basics

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('post', { path: '/post/:post_id' }, function() {
  	this.route('comments', function() {
    	this.route('new');
    })
  })
});

export default Router;

routes.post.comments.index.js

import Ember from 'ember';

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

routes.post.comments.js

import Ember from 'ember';

export default Ember.Route.extend({
  prefetch() {
    return new Ember.RSVP.Promise((resolve) => {
    	setTimeout(() => {
      	console.log('Route: comments');
        resolve();
      }, 1000);
    });
  },
  model(){}  
});

routes.post.comments.new.js

import Ember from 'ember';

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

routes.post.js

import Ember from 'ember';

export default Ember.Route.extend({
  prefetch() {
    return new Ember.RSVP.Promise((resolve) => {
    	setTimeout(() => {
      	console.log('Route: post');
        resolve();
      }, 3000);
    })
  },
  model(){}
});

templates.application.hbs

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

templates.post.comments.hbs

comments
<br>
{{outlet}}

templates.post.comments.index.hbs

index

templates.post.comments.new.hbs

new

templates.post.hbs

Post
<br>
{{outlet}}

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",
     "ember-prefetch": "3.1.4"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}