Use jQuery to sort <li> elements that posses a data-index property

sort_li.js

// selecting the ul and children
var $categories = this.$el.find('ul.sortable'),
  $categoriesli = $categories.children('li');

// sorting the list
$categoriesli.sort(function(a,b){
  var an = $(a).find('div.sort-arrows').data('index'),
    bn = $(b).find('div.sort-arrows').data('index');

  if(an > bn) {
    return 1;
  }
  if(an < bn) {
    return -1;
  }
  return 0;
});
// re-attaching the ordered list
$categoriesli.detach().appendTo($categories);