Find next model in a Backbone Collection

backbone-collection-cycle.coffee

# Methods for cycling through the models in a Backbone Collection
# Usage:
#
#     c = new MyCollection([...])
#     nextModel = c.modelAfter(myModel)
#     myModel == c.modelBefore(nextModel) 
#     # true
#
class MyCollection extends Backbone.Collection

  # ...

  # Find previous model in the collection
  # move to end if we're off the start of the array
  modelBefore: (model) ->
    index = @indexOf(model) - 1 
    index = @.length - 1 if index < 0
    @at(index)
  
  # Find next model in the collection  
  # start over if we're off the end of the array
  modelAfter: (model) ->
    index = @indexOf(model) + 1 
    index = 0 if index == @.length 
    @at(index)