octane + computed

controllers.application\.js

import Controller from '@ember/controller';
import EmberObject, { action, computed } from '@ember/object';

let FakeModel = EmberObject.extend({
  bar: 1,
  foo: computed.readOnly('bar'),
});

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
	bob = FakeModel.create();

	get fizz() {
    return this.bob.foo;
  }

	@action
  doIncrement() {
    this.bob.incrementProperty('bar');
  }
}

templates.application\.hbs

<h1>testing 1, 2, 3</h1>

<dl>
  <dt>foo</dt>
  <dd>{{this.bob.foo}}</dd>
  
  <dt>bar</dt>
  <dd>{{this.bob.bar}}</dd>
  
  <dt>fizz</dt>
  <dd>{{this.fizz}}</dd>
</dl>

<button {{on "click" this.doIncrement}}>Increment</button>

twiddle\.json

{
  "version": "0.17.0",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.16.3",
    "ember-template-compiler": "3.16.3",
    "ember-testing": "3.16.3"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}