New Twiddle

controllers.application.js

import Ember from 'ember';
import { computed, set } from '@ember/object';
import { A } from '@ember/array';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  init() {
    this.set('data', [{value: '123'}]);
  },
  arrayComputed: computed('data.[].{value}', function() {
    return this.get('data').length;
  }),
  viaLength: computed('data.length', function() {
    return this.get('data').length;
  }),
  eachComputed: computed('data.@each.{value}', function() {
    return this.get('data').length;
  }),
  hashComputed: computed('data.{0,1,2}', function() {
    return this.get('data').length;
  }),
  actions: {
    addItemViaSet() {
      this.get('data').set(1, {value: 'abc'});
    },
    changeValueAtIndex1() {
      set(this.get('data')[1],'value', 'DEF');
    },
    notifyPropertyChange() {
      this.notifyPropertyChange('data')
    },
    addItemViaPush() {
      this.get('data').pushObject({value: '442'});
    },
    reset() {
      this.set('data', A([{value: '123'}]));
    },
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{#each data as |d|}}
item: {{d.value}}
{{/each}}
<br>
{{outlet}}
<br>
arrayComputed: {{arrayComputed}}
<br>
viaLength: {{viaLength}}
<br>
eachComputed: {{eachComputed}}
<br>
hashComputed: {{hashComputed}}
<br>
<button {{action "addItemViaSet"}}>addItemViaSet</button>
<br>
<button {{action "changeValueAtIndex1"}}>changeValueAtIndex1</button>
<br>
<br>
<button {{action "notifyPropertyChange"}}>notifyPropertyChange</button>
<br><button {{action "addItemViaPush"}}>addItemViaPush</button>
<br><button {{action "reset"}}>reset</button>

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"
  }
}