checkbox mut get

controllers.application.js

import Controller from '@ember/controller';

export default Controller.extend({
  appName: 'Ember Twiddle',
  controller_values: {'foo': 'bar'},
  controller_data: {},
  someval: '444'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{input type="checkbox" checked=checkedVal}} regular value - {{checkedVal}}
<br>
<br>

{{#x-select value=someval as |xs|}}
  {{#xs.option value="111"}} -- {{/xs.option}}
  {{#xs.option value="222"}} test it{{/xs.option}}
{{/x-select}}
<br>
{{someval}}
{{outlet}}
<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": "2.18.2",
    "ember-testing": "2.18.2"
  },
  "addons": {
    "ember-data": "2.18.5",
    "emberx-select": "3.1.1"
  }
}