Reverse sort order with Backbone.js

Question

With Backbone.js I\'ve got a collection set up with a comparator function. It\'s nicely sorting the models, but I\'d like to reverse the order.

How can I sort the m

Answer 1

The following worked well for me:

comparator: function(a, b) {
  // Optional call if you want case insensitive
  name1 = a.get('name').toLowerCase();
  name2 = b.get('name').toLowerCase();

  if name1 < name2
    ret = -1;
  else if name1 > name2
    ret = 1;
  else
    ret = 0;

  if this.sort_dir === "desc"
    ret = -ret
  return ret;
}

collection.sort_dir = "asc";
collection.sort(); // returns collection in ascending order
collection.sort_dir = "desc";
collection.sort(); // returns collection in descending order

Answer 2

For reverse order on id:

comparator: function(object) { return (this.length - object.id) + 1; }

Answer 3

Backbone.js's collection comparator relies on the Underscore.js method _.sortBy. The way sortBy is implemented ends up "wrapping" up javascript .sort() in a way that makes sorting strings in reverse difficult. Simple negation of the string ends up returning NaN and breaks the sort.

If you need to perform a reverse sort with Strings, such as reverse alphabetical sort, here's a really hackish way of doing it:

comparator: function (Model) {
  var str = Model.get("name");
  str = str.toLowerCase();
  str = str.split("");
  str = _.map(str, function(letter) { 
    return String.fromCharCode(-(letter.charCodeAt(0)));
  });
  return str;
}

It's by no means pretty, but it is a "string negator". If you don't have any qualms with modifying native object types in javascript, you could make you code clearer by extracting the string negator and adding it as a method on String.Prototype. However you probably only want to do this if you know what you are doing, because modifying native object types in javascript can have unforeseen consequences.