New Twiddle

controllers.application.js

import Ember from 'ember';

const COUNTRIES = [
  { name: 'Iceland', code: 'IS' },
  { name: 'Germany', code: 'DE' },
  { name: 'Greece', code: 'GR' },
  { name: 'Spain', code: 'ES' }
];

export default Ember.Controller.extend({
  init() {
    this._super(...arguments);
    this.countries = [...COUNTRIES];
  },

  selectCountry({ target: { value: countryCode } }) {
    let country = this.countries.find(({ code }) => countryCode === code);
    this.set('selectedCountry', country);
  }
});

helpers.not-eq.js

import Ember from 'ember';

export function eq([a, b]) {
  return a !== b;
}

export default Ember.Helper.helper(eq);

templates.application.hbs

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

<h3>Selected country:</h3>
<p>
  {{#if this.selectedCountry}}
    {{this.selectedCountry.name}} {{this.selectedCountry.code}}
  {{else}}
    None selected 
  {{/if}}
</p>

<select onChange={{action this.selectCountry}}>
	{{#each this.countries as |country|}} 
    <option value={{country.code}}> 
      {{#if (not-eq this.selectedCountry.code country.code)}}
        {{country.name}} - 
      {{/if}}
      
      {{country.code}}
    </option>
  {{/each}}
</select>

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"
  }
}