Derived state

components.my-component.js

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

const { computed } = Ember;

export default Ember.Component.extend({
  
  requiredInputA: null,
  requiredInputB: null,
  hasRequiredInputA: computed.bool('requiredInputA'),
  hasRequiredInputB: computed.bool('requiredInputB.length'),
  hasValidInputs: computed.and('hasRequiredInputA', 'hasRequiredInputB'),
  
  taskInstance: computed('requiredInputB.[]', 'requiredInputA', function(){
    return this.get('task').perform();
  }),
  
  task: task(function * () {
    this.incrementProperty('counter');
    yield timeout(1000);
    return [this.get('requiredInputA'), ...this.get('requiredInputB')];
  }).keepLatest(),
  
  // for demo purposes
  counter: 0
  
  
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
 
  foo: null,
  bar: null,
  
  actions : {
    addInputs(){
      this.set('foo', 'abc');
      this.set('bar', [1, 2]);
    },
    addAnother() {
      this.get('bar').pushObject('z');
    }
  }
  
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{my-component requiredInputA=foo requiredInputB=bar}}
<br>
<button {{action 'addInputs'}}>
Add valid inputs
</button>

<button {{action 'addAnother'}}>
click me next
</button>

templates.components.my-component.hbs

{{#if (not hasValidInputs)}}
  User feedback, no valid inputs
{{else if taskInstance.isRunning}}
  Show loading {{counter}}
{{else if taskInstance.isError}}
  Shoot an error.
{{else if taskInstance.value}}
  {{#each taskInstance.value as |v|}}
    {{v}}
  {{/each}}
{{/if}}

{{!--
You could also make a higher order query/data component to be used in block mode
that give you derived state for your other components.
// .hbs
{{yield (hash
           loading=taskInstance.isRunning
           error=task.last.isError
           value=taskInstance.value
           hasValidInputs=hasValidInputs
        )
}}

// usage
{{#my-query-component as |q|}}
  {{#if q.loading}}
  {{else if q.error}}
  {{else if q.value}}
  {{/if}}
{{/my-query-component}}
--}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1",
    "ember-truth-helpers": "*",
    "ember-concurrency": "*"
  }
}