Computed properties

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  obj: {},
  
  fi: Ember.computed('obj.fi', function() {
    return this.get('obj.fi');
  }),
  
  fai: Ember.computed('obj.fai', function() {
    let fai = this.get('obj.fai');
    console.log('fai> ', fai);
    return fai;
  }),
  
  fifai: Ember.computed('obj', function() {
    let obj = this.get('obj');
    return obj.fi + obj.fai;
  }),
  
  actions: {
    newObject: function() {
      let obj = {
        fi: 'a', fai: 'b'
      };
      this.set('obj', obj);
    },
    deleteFai: function() {
      this.set('obj.fai', null);
    }
  }
  
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
fi: [{{fi}}]
<br>
fai: [{{fai}}]
<br>
fifai: [{{fifai}}]
<br>
<br>

<button {{action "newObject"}}>
  new object
</button>

<button {{action "deleteFai"}}>
  delete fai
</button>

{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}