New Twiddle

components.inapp-alert-manager.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  inAppAlert: Ember.computed.readOnly('inAppAlertQueue.firstObject'),
  
  init() {
    this._super(...arguments);
    this.set('inAppAlertQueue', [
      'hello',
      'ben',
      'it',
      'was',
      'good',
      'talking',
      'with',
      'you'
   	].map(message => ({
      message
    })));
  },
  
  actions: {
    dismissAlert() {
      this.get('inAppAlertQueue').shiftObject();
    }
  }
});

components.inapp-alert.js

import Ember from 'ember';

export default Ember.Component.extend({
  didRender() {
    setTimeout(() => Ember.tryInvoke(this, 'onDismiss'), 1000);
  }
});

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}}
<br>
<br>

templates.components.inapp-alert-manager.hbs

Alert Manager
{{#if inAppAlert}}
  {{inapp-alert
  	alert=inAppAlert
    onDismiss=(action "dismissAlert")}}
{{/if}}

templates.components.inapp-alert.hbs

Message: {{alert.message}}

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"
  }
}