helper to determine active class

components.paginator-component.js

import Ember from 'ember';

export default Ember.Component.extend({
curr_page_idx: 0,
actions: {
  get_page_idx_clicked(idx) {
    this.set('curr_page_idx', idx);
  },
}
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items:[0, 1, 2, 3, 4]
});

helpers.active-class.js

import Ember from 'ember';

// active-class.js
export function activeClass(params/*, hash*/) {
  // PROBLEM: the value of active is always 0 even after the value 
  //  in the parent component has been successfully changed !!
  const [index, active] = params;
  return (index === active) ? 'active-class': '';
}

export default Ember.Helper.helper(activeClass);

styles.app.css

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{paginator-component total_pages_iterable=items}}
<br>
<br>

templates.components.paginator-component.hbs

<br> 
<br>
{{#each total_pages_iterable as |iter|}}
  <li>
    <a class="{{active-class iter curr_page_idx}}"
        {{action "get_page_idx_clicked" iter}} 
        href="javascript:void(0)">
      {{iter}}
    </a>
  </li>
{{/each}}

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}