sample.es6

import Ember from 'ember';

var { computed, getWithDefault } = Ember;

export default function(dependentKey) {
  return (
    computed(`${dependentKey}.@each`, function() {
      var emptyArray = Ember.A([]);
      var items      = getWithDefault(this, dependentKey, emptyArray);
      var length     = items.get('length');
      var randomItem = items[Math.floor(Math.random() * length)];

      return randomItem || '';
    })
  ).volatile();
};