Update counter

components.update-counter.js

import Component from '@ember/component'

export default Component.extend({
  
  // Note: I do believe that counter should start couting from 0
  // that has been fixed with following implementation.
  // Previous implemention updated counter on component initialization, so in fact it resulted with counting from 1

  count: 0,
  interval: 1000, // I would extract that property to be able to modify it quickly without jumping into details of implementation.
  
  init() {
    this._super(...arguments); // this line was missing
    // By extending init(), it's important that preserve that key functionality that init() does before you write whatever you need to write. Otherwise you will see an error in console.
    // NOTE: Altrernatively we could use didInsertElement() hook.
    this.start();     
  },
  
  // Destroy hook which prevents:
  // "Error: Assertion Failed: calling set on destroyed object
  willDestroy() {
    this._super(...arguments);
    this.stop();
  },
  
  start() {
    this.set('intervalId', window.setInterval(() => this.update(), this.get('interval')))
    // I used window.setInterval function to to be able to clear interval
  },
  
  update() {
    // that's simply our tick logic
    // we could simply modify this logic to use time if we need
    Ember.run(() => this.incrementProperty('count'))
  },
 	
  stop() {
    window.clearInterval(this.get('intervalId'));
    // After destroying element from the DOM, we won't call update anymore.
    // That's very important to prevent errors in console.
    // Initialy Ember.run.later attempted to set a value on non existing DOM object.
  },
  
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('blog', { path: '/blog' });
});

export default Router;

routes.blog.js

import Ember from 'ember';

export default Ember.Route.extend({
});

templates.application.hbs

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

{{outlet}}

{{#link-to "blog" }} "Blog" {{/link-to}}

<br>
<br>

templates.blog.hbs

Blog here

{{update-counter}}

{{#link-to "index" }} "Home" {{/link-to}}

templates.components.update-counter.hbs

{{count}}

tests.helpers.destroy-app.js

import { run } from '@ember/runloop';

export default function destroyApp(application) {
  run(application, 'destroy');
}

tests.helpers.resolver.js

import Resolver from '../../resolver';
import config from '../../config/environment';

const resolver = Resolver.create();

resolver.namespace = {
  modulePrefix: config.modulePrefix,
  podModulePrefix: config.podModulePrefix
};

export default resolver;

tests.helpers.start-app.js

import Ember from 'ember';
import Application from '../../app';
import config from '../../config/environment';

const { run } = Ember;
const assign = Ember.assign || Ember.merge;

export default function startApp(attrs) {
  let application;

  let attributes = assign({rootElement: "#test-root"}, config.APP);
  attributes = assign(attributes, attrs); // use defaults, but you can override;

  run(() => {
    application = Application.create(attributes);
    application.setupForTesting();
    application.injectTestHelpers();
  });

  return application;
}

tests.test-helper.js

import resolver from './helpers/resolver';
import {
  setResolver
} from 'ember-qunit';
import { start } from 'ember-cli-qunit';

setResolver(resolver);
start();

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}