class helper test

controllers.application\.js

import Controller from "@ember/controller";
import MyHelper from "../helpers/my-helper";

export default class AppController extends Controller {
    myHelper = MyHelper;
}

helpers.my-helper\.js

import Helper from '@ember/component/helper';

export default class MyHelper extends Helper {
  compute() {
    return "Hello World";
  }
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
{{my-helper 0}}
{{this.myHelper 1}}
{{#let (helper this.myHelper) as |h|}}
  {{h 2}}
{{/let}}

<br>

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": "3.28.0-beta.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}