Ember.js: declaring a computed property/observer with prototype extension - http://blog.ksol.fr/ember-js-declaring-computed-property-and-observers/

gistfile1.js

export default Ember.Object.extend({
  firstName: "Bob",
  lastName: "Jones",
  fullName: function() {
    return `${this.get('firstName')} ${this.get('lastName')}`;
  }.property('firstName', 'lastName'),
  nameHasChanged: function() {
    console.log(`name has changed! Now it is ${this.get('fullName')}`);
  }.observes('fullName')
});