Backbone Collection Cache

collection_cache.coffee

define [], ()->

  CollectionCache = ->
    cache = {}

    # returns true if the cache has the given key already
    cacheHasKey = (key)->
      cache.hasOwnProperty key

    # generates a unique key from given arguments
    genKey = (args)->
      MD5(JSON.stringify(args))

    # creates an instance, caches it, and returns the instance
    # the trick here is how the instance is created with a dynamic set of arguments
    set = (klass, args, key)->
      F = (args)->
        return klass.apply(@, args)
      F.prototype = klass.prototype
      instance = new F(args)
      cache[key] = instance

    # returns a collection instance and caches it if needed
    get: ()->
      klass = Array::shift.call arguments
      key = genKey arguments
      if cacheHasKey(key)
        cache[key]
      else
        set klass, arguments, key

  CollectionCache