New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
    toggle() {
      this.incrementProperty('someState');
      this.toggleProperty('isActive'); 
    }
  }
});

components.my-other-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  wasCleared: false,
  thingsChanged: Em.observer('someState', function() {
    console.log('observer fired');
    if (!this.get('isActive')) {
      this.set('things', []);
      this.set('wasCleared', true);
    }
  })
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  isActive: true,
  things: [1, 2, 3],
  someState: 0
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

{{my-component isActive=isActive someState=someState}}

Number of things: {{things.length}}<br />

{{#if isActive}}
	{{my-other-component isActive=isActive things=things someState=someState}}
{{/if}}
<br>
<br>

templates.components.my-component.hbs

<button {{action 'toggle'}}>Clear things</button>

templates.components.my-other-component.hbs

{{yield}}
Number of things inside {{things.length}}<br />
Was cleared: {{wasCleared}}

twiddle.json

{
  "version": "0.9.3",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "1.12.2",
    "ember-data": "2.6.1",
    "ember-template-compiler": "1.12.2"
  }
}