New Twiddle

components.my-child-component\.js

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

export default class extends Component {
  @tracked first;
  @tracked somethingPlusTwenty;
  
  @action
  init(){
    this.somethingPlusTwenty = Number(this.args.something) + 20;
  	console.log(this.somethingPlusTwenty)
  }
  
  @action
  changeSomethingPlusTwenty(){
    this.somethingPlusTwenty = event.target.value;
  	console.log(this.somethingPlusTwenty)
  }
}

components.my-component\.js

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

export default class extends Component {
  @tracked something;
  
  constructor(){
  	super(...arguments);
    this.something = 100;
  }
  
  @action
  changeSomething(){
    this.something = event.target.value;
  };
}

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>
<MyComponent/>
<br>
<br>

templates.components.my-child-component\.hbs

<div {{did-insert this.init}} {{did-update this.init @something}}>
  <br>Something {{if @first "first" "second"}} child component + 20 = 
  <input type="number" value={{this.somethingPlusTwenty}} {{on "input" this.changeSomethingPlusTwenty}}/>
  {{#if @first}}
    <MyChildComponent @something={{this.somethingPlusTwenty}} />
  {{/if}}
</div>

templates.components.my-component\.hbs

<input type="number" value={{this.something}} {{on "input" this.changeSomething}}/>
<MyChildComponent @first={{true}} @something={{this.something}}/>

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": {
  	"@ember/render-modifiers": "1.0.2",
    "@glimmer/component": "1.0.0"
  }
}