New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  arr: [{},{},{},{},{},{},{},{},{},{}],
  
  arrayLength: Ember.computed.alias('arr.length'),
  
  arrayObserver: Ember.observer('arr.length', function() {
    alert(this.get('arr.length'));
  }),
  
  actions: {
    
    add() {
      let newItem = {};
      this.get('arr').splice(4, 0, newItem);
    },
    
    remove(item) {
      this.get('arr').removeObject(item);
    }
	
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>

{{#each arr as |item index|}}
	<p>item {{index}} <button {{action 'remove' item}}>x</button></p>

{{/each}}

Array length: {{arrayLength}} <button {{action 'add'}}>Add</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"
  }
}