Using Array in Ember Octane

controllers.application\.js

import Controller from '@ember/controller';

import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';
import { A } from '@ember/array';
import { set } from '@ember/object';

class Age {
	@tracked value;
	
	constructor(val) {
  	this.value = val;
  }
}

export default class ApplicationController extends Controller {
  
	usersListData = A([
    {
      firstName: 'Ankush',
      lastName: 'Dharkar',
      age: new Age(30)
    },
    {
      firstName: 'Sindbad',
      lastName: 'the Sailor',
      age: new Age(40)
    }
  ])

	@action
	addNewUser () {
  	this.usersListData.pushObject({
    	firstName: 'David',
      lastName: 'Kopp',
      age: new Age(45)
    });
  }

  @action
	changeFirstname () {
  	const obj = this.usersListData.objectAt(0);
  
		// [1.]
    obj.age.value = 22;

		// [2.]
		set(obj, 'firstName', 'Taksh');
    set(obj, 'lastName', 'Channa');

    /*
    In order to make sure the context updates properly, you must invalidate the property when updating it. 
    1. You can mark the property as `@tracked`, or 
    2. Use `@ember/object#set`: https://api.emberjs.com/ember/3.21/functions/@ember%2Fobject/set
    */
  
  }
}

templates.application\.hbs

{{#each this.usersListData as |userItem|}}
  {{log userItem.age}}
  <h2>{{userItem.firstName}} {{userItem.lastName}} = {{userItem.age.value}}</h2>
{{/each}}

<button type="button" {{on "click" this.addNewUser}} >Add New User</button>

<button type="button" {{on "click" this.changeFirstname}}>Change 1st user</button>

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"
  }
}