rewrite computed property

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  param1: '1',
  param2: '2',
  obj: Em.Object.create({
    p1: 23,
    p2: 34
  }),
  prop1: Em.computed('param1', 'param2', {
    get() {
      return this.get('param1') + ' : ' + this.get('param2');
    },
    set(_, value) {
      return value;
    }
  }),
  prop2: Em.computed('param1', 'param2', function() {
    return this.get('param1') + ' - ' + this.get('param2');
  }),
  prop3: null,
  observerProp3: Em.observer('obj.{p1,p2}', function () {
    this.set('prop3', this.get('obj.p1') + ' , ' + this.get('obj.p2'));
  })
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{input value=param1}}
{{input value=prop1}}
{{input value=prop2}}

<br>
{{prop1}} - ok
<br>
{{prop2}} - fail
<br>
{{input value=obj.p1}}{{input value=obj.p2}} {{input value=prop3}}
{{obj.p1}} - {{obj.p2}}

twiddle.json

{
  "version": "0.13.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}