New Twiddle

controllers.application.js

import Ember from 'ember';

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

helpers.is-active.js

// copy-pasted from the RFC example
// https://github.com/emberjs/rfcs/blob/master/text/0095-router-service.md#new-method-checking-for-active-route

import Helper from '@ember/component/helper';
import { inject as service } from '@ember/service';
import { observer } from '@ember/object';

export default Helper.extend({
  router: service(),
  compute([routeName]) {
    // this works
    //return this.get('router').isActive(routeName);

    // this does not work
    // and prevents the more complicated version from the rfc example working when a parameterless route is queried, because the empty context object gets passed in and triggers the bug
    // it only seems to happen on nested routes
    return this.get('router').isActive(routeName, [], {});
  },
  didTransition: observer('router.currentRoute', function() {
    this.recompute();
  })
});

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('dashboard', {path: '/'}, function() {});
  //this.route('wrapper', {path: '/wrapper'}, function() {
    //this.route('inner', {path: '/inner'});
  //});
});

export default Router;

templates.application.hbs

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

<li class="{{if (is-active 'dashboard') 'now-active'}}">
{{#link-to 'dashboard'}}Dashboard{{/link-to}}
</li>

{{!--
<li class="{{if (is-active 'wrapper') 'now-active'}}">
{{#link-to 'wrapper'}}Wrapper{{/link-to}}
</li>

<li class="{{if (is-active 'wrapper.inner') 'now-active'}}">
{{#link-to 'wrapper.inner'}}Wrapper-Inner{{/link-to}}
</li>
--}}

templates.dashboard.hbs

<h1>Dashboard</h1>

templates.wrapper.hbs

<h1>Wrapper</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.wrapper.inner.hbs

<h2>Inner</h2>

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"
  }
}