StackOverflow 60055682 but with tracked everything

components.demo\.hbs

<section>
  <h2>items in the component</h2>

  <ul>
    {{#each this.items as |item|}}
      <li>
        {{item.quantity}} x {{item.name}}
        <button class='button-sm' {{on 'click' (fn this.add item)}}>
          Add Item
        </button>

        <button class='button-sm' {{on 'click' (fn this.remove item)}}>
          Remove Item
        </button>
      </li>
    {{/each}}
  </ul>
</section>

<section>
  <h2>items in the service</h2>

  <ul>
    {{#each this.cart.items as |item|}}
      <li>
        {{item.quantity}} x {{item.name}}
      </li>
    {{/each}}
  </ul>
</section>

components.demo\.js

import Component from '@glimmer/component';
import { inject as service } from '@ember/service';
import { action, set } from '@ember/object';
import { tracked } from '@glimmer/tracking';
import { TrackedArray } from 'tracked-built-ins';

// Note that name and quantity are *not* tracked
class Item {
  @tracked name;
  @tracked quantity;
  
  constructor(id, name, quantity) {
    this.id = id;
    this.name = name;
    this.quantity = quantity;
  }
}

export default class DemoRoot extends Component {
  @service cart;

  @tracked items;

	constructor(owner, args) {
    super(owner, args);

    // Setup some default data for the demo
    this.items = [
      new Item(1, 'Apple', 1),
			new Item(2, 'Orange', 1),
      new Item(3, 'Carolina Reaper', 1),
    ];

    this.cart.items = [...this.items];
  }
 
  @action
  add(item) {
    for (let obj of this.items) {
      if (obj.id !== item.id) continue;
      
      obj.quantity = obj.quantity + 1;
    }
  }
  
  @action
  remove(item) {
    for (let obj of this.items) {
      if (obj.id !== item.id) continue;
      
      obj.quantity = obj.quantity - 1;
    }
  }
}

components.link\.hbs

<a ...attributes target="_blank">
  {{yield}}
</a>

components.title\.hbs

<h1>
	Answer to 
  
  <Link href="https://stackoverflow.com/questions/60055682/">
  	StackOverflow #60055682
  </Link>
</h1>

<em>Ember 3.16+</em>

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

helpers.as-formatted-string\.js

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

export default helper(function asFormattedString([a]/*, hash*/) {
  return a ? JSON.stringify(a, null, 2) : `${a}`;
});

helpers.eq\.js

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

export default helper(function eq([a, b]/*, hash*/) {
  return a === b;
});

services.cart\.js

import Service from '@ember/service';
import { tracked } from '@glimmer/tracking';
import { TrackedArray } from 'tracked-built-ins';

export default class CartService extends Service {
  @tracked items = new TrackedArray([]);
}

styles.app\.css

body {
  padding: 1rem;
}

li {
  margin: 0.5rem 0;
}

templates.application\.hbs

<link rel="stylesheet" href="https://cdn.shoelace.style/1.0.0-beta.25/shoelace.css">


<Title />

<br><br>

<Demo />

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",
    "ember-modifier": "1.0.3",
    "tracked-built-ins": "1.0.2"
  }
}