New Twiddle

components.lazy-image.js

import Ember from 'ember';

const { computed } = Ember;

export default Ember.Component.extend({
  loaded: computed({
    get() {
      return false; // default value
    },
    set(key, value) {
      if (value) {
        this.notifyLoaded();
      }
      return value;
    }
  }),
  notifyLoaded() {
    const onLoad = this.get('onLoad');
    if (onLoad) {
      onLoad();
    }
  },
  
  actions: {
    markLoaded() {
      this.set('loaded', true);
    },
    unload() {
      this.set('loaded', false);
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  actions: {
    imageLoaded() {
      alert('image was loaded!');
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{lazy-image notifyLoaded=(action 'imageLoaded')}}
<br>
<br>

templates.components.lazy-image.hbs

{{#if loaded}}
  <button {{action 'unload'}}>Unload</button>
{{else}}
  <button {{action 'markLoaded'}}>Mark loaded</button>
{{/if}}
<p>Loaded: {{loaded}}</p>

twiddle.json

{
  "version": "0.10.7",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.0",
    "ember-data": "2.10.0",
    "ember-template-compiler": "2.10.0",
    "ember-testing": "2.10.0"
  },
  "addons": {}
}