Polymer.dart is a port of the JavaScript Polymer library that combines Web Components, the Observe library, and a few others libraries into a single framework. This makes creating reusable encapsulated components very easy (it also uses polymer.js internally).
As we already know enough about Web Components, we'll particularly take a look at one-way / two-way data binding and creating custom elements with their behavior written in Dart.
Note
You might have already seen Dart's Web UI package used in a tutorial, blog, article, or a book. Web UI is an older Dart API, which is deprecated in favor of polymer.dart.
We'll begin by installing polymer.dart by adding polymer among our dependencies in pubspec.yaml and letting Dart Editor fetch all the dependencies for us. Right away, we can tell polymer.dart what our app's entrance points are. These are the pages that the user can access (that's probably everything except HTML templates for our custom...