New Twiddle

controllers.application.js

import Ember from 'ember';
import ArrayProxy from '@ember/array/proxy';
import { computed } from' @ember/object;

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
	_tempArr: computed(function() {
    return [];
  }),
  resolutionHistory: computed(function() {
    setTimeout(() => {
    	this.get('_tempArr').addObject('Hello!');
    }, 1000)
    
  	return ArrayProxy.create({
	    content: this.get('_tempArr')
    });
  }),
  
  isPending: computed('resolutionHistory.[]', function() {
  	return this.get('resolutionHistory').length === 0;
  })
});

templates.application.hbs

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

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"
  }
}