New Twiddle

a.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  items: Ember.computed(function() {
  	return [
      {
      	title: 'item 1',
      },
      {
      	title: 'item 2',
      },
      {
      	title: 'item 3',
      },      
    ];
  }),
  
  actions: {
    toggleActiveItem(item) {
      this.set('activeItem', this.get('activeItem') !== item ? item : null);
    },
    
  },
});

a.route.js

import Ember from 'ember';

export default Ember.Route.extend({
});

a.template.hbs

{{#each items as |item|}}
  {{#accordion-item 
  	click=(action 'toggleActiveItem' item) 
    item=item
    activeItem=activeItem
    title=item.title
   }}
    <p>body</p>
  {{/accordion-item}}
{{/each}}

accordion-item.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  // isExpanded: Ember.computed.equal('item', 'activeItem'),
  item: undefined,
  activeItem: undefined,

  isExpanded: Ember.computed('activeItem', 'item', function() {
    return this.get('activeItem') === this.get('item');
  }),
});

accordion-item.template.hbs

<h3>{{title}}</h3>

{{#if isExpanded}}
	{{yield}}
{{/if}}

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

application.route.js

import Ember from 'ember';

export default Ember.Route.extend({
});

application.template.hbs

{{link-to 'a' 'a'}}

{{outlet}}

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
	this.route('a');
});

export default Router;

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": true,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
  }
}