Comparing fixedSort and Ember.computed.sort behavior

controllers.application.js

import Ember from 'ember';

export function fixedSort(arrayProp, ...sortProps) {
  console.log(arrayProp, sortProps);
  let parsedProps = sortProps.map((prop) => {
    let [name, dir] = prop.split(':');
    return [name, dir === 'desc' ? 1 : -1];
  });
  let observerString = `${arrayProp}.@each.{${parsedProps.map(prop => prop[0]).join(',')}}`;
  function sortFn() {
    let array = this.get(arrayProp) || [];
    let sorted = array.slice();
    let nProps = parsedProps.length;
    sorted.sort(function(a, b) {
      let i = 0;
      while (i < nProps && Ember.get(a, parsedProps[i][0]) === Ember.get(b, parsedProps[i][0])) {
        i++;
      }
      if (i >= nProps) {
        return 0;
      } else if (Ember.get(a, parsedProps[i][0]) < Ember.get(b, parsedProps[i][0])) {
        return parsedProps[i][1];
      } else {
        return -parsedProps[i][1];
      }
    });
    console.log(arrayProp, sortProps, sorted.mapBy('created'));
    return sorted;
  }
  return Ember.computed.apply(Ember, [observerString, sortFn]);
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  sort: ['created:asc'],
	items: [{created: undefined},{created: new Date(2017,1,15)},{created: new Date(2017,1,10)},{created: undefined},{created: new Date(2017,1,12)},{created: undefined}],
  sortedItems: Ember.computed.sort('items', 'sort'),
  fixedSortItems: fixedSort('items', 'created:asc')
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{#each sortedItems as |item|}}
<div>{{if item.created item.created 'undefined'}}</div>
{{/each}}
<br>
{{#each fixedSortItems as |item|}}
<div>{{if item.created item.created 'undefined'}}</div>
{{/each}}
<br>
{{outlet}}
<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"
  }
}