New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  log(msg) {
    Ember.$('.log').append(msg);
    Ember.$('.log').append(Ember.$("<br><br>"));
  },
  writeObject(arg) {
    let str = "";
    for (let key in arg) {
      console.log(key);
      str += `${key}: ${arg[key]}`;
    }
    this.log(str);
  },
  
  actions: {
    firstAction() {
      this.log(`${[...arguments].length} argument(s)`);
      [...arguments].forEach(argument => this.writeObject(argument));
    }
  }
});

styles.app.css

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

label {
  display: block;
  line-height: 14px;
  padding: 0.3rem;
  margin-bottom: 0.7em;
}

input {
 height: 32px;
 width: 100%;
}

.log {
  background: #eee;
  color: #333;
  padding: 2rem;
  margin-top: 3rem;
  position: relative;
}

.log:before {
  position: absolute;
  top: 10px;
  left: 10px;
  font-size: 12px;
  font-weight: bold;
  content: 'Results';
}

templates.application.hbs

<h1>Ember Action Koans PT. 1</h1>
<label>onchange=\{{action 'firstAction'}}</label>
<input 
  placeholder="make a change on this input"
  type="text" 
  onchange={{action 'firstAction'}} />

<div class="log"></div>

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": {}
}