New Twiddle

components.my-component\.js

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';

export default class extends Component {
  @tracked value;
  @tracked _previousValue;

  constructor(owner, args) {
    super(...arguments);

    this.updateValue(args.value);  
  }

  @action
  updateValue(newValue) {
    this._previousValue = this.value || 'none';
    this.value = newValue;
  }
  
  @action foo() {
    this.updateValue(777);  
  }
}

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
{{outlet}}
<br>
{{my-component value=4}}
<br>

templates.components.my-component\.hbs

{{this.value}} {{this._previousValue}}
<button {{action "foo"}}>FOO</button>

twiddle\.json

{
  "version": "0.17.1",
  "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/3.5.1/jquery.js",
    "ember": "3.22.0",
    "ember-template-compiler": "3.22.0",
    "ember-testing": "3.22.0"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}