New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  mySize: 'm',
  
  imageUrl: Ember.computed('mySize', 'image', function() {
    let { image, mySize } = this.getProperties('image', 'mySize');
    return Ember.get(image, `size.${mySize}.url`);
  })
});

routes.application.js

import Ember from 'ember';
var imgArr = [
  {
    image1: {
      size: {
        l: {
          url: 'image1_l.jpg',
        },
        m: {
          url: 'image1_m.jpg',
        },
        s: {
          url: 'image1_s.jpg',
        }
      }
    }
  },
  {
    image2: {
      size: {
        l: {
        url: 'image2_l.jpg',
        },
        m: {
        url: 'image2_m.jpg',
        },
        s: {
        url: 'image2_s.jpg',
        }
      }
    },
  }
];
export default Ember.Route.extend({
  model(){
    return imgArr;
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<h2>My Image array:</h2>
{{#each model as |image|}}
	{{get image (concat 'size.' mySize '.url')}}
{{/each}}

<br>
<br>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}