Optimizing computed property recalculation

controllers.application.js

import Ember from 'ember';

// A computed property chain of property(fullName) <- computed(firstName) <- computed(greeting) will 
// always recalculate computed(firstName) and computed(greeting) when property(fullName) changes. 
// This means that computed(greeting) will be recalculated even when computed(firstName) didn't change
// as a result of property(fullName)'s change. If you find yourself stuck in an "unnecessary expensive
// updates" situation, here is something you can do to optimize:
export default Ember.Controller.extend({
  appName: 'Optimizing computed property recalculation',
  
	fullName: '', 
  
  // converting computed(firstName) to an observer-derived property. this has the disadvantage of
  // being calculated eagerly as property(fullName) changes, but has the benefit that all downstream
  // computed properties will not go through unnecessary invalidation when property(fullName) changes.
  firstName: '',
  firstNameObserver: Ember.observer('fullName', function() {
    this.set('firstName', this.get('fullName').split(' ')[0]);
  }).on('init'),
  
  greeting: Ember.computed('firstName', function() {
    this.incrementProperty('count');
    return `Hello ${this.get('firstName')}`;
  }),
  
	count: 0,

});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
Fullname: <input value={{fullName}} oninput={{action (mut fullName) value='target.value'}}>
<br>
Firstname: {{firstName}}
<br>
Greeting: {{greeting}}
<br>
Count: {{count}}

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.0.1",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}