is-present helper

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  collection: ['a', 'b', 'c'],
  element: 'a'
});

helpers.is-present.js

import Ember from 'ember';

export function isPresent(params/*, hash*/) {
  let [collection, element] = params;
  return collection.includes(element);
}

export default Ember.Helper.helper(isPresent);

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>
{{collection}}
<br>
<br>
{{input value=element}}
<br>
<br>
{{is-present collection element}}
<br>
<br>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}