Helpers and Tracked Properties

controllers.application\.js

import Controller from '@ember/controller';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';
import { inject as service } from '@ember/service';

export default class ApplicationController extends Controller {
  @service myService;
  @tracked foo = 'hello';

  @action
  updateFoo() {
    this.foo = (this.foo == 'hello') ? 'hi' : 'hello';
  }

  @action
  updateBar() {
    this.myService.bar = (this.myService.bar == 'world') ? 'earth' : 'world';
  }
}

helpers.my-helper\.js

import Helper from '@ember/component/helper';
import { inject as service } from '@ember/service';

export default class MyHelper extends Helper {
  @service myService;
  
  compute([foo]) {
    return `${foo} ${this.myService.bar}`;
  }
}

services.my-service\.js

import Service from '@ember/service';
import { tracked } from '@glimmer/tracking';

export default class MyService extends Service {
  @tracked bar = 'world';
}

templates.application\.hbs

<p>{{my-helper this.foo}}</p>
<p>
  <button {{on "click" this.updateFoo}}>Update Foo</button>
  <button {{on "click" this.updateBar}}>Update Bar</button>
</p>

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"
  }
}