New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  items: Ember.computed(() => []),
  hasItems: Ember.computed.notEmpty('items'),
  
  actions: {
    add() {
      this.get('items').pushObject({});
    },
    
    clear() {
      this.get('items').clear();
    },
  },
});

templates.application.hbs

Has items: {{hasItems}}<br>
<button onclick={{action 'add'}}>Add</button>
<button onclick={{action 'clear'}}>Clear</button>

twiddle.json

{
  "version": "0.11.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.2",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.10.2",
    "ember-testing": "2.10.2"
  },
  "addons": {}
}