New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  
  init() {
    this._super(...arguments);
    let attrs = Ember.keys(this.get('myVal'));
    attrs.forEach((attr) => {
    	attr = "myVal." + attr;
    });
    let computed = function() {
      return JSON.stringify(this.get('myVal'));
    };
    Ember.defineProperty(this, 'myValStringified', computed.property.apply(computed, attrs));
  },
  
  myVal: Ember.Object.create({
  	cats: 8,
    dogs: ['bowser','fred','chico'],
    fish: {
    		puffers: false
    }
  }),
 
  stringLastUpdated: Ember.computed('myValStringified', function() {
			return new Date();
  }),
});

templates.application.hbs

<p>My value stringified: {{myValStringified}}</p>

<p>myVal last updated: {{stringLastUpdated}}</p>

{{input type="text" value=myVal.cats}}

{{#each myVal.dogs as |dog|}}
	<br>{{input type="text" value=dog}}
{{/each}}

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}