New Twiddle

components.child\.js

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

export default class extends Component {
  @tracked
  newDev = "";
  
  @action
  onChange (e) {
    this.newDev = e.target.value;
  }
}

components.parent\.js

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

export default class extends Component {
  @tracked devArray = ['Jason', 'Scott', 'Edgar', 'Elias'];

	@action
	addNewDev (dev) {
    this.devArray = [...this.devArray, dev];
  }

}

controllers.application\.js

import Controller from '@ember/controller';

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

templates.application\.hbs

<Parent />

templates.components.child\.hbs

<ul>
{{#each @devs as |dev|}}
	<li>{{dev}}</li>
{{/each}}
</ul>
<input type="text" value={{this.newDev}} onchange={{fn this.onChange}} />
<button {{on "click" (fn @updateDevList this.newDev)}}>
	Add Dev
</button>

templates.components.parent\.hbs

<h1>List of Devs</h1>
<Child @devs={{this.devArray}} @updateDevList={{this.addNewDev}}/>

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": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}