New Twiddle

components.my-component.js

import Ember from 'ember';
import { computed } from '@ember/object';

let count = 0;

export default Ember.Component.extend({
  count: computed('value', () => count++),

  value: computed({
    get() {
      return this._value + 'baz';
    },

    set(key, value) {
      this._value = value;
      return this._value + 'baz';
    },
  }),
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

{{this.value}}

<MyComponent @value={{this.value}} />

templates.components.my-component.hbs

{{this.value}}
<button {{action (mut @value) this.count}}>
  Update Named Arg
</button>
<button {{action (mut this.value) this.count}}>
  Update Property
</button>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}