The script starts with web\index.html, where a component with the name pol-map is imported through the following line:

<link rel="import"href="pol_map.html">

From this code, we know that the component is defined in pol_map.html, and the code behind it is in a file named pol_map.dart. For a discussion of the other tags, see the first recipe.

We define a map companies, which we want to display in the file pol_map.dart:

import'dart:html';
import'package:polymer/polymer.dart';

@CustomTag('pol-map')
classPolmap extends PolymerElement {
Map companies = toObservable({1: 'Google', 2: 'Microsoft'});
Polmap.created() : super.created() {
  companies[3] = 'HP';
}

addcompanies(Event e, var detail, Node target) {
  companies[4] = 'Facebook';
  companies[5] = 'Apple';
  }
}

The structure of the Polymer component is outlined in...