State in Controller

controllers.application\.js

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

class Stuff {
  constructor(label) {
		this.label = label;
  }

  @tracked toggled = false;
}

export default class ApplicationController extends Controller {
  // State lives here only
  data = [
    new Stuff('one'),
    new Stuff('two')
  ];

	// Actions to manage state
  @action
  toggleAll() {
    this.data[0].toggled = !this.data[0].toggled;
    this.data[1].toggled = !this.data[1].toggled;
  }

	@action
	toggle(item) {
    if (item.label === 'one') {
      console.log('Toggle one');
      this.data[0].toggled = !this.data[0].toggled;
    } else {
      console.log('Toggle two');
      this.data[1].toggled = !this.data[1].toggled;
    }
  }
}

templates.application\.hbs

<h1>Stuff</h1>

{{#each this.data as |item|}}
  <MyItem @item={{item}} @toggle={{this.toggle}} />
{{/each}}

<br>
<button {{on "click" this.toggleAll}}>Toggle All</button>

templates.components.my-item\.hbs

{{!-- Component has no logic, only gets stuff passed in! --}}
<button {{on "click" (fn @toggle @item)}}>Toggle</button> 
{{@item.label}} {{if @item.toggled "🔳" "⬜"}}<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": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}