New Twiddle

controllers.application.js

import Ember from 'ember';

const { computed } = Ember;

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  fullName: computed('firstName', 'lastName', {
    get() {
      let { firstName, lastName } = this.getProperties('firstName', 'lastName');
      
      return `${firstName || ''} ${lastName || ''}`;
    },
      
    set(_key, value) {
      let [firstName, lastName] = value.split(' ');
      
      this.setProperties({firstName, lastName});
      
      return value;
    }
  })
});

templates.application.hbs

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

Fullname: {{fullName}}

<form>
<input placeholder="First name" value={{firstName}} onchange={{action (mut firstName) value="target.value"}}/>
<input placeholder="Last name" value={{lastName}} onchange={{action (mut lastName) value="target.value"}}/>
</form>

<form>
{{input value=newFullName}}
<button {{action (mut fullName) newFullName}}>Change fullname</button>
</form>
<br>
<br>

twiddle.json

{
  "version": "0.11.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.11.0",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.11.0",
    "ember-testing": "2.11.0"
  },
  "addons": {}
}