get and set

controllers.application\.js

import Controller from '@ember/controller';
import { get, set } from '@ember/object';

export default class ApplicationController extends Controller {
  root = 'root state';

  get derived() {
    return `derived state derived from ${get(this, 'root')}`;
  }

  update = ({ target: { value } }) => {
    set(this, 'root', value);
  }
}

templates.application\.hbs

<p>Current root state is {{this.root}}</p>
<p>Current derived state is {{this.derived}}</p>
<label>
  type to change root state:
  <input {{on "input" this.update}} value={{this.root}} />
</label>

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"
  }
}