New Twiddle

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';
import { inject as service } from '@ember/service';
import { schedule } from '@ember/runloop';

// For learning purposes only! Please do not do this
let log = document.createElement('div');
log.id = 'log';

document.body.appendChild(log);
let i = 1;

function appendEntry(str) {
    let p = document.createElement('p');
  	p.style.fontFamily = 'monospace';
  	p.innerText = `${i++}: ${str}`;
  	log.prepend(p);
}

const Router = EmberRouter.extend({
  location: 'none',
  routerState: service('router-state'),
  rootURL: config.rootURL,
  init() {
    this._super(...arguments);
    this.isInitialVisit = true;
    
  },
  willTransition() {
    if (this.isInitialVisit) {
      appendEntry('Initial visit');
    } else {
      appendEntry('Subsequent visit');
    }
  },
    
  didTransition() {
    appendEntry(`Transitioned`)
    
    this.get('routerState').set('isInitialVisit', false);
  }, 
});

Router.map(function() {
  this.route('a');
  this.route('b');
});


export default Router;

routes.a.js

import Ember from 'ember';

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

routes.application.js

import Ember from 'ember';

export default Ember.Route.extend({
    routerState: Ember.inject.service('router-state'),
    actions: {
    goBack() {
      // I need to do some check here to prevent user leaving our app, but isInitialVisit is always false
      console.error(this.get('routerState').isInitialVisit);
      if (!this.get('routerState').isInitialVisit) {
          	window.history.back();
      }
    },
  },
});

routes.b.js

import Ember from 'ember';

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

services.router-state.js

import Ember from 'ember';

export default Ember.Service.extend({
	isInitialVisit: true
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

#log {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: #efefe;
  border: 2px solid #999;
  height: 300px;
  overflow: scroll; 
}

templates.a.hbs

A Route

templates.application.hbs

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

<button {{action "goBack"}}>back</button>
{{link-to 'Page A' 'a'}}
{{link-to 'Page B' 'b'}}

<br>
<br>

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"
  }
}