computed.sort length

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  rowsSorting: ['name:desc'],
  rows: [{name: 'a'}, {name: 'b'}, {name: 'c'}, {name: 'd'}],
  sortedRows: Ember.computed.sort('rows', 'rowsSorting'),
  actions: {
    addRow() {
      let rows = this.get('rows')
      rows.push({name: Date.now()})
      this.set('rows', rows) // not works
      // rows.pushObject({name: Date.now()}) // works
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#each sortedRows key='name' as |row|}}
  {{row.name}}<br>
{{/each}}
<a href {{action 'addRow'}}>Add row</a>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}