polymer_element.dart';
import 'package:my_component/other_component.dart' show OtherComponent;

class MyTag extends PolymerElement {

  int count = 0;  // <- no need to annotate this !!!

  onClickIt(Event ev,details) {  // <- NO need to annotate this!!!!
    count = count + 1;    // <- no need to call `set` API , magical setter in action here

  void countChanged(val) {
    print("Count has changed : ${count}");

  MyTag() { // <- Use a simple constructor for created callback !!!
    print("HELLO THERE !")

  factory MyTag.tag() => Element.tag('my-tag'); // <- If you want to create it programmatically use this

  connectedCallback() {
    super.connectedCallback(); // <- MUST BE CALLED !!!!

The Html template is just the usual dom-module template without any JS code. Link tags will be automatically generated based on the uses attribute of the @PolymerRegister annotation (BTW : this fixes also the annoying unused import problem with polymer-dart, and also the IDE will help you adding the right import). The index.html should preload requirejs, webcomponents polyfill and polymer.html (see the demo).


After complilation everything will be found in the bazel output folder, ready to be used


  • more polymer APIs
  • better convert to/from JS
  • annotations for properties (computed props, etc.)
  • support for mixins
  • ~~support for external element wrappers~~
  • ~~support for auto gen HTML imports~~