Tracked mutation example

controllers.application\.js

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

function getRandomInt() {
  return Math.floor(Math.random() * Math.floor(9999999));
}

export default class ApplicationController extends Controller {
  @tracked numbers = new Set();

  @action
  addRandomNumber() {
    this.numbers.add(getRandomInt());
    // Uncomment me to "fix" this
    // this.numbers = this.numbers;
  }
}

templates.application\.hbs

<button {{on "click" this.addRandomNumber}}>
  Add random number
</button>

<h1>Numbers</h1>

{{#each this.numbers as |number|}}
  <p>{{number}}</p>
{{/each}}

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"
  }
}