backbone.projections is a set of projections for Backbone.Collection

• CappedCollection project underlying collection into a read-only collection of capped size

  {CappedCollection} = require 'backbone.projections'
  
  collection = new Collection [...]
  capped = new CappedCollection(collection, cap: 5)

  this way capped will contain no more than 5 models and will behave as a Backbone.Collection and will be in sync with underlying collection. CappedCollection supports comparator but if no comparator is provided then capped will have an order induced by underlying collection.

• FilteredCollection project underlying collection into a read-only collection of models which match some predicate

  {FilteredCollection} = require 'backbone.projections'
  
  collection = new Collection [...]
  filtered = new FilteredCollection collection,
    filter: (model) -> model.get('date').isToday()

  this way filtered will contain only models which have "today's date" and will behave as a Backbone.Collection and will be in sync with underlying collection. FilteredCollection supports comparator but if no comparator is provided then capped will have an order induced by underlying collection.