New Twiddle

components.inapp-alert-manager.js

import Ember from 'ember';

export default Ember.Component.extend({
  inappAlert: Ember.computed.readOnly('liveAlertsQueue.firstObject'),
  init() {
    this._super(...arguments);
    this.set('liveAlertsQueue', []);
  },
  
  // This just fakes putting a queue on after the component is rendered
  // I wanted to make sure changing `liveAlertsQueue` worked
  didRender() {
    setTimeout(() => {
      this.get('liveAlertsQueue').pushObject(true);
    }, 1000);
  }
});

components.inapp-alert.js

import Ember from 'ember';

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

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#inapp-alert-manager as |alertManager|}}
  {{#if alertManager.inappAlert}}
    Hello Ben
  {{/if}}
{{/inapp-alert-manager}}
<br>
<br>

templates.components.inapp-alert-manager.hbs

{{yield (hash
  inappAlert=inappAlert
)}}

templates.components.inapp-alert.hbs

{{yield}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}