Computed Properties

application.controller.js

import Ember from 'ember';

const { computed, get, set } = Ember;

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  person: {
  	first: "Roger",
    last: "Rabbit" 
  },
  
  fullName: computed('person.{first,last}', function() {
    let firstName = get(this, 'person.first');
    let lastName = get(this, 'person.last');
    
    return `${firstName} ${lastName}`;
  }),
  
  actions: {
    changeFirstName() {
      set(this, 'person.first', 'Madison');
    },
    
    changeFullName() {
      set(this, 'fullName', 'Arnold Rabbit');
    }   
  }
});

application.template.hbs

<h1>{{fullName}}</h1>
<br>
<br>
This will change one of the computed properties keys.
<br>
<br>
<button onclick={{action "changeFirstName"}}>
 Set Person First Name
</button>
<br>
<br>
<br>
<br>
This will set the computed property to a string value and stop future changes to the watched key from triggering a refresh.
<br>
<br>
<button onclick={{action "changeFullName"}}>
 Set Full Name
</button>

twiddle.json

{
  "version": "0.6.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "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/2.3.1/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.3.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}