New Twiddle

components.nav-for.js

import Ember from 'ember';

export default Ember.Component.extend({
  init() {
    this._super(...arguments);
  },
  didInsertElement() {
    this.set('header', document.getElementById(this.navId));
  }
});

controllers.application.js

import Ember from 'ember';

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

controllers.index.js

import Ember from 'ember';

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

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('a');
  this.route('b');
});

export default Router;

routes.a.js

import Ember from 'ember';

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

routes.b.js

import Ember from 'ember';

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

styles.app.css

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

.banner {
  width: 100%;
  padding: 30px;
  background: black;
  color: white;
}

.index-banner {
  color: white;
  background: blue;
}

.a-banner {
  color: white;
  background: red;
}

.b-banner {
  color: white;
  background: green;
}

templates.a.hbs

{{#nav-for navId="banner"}}
  <div class="a-banner banner">Page A with some stuff</div>
{{/nav-for}}

Page a

templates.application.hbs

<div id="banner"></div>

{{link-to 'a' 'a'}}
{{link-to 'b' 'b'}}
{{outlet}}

templates.b.hbs

{{#nav-for navId="banner"}}
<div class="b-banner banner">Page B With some different stuff</div>
{{/nav-for}}

page b

templates.components.nav-for.hbs

{{! note this is not a private api in newer versions }}
{{#-in-element this.header}}
  {{yield}}
{{/-in-element}}

templates.index.hbs

{{#nav-for navId="banner"}}
  <div class="index-banner banner">Index page</div>
{{/nav-for}}

Index

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"
  }
}