sample-dropdown

components.parent-component\.js

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

export default class DropdownComponent extends Component {
  @tracked feature = 'one';

  defaultOptions = ['one', 'two', 'three'];
  all = true;

  get options() {
    let list = this.defaultOptions;

    if (this.all)
      list.push('four', 'five');

    return list;
  }

  @action
  setFeature(event) {
    let feature = event.target.value;
    let list = this.options;

    // select another feature if the current isn't available
    if (list.indexOf(feature) == -1)
      feature = list[list.length - 1];

    this.feature = feature; // adjust as desired
  }
}

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>
<br>
<ParentComponent />

templates.components.dropdown-component\.hbs

Dropdown here:

<select {{on 'change' @onChange}}>
{{#each @options as |opt|}}
  <option>{{opt}}</option>
{{/each}}
</select>

templates.components.parent-component\.hbs

Parent component:<br>

selected feature: {{this.feature}}<br><br>

<DropdownComponent @options={{this.options}} @selectedFeature={{@model.feature}} @onChange={{this.setFeature}} />

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"
  }
}