New Twiddle

controllers.application.js

import Ember from 'ember';
import PromiseMonitor from '../promise-monitor';

let promise = new Promise(resolve => setTimeout(() => resolve('Done'), 2500));

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  promise: new PromiseMonitor(promise)
});

promise-monitor.js

import { set } from '@ember/object';

export default class PromiseMonitor {
  constructor(promise) {
    this.result = null;
    this.isPending = true;
    this.isFulfilled = false;
    this.isRejected = false;
    this._promise = promise;
    
    promise.then(
      result => this._didFulfill(result),
      error => this._didReject(error)
    );
  }
  
  _didFulfill(result) {
    set(this, 'isPending', false);
    set(this, 'isFulfilled', true);
    set(this, 'result', result);
  }
  
  _didReject(error) {
    set(this, 'isPending', false);
    set(this, 'isRejected', true);
    set(this, 'result', error);
  }
}

templates.application.hbs

{{#if promise.isPending}}
  Waiting...
{{else}}
  {{promise.result}}
{{/if}}

twiddle.json

{
  "version": "0.14.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "2.18.2",
    "ember-template-compiler": "2.18.2",
    "ember-testing": "2.18.2"
  },
  "addons": {
    "ember-data": "2.18.2"
  }
}