New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  queryParams: ['b'],
	a: "test",
  b: Ember.computed('a', {
    get() {
      return this.get('a');
    },
    set(key, value) {
      return value;
    }
  })
});

application.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  model: function() {
    return new Promise(function(resolve, reject) {
      resolve(['a','b','c']);
    });
  }
});

application.template.hbs

a: {{input value=a}}
b: {{input value=b}}

home.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  testComputed: Ember.computed('model', function() {
    console.log("Computed property evaluates");
    return this.get('model').slice(0,2);
  }),
  testObserver: Ember.observer('testComputed', function() {
    console.log("Observer fires");
    this.set('downstreamVal', this.get('testComputed')[0]);
  }),
  downstreamComputed: Ember.computed('testComputed', function() {
    console.log("Downstream computed fires");
  return this.get('testComputed')[1];
})
});

home.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  model: function() {
    return new Promise(function(resolve, reject) {
      resolve(['a','b','c']);
    });
  }
});

home.template.hbs

{{#each model as |item|}}
 {{item}}
{{/each}}
{{testComputed}}
{{downstreamVal}}

router.js

import Ember from 'ember';
import config from './config/environment';

var Router = Ember.Router.extend({
  location: config.locationType
});

Router.map(function() {
  this.route('home');
});

export default Router;

twiddle.json

{
  "version": "0.4.13",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.1.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember-template-compiler.js"
  }
}