An alternative community de facto standard is an addon called ember-concurrency that makes a lot of the promise confusion go away.

It can be installed with the command ember install ember-concurrency.

Pros

• Intuitive reasoning of complex asynchronous code.
• Offers a complete API for managing tasks.
• Can be canceled.
• Can be used directly in a component without the need of a proxy object.
• Destructures promises inside the task function.
• Can use JavaScript try / catch / finally blocks to manage asynchronous assignment, exceptions, and cleanup.
• Tasks are automagically cancelled on willDestroy event, avoiding errors setting values on destroyed objects (e.g. after a timer)

Cons

• Not builtin – requires ember install ember-concurrency
• Uses generator functions that can confuse developers used to promise chains.

JavaScript

import Ember from 'ember';
import { task, timeout } from 'ember-concurrency';

const { Component, set } = Ember;

export default Component.extend({
  myTask: task(function * () {
    set(this, 'error', null);
    try {
      yield timeout(2000);
      return 'Foobar';
    } catch (err) {
      set(this, 'error', error);
    }
  }).keepLatest()
});

Template

{{#if myTask.isIdle}}
  <button onclick={{perform myTask}}>
    Start Task
  </button>
{{else}}
  Loading&hellip;
{{/if}} 

{{#if myTask.last.value}}
  Done. {{myTask.last.value}}
{{/if}}

{{#if error}}
  Something went wrong. {{error}}
{{/if}}

Ember comes with a built in helper that will provide computed properties for the status of an asynchronous task.

Pros

• Built in – no need for an addon.
• Can be managed in the life cycle of a component.
• Provides convenient state properties that can drive the template logic.

Cons

• Must be wrapped in an Ember.Object and cannot be applied to an Ember.Component directly.
• Creates a disconnect between the original promise chain and the destructing of the content value.
• Is not very intuitive and can be difficult to reason with.
• Cannot be cancelled.

JavaScript

import Ember from 'ember';

const {
  Component, PromiseProxyMixin, get, set, computed,
  isPresent, run, RSVP: { Promise }
} = Ember;

const MyPromiseProxy = Ember.Object.extend(PromiseProxyMixin);

export default Component({
  myProxy: computed('promise', {
    get() {
      const promise = get(this, 'promise');
      return isPresent(promise) ? MyPromiseProxy.create({promise}) : null;
    }
  }),

  actions: {
    performTask() {
      const fakeTask = new Promise((resolve) => {
        run.later(resolve, 'Foobar', 2000);
      });
      set(this, 'promise', fakeTask);
    }
  }
});

Template

{{#if myProxy.isPending}}
  Loading…
{{else}}
  <button onclick={{action "performTask"}}>
    Start Task
  </button>
{{/if}}

{{#if myProxy.isFulfilled}}
  Done. {{myProxy.content}}
{{/if}}

{{#if myProxy.isRejected}}
  Something went wrong. {{myProxy.reason}}
{{/if}}