willTransition order

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  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('parent', function() {
    this.route('child');
  });
});

export default Router;

routes.parent.child\.js

import Route from '@ember/routing/route';

export default class ChildRoute extends Route {
  model() {
  	console.log('model hook of child');  
  }
  
  willTransition() {
    console.log('willTransition hook of parent');
  }
}

routes.parent\.js

import Route from '@ember/routing/route';

export default class ParentRoute extends Route {
  model() {
  	console.log('model hook of parent');  
  }
  
  willTransition() {
    console.log('willTransition hook of parent');
  }
}

templates.application\.hbs

<LinkTo @route="parent.child">Go to child route</LinkTo>
<LinkTo @route="index">Go back to index route</LinkTo>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}