New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  init() {
    this._super(...arguments);
    
    this.set('_set', new Set());
    this.set('array', Ember.A());
  },
  
  actions: {
    add() {
      let element = new Date();
      
     	this._set.add(element);
      this.notifyPropertyChange('_set');
      this.array.pushObject(element);
    },
    remove(element) {
      this._set.remove(element);
      this.notifyPropertyChange('_set');
      
      this.array.removeObject(element);
    }
  }
});

templates.application.hbs

<button onclick={{action "add"}}>add</button><br>

<strong>Set</strong>
<ul>
  {{#each this._set as |el|}}
    <li>{{el}} <button onclick={{action "remove" el}}>x</button></li>
  {{/each}}
</ul>

<strong>Array</strong>
<ul>
  {{#each this.array as |el|}}
    <li>{{el}} <button onclick={{action "remove" el}}>x</button></li>
  {{/each}}
</ul>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}