This is a simple filtered collection implemented using Backbone.Collection. The goal here is to create a collection which, given a filter function, will just contain elements of the original which pass the filter. Supports add/remove/reset events of the original to modify the filtered version.

The main reason I did not just extend backbone is because by extending it, you shove all behaviors into one model, making it a jack-of-all-trades and potentially conflicting with behaviors of other extentions, not to mention making normal operaitons potentially slower. So the intention is to compose a filter chain pattern using these guys.

var YourCollection = Backbone.Collection.extend({model: YourModel});
var YourFilteredCollection = Backbone.FilteredCollection.extend({model: YourModel});
var allItems = new YourCollection(...);
// note the null, backbone collections want the pre-populated model here
// we can't do that since this collection does not accept mutations, it
// only mutates as a proxy for the underlying collection
var filteredItems = new YourFilteredCollection(null, {collection: allItems});
var filteredItems.setFilter(function(item) { return item.get('included') == true;});

And now filteredItems contains only those items that pass the filter. You can still manipulate the original:

allItems.add(..., {at: 5}); // at is supported too...

However, if you invoke {silent: true} on the original model, then you must reset the filter by invoking:

filteredItems.setFilter(); // no args = just re-filter

Same goes for remove and reset.

To clear the filtering completely, pass the value false to setFilter.