Volatile

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  firstName: 'John',
  lastName:  'Smith',
  
  fullName: Ember.computed('firstName', 'lastName', function() {
		return this.get('firstName') + ' ' + this.get('lastName');
	}),
  
  volatileFullName: Ember.computed(function() {
		return this.get('firstName') + ' ' + this.get('lastName');
	}).volatile(),
  
  actions: {
   	changeName() {
    	this.set('firstName', 'Thomas');
    },
    resetName() {
     	this.set('firstName', 'John'); 
    },
    alertVolatileName(){
    	alert(this.get('volatileFullName'));
    }
  }
});

templates.application.hbs

First: {{firstName}} 
<br>
Last: {{lastName}}
<br>
Computed full name: {{fullName}}
<br>
Volatile full name: {{volatileFullName}}
<br> <br>
<button {{action 'changeName'}}> Change first name to Thomas </button>
<button {{action 'resetName'}}> Change first name John </button>
<button {{action 'alertVolatileName'}}> alert volatile name </button>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}