Observer Bug

controllers.application.js

import Ember from 'ember';

let Person = Ember.Object.extend({
  notificationService: Ember.inject.service(),
  firstName: null,
  lastName: null,
  
  fullName: Ember.computed('firstName', 'lastName', function() {
    return `${this.get('firstName')} ${this.get('lastName')}`;
  })
});

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  firstName: 'John',
  lastName: 'Doe',
  person: null,

  notificationService: Ember.inject.service(),
  
  init() {
  	this._super(...arguments);
    let person = new Person({
			firstName: this.get('firstName'),
      lastName: this.get('lastName')
		});
    
    this.set('person', person);
    
    this.get('notificationService')
      	.sendNotification('All set up');
  },
  
  partOfNameChanged: Ember.observer('person.firstName', 'person.lastName', function() {
    this.get('notificationService')
        .sendNotification(
      		`Person's name changed to 
					 ${this.get('person.fullName')}`
    		);
  }),
  
  actions: {
  	updateName() {
      let { firstName, lastName } = this.getProperties('firstName', 'lastName');
      let personService = this.get('personService');
      
      this.set('person.firstName', firstName);
      this.set('person.lastName', lastName);
    }
	}
});

services.notification-service.js

import Ember from 'ember';

export default Ember.Service.extend({
  messages: null,
  init() {
    this.set('messages', []);
  },
  sendNotification(message) {
    this.get('messages').pushObject(message);
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
Person full name: {{person.fullName}}
<br>
<br>
<ul>
	{{#each notificationService.messages as |message|}}
		<li>{{message}}</li>
	{{/each}}
</ul>

{{input type="text" value=firstName}}
{{input type="text" value=lastName}}
<br>
<button type="button" {{action "updateName"}}>
  Update Name
</button>

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember-template-compiler.js"
  }
}