https://github.com/bazzel/ember-workshop, tag 9.0.0

star-rating.hbs

{{#each starred}}
  <span class="glyphicon glyphicon-star"></span>
{{/each}}
{{#each unstarred}}
  <span class="glyphicon glyphicon-star-empty"></span>
{{/each}}

star-rating.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'span',
  starred: function() {
    return new Array(this.get('starCount'));
  }.property('starCount'),
  unstarred: function() {
    return new Array(5-this.get('starCount'));
  }.property('starCount')
});