computed property diffing

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  lastUpdate: null,
  
  didReceiveAttrs() {
    this._super(...arguments);
    
    this.set('lastUpdate', Date.now());
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  currentDate: null,
  
  isOld: Ember.computed('currentDate', () => false),
  
  init() {
  	this._super(...arguments);
    
    this.updateCurrentDate();
    setInterval(() => this.updateCurrentDate(), 1000);
  },
  
  updateCurrentDate() {
    this.set('currentDate', Date.now());
  }
});

templates.application.hbs

currentDate: {{currentDate}}<br>
isOld: {{isOld}}<hr>

{{my-component isOld=isOld}}

templates.components.my-component.hbs

lastUpdate: {{lastUpdate}}

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"
  }
}