computed('val') vs computed('val.[]')

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  actions: {
    replace(){
      this.set('data', []);
    },    
    add(){
      this.get('data').pushObject('something');
    },
    remove(){
      this.get('data').removeObject('something');
    }    
  },
  
  computed1: Ember.computed('data', function(){
  	return `Computed 1: ${this.get('data.length')}`;
  }),
  
  computed2: Ember.computed('data.[]', function(){
  	return `Computed 2: ${this.get('data.length')}`;
  })  
  
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  myArray: ['foo', 'bar', 'foobar']
});

templates.application.hbs

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

{{my-component data=myArray}}
<br>
<br>

templates.components.my-component.hbs

<button {{action 'add'}}>Add</button>
<button {{action 'remove'}}>Remove</button>
<button {{action 'replace'}}>Replace</button>

<hr>

<p>{{computed1}}</p>
<p>{{computed2}}</p>

{{yield}}

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"
  }
}