Register Child Components for Communication

components.deprecation-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'li',
  isExpanded: true,
  registerItem: 'registerItem',
  init(){
    this._super( ...arguments );
    this.sendAction('registerItem', this);
  },
  click(){
    this.toggleProperty('isExpanded');
  },
  actions: {
    expand(){
    	this.set('isExpanded', true);
    },
    collapse(){
    	this.set('isExpanded', false);
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  deprecationItems: [],
  deprecations: [
  	'foo',
    'bar',
    'baz'
  ],
  actions: {
  	registerItem(component) {
      this.get('deprecationItems').pushObject(component);
    },
    expandAll() {
      this.get('deprecationItems').forEach(component => {
        component.send('expand');
      });
    },
    collapseAll() {
      this.get('deprecationItems').forEach(component => {
        component.send('collapse');
      });
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<button {{action "expandAll"}}>Expand All</button>
<button {{action "collapseAll"}}>Collapse All</button>
<br>
<ul>
  {{#each deprecations as |deprecation|}}
  	{{#deprecation-item}}
      {{deprecation}}
    {{/deprecation-item}}
  {{/each}}
</ul>

templates.components.deprecation-item.hbs

{{yield}} - {{if isExpanded "Expanded" "Collapsed"}}

twiddle.json

{
  "version": "0.10.7",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.0",
    "ember-data": "2.10.0",
    "ember-template-compiler": "2.10.0",
    "ember-testing": "2.10.0"
  },
  "addons": {}
}