New Twiddle

controllers.application.js

import Ember from 'ember';

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

controllers.parent.child.js

import Ember from 'ember';

export default Ember.Controller.extend({
  actions : {
    callParent() {
      this.send("invokeParent");
    }
  }
});

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("parent", function() {
    this.route("child");
  })
});

export default Router;

routes.parent.js

import Ember from 'ember';

export default Ember.Route.extend({
  actions : {
    invokeParent(){
      alert("hi");
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{link-to "go to parent" "parent"}}

{{outlet}}
<br>
<br>

templates.parent.child.hbs

<h2>Inside Child</h2>
<button {{action "callParent"}}>click</button>

templates.parent.hbs

<h2>Inside Parent</h2>
{{link-to "Go to Child" "parent.child" }}
{{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"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}