wtf computed properties

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  sortAscending: true,
  notSortAscending: Ember.computed.not('sortAscending'),
  _items: Em.A([1, 2, 3]),
  
  items: Ember.computed('sortAscending', function() {
    if (this.get('sortAscending')) {
      return this.get('ascending');
    } else {
      return this.get('descending');
    }
  }),
  ascending: Ember.computed.sort('_items', function(a, b) {
    return a - b;
  }),
  descending: Ember.computed.sort('_items', function(a, b) {
    return b - a;
  }),
  
  actions: {
    addNumber() {
      this.get('_items').pushObject(4);
    }
  }
});

templates.application.hbs

<h1>Numbers</h1>

{{#each items as |item|}}
  {{item}}
{{/each}}

<h2>Sorting ascending: {{sortAscending}}</h2>
<button onclick={{action (mut sortAscending) notSortAscending}}>Change order</button>


<button {{action 'addNumber'}}>Add number</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"
  }
}