observing attrs.value

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  foo: 1,
  bar: 100,
  actions: {
    tap: function() {
			this.decrementProperty('foo');
    }
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{#test-component foo=foo bar=bar}}
  Hello from inside component.
{{/test-component}}

<input type="button" {{action 'tap'}} value="tap" />
<br>
<br>

test-component.component.js

import Ember from 'ember';

const { 
  observer, 
  Logger 
} = Ember;

export default Ember.Component.extend({
  obs1: 0,
  obs2: 0,
  barObs1: observer('bar', function() {
    Logger.log('bar observer fired!');
    this.incremementProperty('obs1');
  }),
  
  barObs2: observer('attrs.bar', function() {
    Logger.log('attrs.bar observer fired!');
    this.incrementProperty('obs2');
  }),
  
  didRender: function(attrs) {
		this._super();
    Logger.log(attrs);
    Logger.log(`foo: ${this.getAttr('foo')}`);
    Logger.log(`bar: ${this.getAttr('bar')}`);
  }
});

test-component.template.hbs

{{yield}}
<ul>
	<li>foo: {{foo}}</li>
  <li>bar: {{bar}}</li>
</ul>

<ul>
	<li>bar Observed: {{obs1}}</li>
  <li>attr.bar Observed: {{obs2}}</li>
</ul>

twiddle.json

{
  "version": "0.4.16",
  "EmberENV": {
    "FEATURES": {}
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "1.13.10",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.1.0/ember-data.js",
    "ember-template-compiler": "1.13.10"
  }
}