kata

components.accordion-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  item: null,
  openItem: null,

  isOpen: Ember.computed('item', 'openItem', function() {
    return this.get('item') === this.get('openItem');
  }),
  classNames: ['item'],
  click() {
    this.get('clicked')(this.get('isOpen'));
  }
});

components.accordion-thing.js

import Ember from 'ember';

export default Ember.Component.extend({
  items: null, //passed-in
  openItem: null,
  actions: {
    toggleItem(item, itemWasOpen) {
      this.set('itemWasOpen', itemWasOpen);
      if (this.get('openItem') === item) {
        this.set('openItem', null);
      } else {
        this.set('openItem', item);
      }
    }
  }
});

controllers.application.js

import Ember from 'ember'
export default Ember.Controller.extend({
  listItems: [
    {title: "foo"},
    {title: "bar"}
  ]
});

styles.app.css

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

.item {
  padding: 10px 10px;
  cursor: pointer;
  border: 1px solid gray;
}
.item .open {
  background-color: green;
  height: 50px;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{accordion-thing items=listItems}}
{{outlet}}
<br>
<br>

templates.components.accordion-item.hbs

<div class={{if isOpen "open" "closed"}}>
  {{item.title}}
</div>

templates.components.accordion-thing.hbs

<div>{{itemWasOpen}}</div>
{{#each items as |item|}}
  {{accordion-item
    item=item
    openItem=openItem
    showStuff=(action showSomeStuff item)
    clicked=(action "toggleItem" item)}}
{{/each}}
{{yield}}

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": {}
}