Array tracking/computed

controllers.application\.js

import Controller from '@ember/controller';
import { tracked as glimmerTracked } from '@glimmer/tracking';
import { tracked as builtinsTracked } from 'tracked-built-ins';
import { action, computed } from '@ember/object';

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

  untrackedArray = [];
  @glimmerTracked plainTrackedArray = [];
  @builtinsTracked builtinsTrackedArray = builtinsTracked([]);
  count = 1;

  @computed('untrackedArray.length')
  get untrackedArrayLength() {
    return this.untrackedArray.length;
  }

	@computed('plainTrackedArray.length')
  get plainTrackedArrayLength() {
    return this.plainTrackedArray.length;
  }

	@computed('builtinsTrackedArray.length')
  get builtinsTrackedArrayLength() {
    return this.builtinsTrackedArray.length;
  }

  @action addWithPush() {
    let index = this.count++;
    this.untrackedArray.push({ index });
    this.plainTrackedArray.push({ index });
    this.builtinsTrackedArray.push({ index });
  }

  @action addWithPushObject() {
    let index = this.count++;
    this.untrackedArray.pushObject({ index });
    this.plainTrackedArray.pushObject({ index });
    this.builtinsTrackedArray.pushObject({ index });
  }
}

templates.application\.hbs

<div>
  <button type="button" {{on "click" this.addWithPush}}>
    .push
  </button>

  <button type="button" {{on "click" this.addWithPushObject}}>
    .pushObject
  </button>
</div>

<h3><code>arr = []</code> (no tracking)</h3>
length: {{this.untrackedArray.length}}
<br/>
computed length: {{this.untrackedArrayLength}}

<h3><code>@tracked arr = []</code> (@glimmer/tracking)</h3>
length: {{this.plainTrackedArray.length}}
<br/>
computed length: {{this.plainTrackedArray.length}}

<h3><code>@tracked arr = tracked([])</code> (tracked-built-ins)</h3>
length: {{this.builtinsTrackedArray.length}}
<br/>
computed length: {{this.builtinsTrackedArrayLength}}

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",
    "tracked-built-ins": "1.0.2"
  }
}