New Twiddle

controllers.application.js

import Ember from 'ember';
const {computed} = Ember;

let aCount = 0;
let bCount = 0;

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  value: 'initial',
  
  neverChangingProperty: computed('value', function() {
    return 'always the same';
  }),
 
  a: computed('neverChangingProperty', function() {
    aCount += 1;
    return aCount;
  }),

  b: computed('value', function() {
    bCount += 1;
    return bCount;
  }),
  
  actions: {
    updateValue() {
      this.set('value', Math.random())
    }
  }
  
});

templates.application.hbs

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

a: {{a}}
<br>
b: {{b}}
<br>
value: {{value}}

<button {{action 'updateValue'}}>Update value</button>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}