each/else

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  init() {
    this._super(...arguments);
    this.set('items', []); 
  },
  
  actions: {
    add(name) {
      this.get('items').pushObject(name);
    },
    clear() {
      this.set('items', []);
    }
  }
});

templates.application.hbs

There are {{items.length}} items:

<hr />

{{#each items as |item|}}
	[{{item}}]
{{else}}
  (no items)
{{/each}}

<hr />

<button onclick={{action 'add' 'red'}}>Red</button>
<button onclick={{action 'add' 'blue'}}>Blue</button>
<button onclick={{action 'add' 'green'}}>Green</button>

<hr />

<button onclick={{action 'clear'}}>Clear</button>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}