Computed Component

components.my-component-help.js

import Ember from 'ember'

export default Ember.Component.extend({
  tagName: 'button',
  classNames: ['navigation', 'user-menu'],
  myService: Ember.inject.service('my-service'),
  contexts: Ember.computed.readOnly('myService.contexts'),
  actions: {
    openHelp(){
      console.log(this.get('contexts'))
      alert(this.get('contexts'))
    }
  }
});

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  myService: Ember.inject.service('my-service'),
  didInsertElement() {
    // avoid deprecation warning about setting properties in didInsertElement
    Ember.run.scheduleOnce('afterRender', () => {
      this.get('myService').addContext(this.get('value'));
    });
  },
  willDestroyElement() {
    this.get('myService').removeContext(this.get('value'))
  },
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

services.my-service.js

import Ember from 'ember';

export default Ember.Service.extend({
  contexts: [],
  addContext(context) {
    this.get('contexts').pushObject(context);
  },
  removeContext(context) {
    this.get('contexts').removeObject(context);
  },
  getContext() {
    return this.get('contexts');
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{my-component-help}}
<br>
{{outlet}}
<br>
{{my-component value='Test'}}
{{my-component value='Test2'}}
<br>

templates.components.my-component-help.hbs

<button {{action 'openHelp'}}>Test</button>

<ul>
{{#each contexts as |context|}}
  <li>{{context}}</li>
{{/each}}
</ul>

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember-template-compiler.js"
  }
}