Computed Property at runtime

controllers.application.js

import Ember from 'ember';

const {
  computed: { collect, reads },
  defineProperty,
  mixin,
  propertyDidChange,
  propertyWillChange,
  run: { later },
  set
} = Ember;

function forceSet(obj, keyName, value) {
  propertyWillChange(obj, keyName);
  defineProperty(obj, keyName, value);
  propertyDidChange(obj, keyName);
  return value;
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',

  country: 'America',
  description: 'land of the free',
  
  init() {
    later(() => {
      // set(this, 'appName', collect('country', 'description'));
      // defineProperty(this, 'appName', collect('country', 'description'));
      // mixin(this, { appName: collect('country', 'description') });
      // this.appName = collect('country', 'description'); // Assertion Failed: You must use Ember.set() to set the...
      forceSet(this, 'appName', collect('country', 'description'));
    }, 2000);
    
    later(() => {
      set(this, 'description', 'land of the cinnabon');
    }, 4000);

    later(() => {
      // set(this, 'appName', reads('country')); // crashes
      // defineProperty(this, 'appName', reads('country'));
      // mixin(this, { appName: reads('country') });
      // this.appName = reads('country'); // Assertion Failed: You must use Ember.set() to set the...
      forceSet(this, 'appName', reads('country'));
    }, 6000);
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

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"
  }
}