Ember DDEU (Data Down Events Up)

components.mega-input\.js

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

export default class MegaInputComponent extends Component {
  @tracked value = 42;
}

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';
export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
	@tracked
	externalValue = '';
	@action
	handleChange({detail}) {
  	this.externalValue = detail[0];
  }
}

helpers.emit-event\.js

import { helper } from '@ember/component/helper';

export default helper(function emitEvent([name]/*, hash*/) {
  return (node, params) => {
  	let event = new CustomEvent(name, { detail: params });
    node.dispatchEvent(event);
  }
});

templates.application\.hbs

<MegaInput {{on "mega-change" this.handleChange}} />
<br>
Value From event: {{this.externalValue}}

templates.components.mega-input\.hbs

<div ...attributes {{did-update (emit-event "mega-change") this.value}}>
    <Input @value={{this.value}} />
</div>

twiddle\.json

{
  "version": "0.17.0",
  "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/3.3.1/jquery.js",
    "ember": "3.17.0",
    "ember-template-compiler": "3.17.0",
    "ember-testing": "3.17.0"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "@ember/render-modifiers": "1.0.2"
  }
}