ember.js#12080

components.child-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  _willDestroyElement: Ember.on('willDestroyElement', function() {
   	Ember.assert('parentView undefined on willDestroyElement event', !Ember.isEmpty(this.get('parentView'))); 
  })
});

components.parent-component.js

import Ember from 'ember';

export default Ember.Component.extend({
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  actions: {
    toggle(property) {
      this.incrementProperty(`${property}Toggled`);
      this.toggleProperty(property);
    }
  },
  appName: 'Ember Twiddle',
  simple: true,
  simpleToggled: 0,
  ifInside: true,
  ifInsideToggled: 0,
  ifOutside: true,
  ifOutsideToggled: 0
});

templates.application.hbs

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

<h2>parentView is undefined on second call of willDestroyElement</h2>
<p>toggled {{simpleToggled}} times</p>
<p>
	{{#if simple}}
    {{child-component}}
  {{/if}}
  <button {{action 'toggle' 'simple'}}>toggle</button>
</p>

<h2>parentView is never undefined</h2>
<p>toggled {{ifOutsideToggled}} times</p>
<p>
  {{#if ifOutside}}
    {{#parent-component}}
      {{child-component}}
    {{/parent-component}}
  {{/if}}
  <button {{action 'toggle' 'ifOutside'}}>toggle</button>
</p>

<h2>parentView is undefined on first call of willDestroyElement</h2>
<p>toggled {{ifInsideToggled}} times</p>
<p>
  {{#parent-component}}
    {{#if ifInside}}
      {{child-component}}
    {{/if}}
  {{/parent-component}}
  <button {{action 'toggle' 'ifInside'}}>toggle</button>
</p>

templates.components.child-component.hbs

parent view: {{parentView.elementId}}

templates.components.parent-component.hbs

{{yield}}

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}