Dependency Resolution with Events

gistfile1.js

Polymer({
  is: 'x-foo',

  ready() {
    // provides a FooService to descendents
    this.provideInstance('foo-service', new FooService());
  },

  attached() {
    // requests a BarService from an ancestor, re-requests if moved
    let barService = this.requestInstance('bar-service');
  },

  requestInstance(key) {
    let event = this.fire('request-instance', {
      key: key,
    });
    return event.detail.response;
  },
  
  provideInstance(key, instance) {
    this.addEventListener('request-instance', function(e) {
      if (e.detail.key === key) {
        e.detail.response = instance;
      }
    }.bind(this);
  },
  
});