async routing

controllers.application.js

import Ember from 'ember';

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

router.js

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

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

Router.map(function() {
  this.route('foo');
  this.route('bar');
});

export default Router;

routes.foo.js

import Ember from 'ember';

export default Ember.Route.extend({
  actions: {
    async willTransition(transition) {
      try {
        console.log('Starting HTTP fetch');
        await Ember.$.getJSON('https://api.twitter.com/oauth/authenticate');
        console.log('Everything went ok');
        return true; 
      } catch (error) {
        console.log('Oh no, you should not be on `bar`');
        transition.abort();
      }
    }
  }
});

templates.application.hbs

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

<ul>
<li>
{{#link-to 'foo'}}foo{{/link-to}}
</li>
<li>
{{#link-to 'bar'}}bar{{/link-to}}
</li>
</ul>

<br>
<br>
{{outlet}}
<br>
<br>

templates.bar.hbs

BAR

templates.foo.hbs

FOO

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}