New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
});

components.my-component2.js

import Ember from 'ember';

export default Ember.Component.extend({
});

controllers.application.js

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

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  appNameJSON: computed('appName', function() {
    return JSON.stringify(this.appName)
  }),
  
  value: true
});

templates.application.hbs

<p>{ {my-component text="mut inside" click=(action (mut appName "newName"))} }</p>
{{my-component text="mut inside" click=(action (mut appName "newName"))}}
<p>{ {my-component click=(action (mut appName) "newName")} }</p>
{{my-component text="mut outside" click=(action (mut appName) "newName")}}

<b>Name: </b>
<p>{{appName}}</p>

<b>JSONized Name:</b>
<p>{{appNameJSON}}</p>

{{my-component2 text="Wrong way" clickAction=(action (mut value false))}}
{{my-component2 text="Right way" clickAction=(action (mut value) false)}}

Value: {{value}}

templates.components.my-component.hbs

<button>{{text}}</button>

templates.components.my-component2.hbs

<button {{action clickAction}}>{{text}}</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"
  }
}