Simple computed

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  baz: '1234',
  
  foo: Ember.computed('bar', 'baz', function () {
    return this.get('bar') + this.get('baz');
	})
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

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

{{my-component bar='test'}}

{{my-component foo='foo' bar='test'}}

templates.components.my-component.hbs

{{foo}}

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"
  }
}