New Twiddle

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  foo = "foo";
}

helpers.to-upper\.js

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

export default helper(function toUpper(params/*, hash*/) {
  return params[0].toUpperCase();
});

templates.application\.hbs

<table>
  <tr>
    <td><code>this.foo</code></td>
    <td>{{this.foo}}</td>
  </tr>
  <tr>
    <td><code>&lt;Input /&gt;</code></td>
    <td><Input /></td>
  </tr>
  <tr>
    <td><code>&lt;Input @value=\{{this.foo}} /&gt;</code></td>
    <td><Input @value={{this.foo}} /></td>
  </tr>
  <tr>
    <td><code>&lt;Input @value="foo" /&gt;</code></td>
    <td><Input @value="foo" /></td>
  </tr>
  <tr>
    <td><code>&lt;Input @value=\{{to-upper this.foo}} /&gt;</code></td>
    <td><Input @value={{to-upper this.foo}} /></td>
  </tr>
  <tr>
    <td><code>&lt;Input @value=\{{to-upper "foo"}} /&gt;</code></td>
    <td><Input @value={{to-upper "foo"}} /></td>
  </tr>
</table>

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"
  }
}