New Twiddle

application.controller.js

import Ember from 'ember';

var categories = [
  {
    id: 1,
    title: 'category 1'
  }, {
    id: 2,
    title: 'category 2'
  }, {
    id: 3,
    title: 'category 3'
  }];
export default Ember.Controller.extend({
  categories: categories,
  selectedCategories: Ember.K,
  actions: {
    selectedChanged(selected) {
      this.set('selectedCategories', selected);
    }
  }
});

application.template.hbs

<h1> List Group Disaster </h1>
<h2> select category </h2>
{{#list-group model=categories selectedChanged=(action "selectedChanged") as |lg m|}}
  {{lg.item text=m.title}}
{{/list-group}}
  
<h2> selected categories: </h2>
{{#list-group model=selectedCategories as |lg m|}}
  {{lg.item text=m.title}}
{{/list-group}}

list-group-item.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'li',
  classNames: ['list-group-item'],
  classNameBindings: ['isActive:active'],

  isActive: false,
  
  click() {
    this.toggleProperty('isActive');
    this.get('selectedChanged')(this.get('isActive'));
  }
});

list-group-item.template.hbs

{{#if hasBlock}}
  {{yield}}
{{else}}
  {{text}}
{{/if}}

list-group.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'ul',
  classNames: ['list-group'],
  selected: Ember.A(),
  actions: {
    itemSelected(model, isSelected) {
      let selected = this.get('selected');
      if (isSelected) {
        selected.addObject(model);
      } else {
        selected.removeObject(model);
      }
      //test if `this.get('selectedChanged')` exists
      //before invoking it
      this.get('selectedChanged')(selected);
    }
  }
});

list-group.template.hbs

  {{#each model as |m|}}
    {{yield (hash
      item=(component "list-group-item"
        selectedChanged=(action "itemSelected" m)
      )
    ) m}}
  {{/each}}

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.active {
  background-color: red;
}

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "beta",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "beta"
  }
}