New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

helpers.dec.js

import Ember from 'ember';

export function dec([i]/*, hash*/) {
  console.log(i);
  return i - 1;
}

export default Ember.Helper.helper(dec);

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

<FooBar @i={{2}} />
<br>
<br>

templates.components.foo-bar.hbs

<p>{{@i}}</p>

{{#if @i}}
  <FooBar @i={{dec @i}} />
{{/if}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}