issue-16812

components.my-component.js

import Ember from 'ember';
import { later } from '@ember/runloop'

export default Ember.Component.extend({
  init() {
    this._super(...arguments);
    this.set('array', ['a', 'b', 'c']);
    this.addObserver('array.[]', () => console.log('changed'));
    later(() => this.array.replace(1, 1, ['9999']), 5000);
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{my-component}}
<br>
<br>

templates.components.my-component.hbs

{{#each array as |value index|}}
  {{index}}: {{value}}<br>
{{/each}}

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  }
}