Filter with observable helpers

controllers.application.js

import Ember from 'ember';
const { Controller, A: emberArray } = Ember;

export default Controller.extend({
  appName: 'Ember Twiddle',
  
  actions: {
    selectState(stateID) {
      this.set('matchedFilters', [stateID]);
      this.get('matchedFiltersStable').pushObject(stateID);
    }
  },
  
  init() {
    this._super(...arguments);
    this.matchedFilters = emberArray([]);
    this.matchedFiltersStable = emberArray([]);
    
    this.states = [{
      id: '1',
      name: 'Tennessee',
    }, {
      id: '2',
      name: 'Florida',
    }, {
      id: '3',
      name: 'Georgia',
    }];
  }
});

helpers.is-selected-smart.js

import Ember from 'ember';

const { set, get, Helper, observer } = Ember;

export default Helper.extend({
  compute([selected, array = []]) {
    set(this, 'selected', selected);
    set(this, 'array', array);
    return get(this, 'array').indexOf(get(this, 'selected')) >= 0;
  },
  
  arrayContentDidChange: observer('array.[]', function() {
    this.recompute();
  })
});

helpers.is-selected.js

import Ember from 'ember';

export function isSelected(params/*, hash*/) {
	let selected = params[0];
  let options = params[1];
  return options.indexOf(selected) >= 0;;
}

export default Ember.Helper.helper(isSelected);

templates.application.hbs

<h1>Handlebar helper not executing on input change</h1>
<br>
<br>
<h2> With dumb helper - w/o observing </h2>

<select onchange={{action "selectState" value="target.value"}}>
{{#each states as |s|}}
	<option value={{s.id}} disabled={{is-selected s.id matchedFilters}}>{{s.name}}</option>
{{/each}}
</select>

<h2> With smart helper - observe array changes</h2>
<select onchange={{action "selectState" value="target.value"}}>
{{#each states as |s|}}
	<option value={{s.id}} disabled={{is-selected-smart s.id matchedFiltersStable}}>
  	{{s.name}}
   </option>
{{/each}}
</select>

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"
  }
}